The Nature of Gravity and How it can be Influenced

At the beginning of this book we discussed the so-called inertial forces and we distinguished several types of these forces: gravity, inertia and, as a special case of the latter, centrifugal force. At this point, we must concern ourselves in somewhat more detail with their nature.

It is the nature of these forces that they do not act only upon individual points of the surface of the object like other mechanical forces, but that they act simultaneously on all points even its internal ones. Since this special characteristic feature is common to all inertial forces, it is, therefore, entirely immaterial as far as a practical effect is concerned what type of inertial force is involved. It will always affect an object in the same fashion, as the force of gravity, and we will likewise feel it in every case as the well-known "weighty feeling," regardless of whether the force is gravity, inertia, centrifugal force or even the result of several of these forces. As a result of this complete uniformity of effect, it is possible that different types of inertial forces can mutually strengthen or weaken or also completely cancel each other.

We are already familiar with an example of the occurrence of a mutual strengthening of inertial forces when studying the ascent of space rockets. In this case, the force of gravity is increased due to the resulting inertia as long as there is thrust, something that makes itself felt for all practical purposes like a temporary increase of the force of gravity (Figure 22).

Figure 56. Carousel, accordance to Oberth. This equipment and that shown in Figure 57 are both designed to produce artificially the condition of an increased force of gravity for the purpose of carrying-out physiological experiments.

Key: 1. Counterbalancing weight; 2. Vehicle; 3. Pneumatic cushioning; 4. B Lateral arm; D. Tracks.

However, even under normal terrestrial conditions, the state of an increased force of gravity and even for any desired duration can be produced, when the centrifugal force is used for this purpose. Technical applications include, for example, different types of centrifuges. Their principle could be applied even on a large scale using a carrousel built especially for this purpose (Figure 56) or, better yet, in specially built giant centrifuges (Figures 57 and 58). At an appropriately high rate of rotation, a very significant multiplication of the gravitational effect would be achievable in this fashion.

Figure 57. Giant centrifuge according to the author's recommendation. This equipment and that shown in Figure 56 are both designed to produce artificially the condition of an increased force of gravity for the purpose of carrying out physiological experiments.

Key: 1. Beam with a slight clearance of motion; 2. Ball bearing; 3. Maintenance platform; 4. Tubular pole made from sheet iron or iron lattice tower; 5. Gondola for the experiments; 6. Drive motor; 7. Backup brake; 8. Braking occurs normally by the motor using energy recovery; 9. Concrete base; 10. Drive shaft.

Figure 58. The giant centrifuge in operation.

Key: 1. Gravity; 2. Centrifugal force.

On the other hand, a longer lasting decrease or cancellation of gravity (that is, generating a continuous weightless state) is not possible under terrestrial conditions, because to emphasize this once again the force of gravity cannot be eliminated in any other way whatsoever than through the opposition of another inertial force of the same magnitude. Therefore, an object can be prevented by supports from falling (i.e., responding to the force of gravity). Its weight, however, cannot be cancelled, a point proven by the continual presence of its pressure on the support. Any experiment to remove the influence of the force of gravity from an object, for instance, by some change of its material structure, would, no doubt, be condemned to failure for all times.

On the Earth's surface neither a correspondingly strong different force of gravity is available nor can centrifugal forces be generated in an object in such a way that it is transposed into an observable weightless state as a result of their effect.

Figure 59. The interplay of forces on a free falling object.

Key: 1. Inertia (activated by the acceleration due to gravity); 2. Free falling object; 3. Weight (as a result of the Earth's attraction); 4. Acceleration due to gravity of 9.81 m/sec2 (caused by the weight).

It is, however, possible on the Earth if only for a short duration to offset the force of gravity through the third inertial force, the force of inertia. Every day, we can experience this type of occurrence of weightlessness on ourselves or observe it on other objects, namely in the free fall state. That an object falls means nothing more than that it is moved towards the center of the Earth by its weight, and, more specifically, at an acceleration (of 9.81 m/sec2, a value familiar to us) that is exactly so large that the force of inertia activated in the object as a result exactly cancels the object's weight (Figure 59), because if a part of this weight still remained, then it would result in a corresponding increase of the acceleration and consequently of the inertia (opposing gravity in this case).

In the free fall or during a jump, we are weightless according to this reasoning. The sensation that we experience during the fall or jump is that of weightlessness; the behavior we observe in an object during free fall would be the same in a weightless state generated in another way. Since, however, falling can only last moments if it is not

supposed to lead to destruction (the longest times are experienced during parachute jumping, ski jumping, etc.), the occurrence of the weightless state on Earth is possible for only a very short time. Nevertheless, Oberth was successful in conducting very interesting experiments in this manner, from which conclusions can be made about the behavior of various objects and about the course of natural phenomena in the weight-free state.

Completely different, however, are the conditions during space travel. Not only can free fall last for days and weeks during space travel. It would also be possible to remove permanently the effect of gravity from an object: more specifically and as already stated in the introductory chapter by using the action of inertial forces produced by free orbital motion, in particular, of the centrifugal force. As has been previously stated, the space station makes use of this. An orbiting station is in the state of complete freedom from gravity lasting indefinitely ("a stable state of suspension"). 


 The Effect of Weightlessness on the Human Organism

How does the absence of gravity affect the human organism? The experience during free fall shows that a state of weightlessness lasting only a short time is not dangerous to one's health. Whether this would be true in the case of long-lasting weightlessness, however, cannot be predicted with certainty because this condition has not been experienced by anyone. Nevertheless, it may be assumed with a high probability, at least in a physiological sense, because all bodily functions occur through muscular or osmotic forces not requiring the help of gravity. Actually, all vital processes of the body have been shown to be completely independent of the orientation of the body and function just as well in a standing, a prone, or any other position of the body.

Only during very long periods in a weightless state could some injury be experienced, perhaps by the fact that important muscle groups would atrophy due to continual lack of use and, therefore, fail in their function when life is again operating under normal gravitational conditions (e.g, following the return to Earth). However, it is probable that these effects could be counteracted successfully by systematic muscular exercises; besides, it might be possible to make allowance for these conditions by means of appropriate technical precautions, as we will see later.

Apparently, the only organ affected by the absence of gravity is the organ of equilibrium in the inner ear. However, it will no longer required in the same sense as usual, because the concept of equilibrium after all ceases to exist in the weightless state. In every position of the body, we have then the same feeling: "up" and "down" lose their usual meaning (related to the environment); floor, ceiling and walls of a room are no longer different from one another.

However, in the beginning at least, the impression of this entirely unusual condition may cause a strongly negative psychological effect. Added to this is the effect that is directly exercised on the nervous system by the weightless state. The most important sensations related to this effect are as follows: the previously discussed effect on the organ of equilibrium, cessation of the perception of a supporting pressure against the body, and certain changes in the feelings in the muscles and joints.

However, this complex of feelings is known to us so far only from the free fall state because, as already discussed, we can experience freedom from gravity under terrestrial conditions only during falling; involuntarily, we will, therefore, feel anxiety related to the falling, as well as other psychological states aroused by this unusual situation during a cessation of the feeling of gravity, when the lack of gravity is not even caused by falling, but in another way (such as, in the space station by the effect of centrifugal force).

In any event, it can be expected based on previous experiences (pilots, ski jumpers, etc.) that it will be possible through adaptation to be able easily to tolerate the weightless state even in a psychological sense. Adapting occurs that much sooner, the more one is familiar with the fact that "weightless" and "falling" need not be related to one another. It can even be assumed that anxiety is altogether absent during a gradual release from the feeling of gravity.

Oberth has addressed all of these issues in depth. By evaluating his results, they can be summarized as follows: while weightlessness could certainly be tolerated over a long time, although perhaps not indefinitely, without significant harm in a physical sense, this cannot be stated with certainty in a psychological sense, but can be assumed as probable none the less. The course of the psychological impressions apparently would more or less be the following: in the beginning at least during a rapid, abrupt occurrence of the absence of gravity anxiety; the brain and senses are functioning extremely intensively, all thoughts are strongly factual and are quickly comprehended with a penetrating logic; time appears to move more slowly; and a unique insensitivity to pains and feelings of displeasure appear. Later, these phenomena subside, and only a certain feeling of elevated vitality and physical fitness remain, perhaps similar to that experienced after taking a stimulant; until finally after a longer period of adaptation, the psychological state possibly becomes entirely normal.


 The Physical Behavior of Objects when Gravity is Missing

In order to be able to form a concept of the general physical conditions existing in a weightless state, the following must be noted: the force of the Earth's gravity pulling all masses down to the ground and thus ordering them according to a certain regularity is no longer active. Accordingly almost following only the laws of inertia (inertial moment), bodies are moving continually in a straight line in their momentary direction of motion as long as no resistance impedes them, and they react solely to the forces (molecular, electrical, magnetic, mass-attracting and others) acting among and inside themselves. These unusual conditions must, however, lead to the result that all bodies show a completely altered behavior and that, in accordance with this behavior, our unique actions and inactions will develop in a manner entirely different from previous ones.

Therefore, human movement can now no longer occur by "walking." The legs have lost their usual function. In the absence of the pressure of weight, friction is missing under the soles; the latter stick, therefore, considerably less to the ground than even to the smoothest patch of ice. To move, we must either pull ourselves along an area with our hands (Figure 60, z), for which purpose the walls of the space station would have to be furnished with appropriate handles (for instance, straps similar to those of street cars) (Figures 60 and 61), or push ourselves off in the direction of the destination and float towards it (Figure 60, a).

It will probably be difficult for the novice to maintain an appropriate control over his bodily forces. This, however, is necessary: since he impacts the opposite wall of the room with the full force of pushing off, too much zeal in this case can lead very easily to painful bumps. For this reason, the walls and in particular all corners and edges would have to be very well cushioned in all rooms used by human beings (Figure 60).

Figure 60. A room of the space station in which a weightless state exists and which is furnished accordingly: The walls are completely cushioned and equipped with straps. No loose object is present.

K ....... Lockable small chests for holding tools and similar items.

L ....... Openings for admitting light (reference Page 143).

O ....... Openings for ventilation (reference Page 144).

z ....... Movement of people by pulling.

a ....... Movement of people by pushing off.

Key: 1. Direction of motion.

Pushing off can also be life threatening, more specifically, when it occurs not in an enclosed room but in the open; e.g., during a stay (in the space suit, see the following) outside of the space station, because if we neglected to take appropriate precautionary measures in this case and missed our destination while pushing off, then we would continually float further without end into the deadly vacuum of outer space. The no less terrible possibility of "floating off into space" now threatens as a counterpart to the terrestrial danger of "falling into the depths." The saying "man overboard" is also valid when gravity is missing, however in another sense.

Since bodies are now no longer pressed down upon their support by their weight, it, of course, has no purpose that an item is "hung up" or "laid down" at any place, unless it would stick to its support or would be held down by magnetic or other forces. An object can now only be stored by attaching it somewhere, or better yet locking it up. Therefore, the rooms of the space station would have to be furnished with reliably lockable small chests conveniently placed on the walls (Figures 60 and 61, K).

Clothes racks, shelves and similar items, even tables, as far as they are meant to hold objects, have become useless pieces of furniture. Even chairs, benches and beds can no longer satisfy their function; humans will have to be tied to them in order not to float away from them into any corner of the room during the smallest movement. Without gravity, there is neither a "standing" nor a "sitting" or "lying." In order to work, it is, therefore, necessary to be secured to the location of the activity: for example, to the table when writing or drawing (Figure 61). To sleep, we do not have to lie down first, however; we can take a rest in any bodily position or at any location in the room.

Figure 61. Writing in the weightless state: for this purpose, we have to be secured to the tabletop, for example, by means of leather straps (G) in order to remain at the table at all (without having to hold on). A man floats in from the next room through the (in this case, round) door opening, bringing something with him.

However, despite this irregularity in the physical behavior of freely moving objects caused by the absence of gravity, the manner is actually not completely arbitrary as to how these objects now come to rest. The general law of mass attraction is valid even for the space station itself and causes all masses to be attracted toward the common center of mass; however due to the relative insignificance of the entire mass they are attracted at such an extremely slight acceleration that traveling only one meter takes hours. However, nonsecured objects will finally impact one of the walls of the room either as a result of this or of their other random movement, and either immediately remain on this wall or, if their velocity was sufficiently large, bounce back again and again among the walls of the room depending on the degree of elasticity, floating back and forth until their energy of movement is gradually expended and they also come to rest on one of the walls. Therefore, all objects freely suspended within the space station will land on the walls over time; more specifically, they will approach as close as possible to the common center of mass of the structure.

This phenomenon can extend over hours, sometimes over many days, and even a weak air draft would suffice to interfere with it and/or to tear objects away from the wall, where they are already at rest but only adhering very weakly, and to mix them all up. Consequently, there is, practically-speaking, no regularity to the type of motion of weightless masses.

The latter is especially unpleasant when objects are in one room in significant numbers. If these objects are dust particles, they can be collected and removed in a relatively easy manner by filtering the air with vacuum cleaners or similar devices. However, if they are somewhat bigger as, for example, through the careless emptying of a sack of apples into a room, then the only alternative would be trapping them by means of nets. All objects must be kept in a safe place, because the ordering power of gravity now no longer exists: matter is "unleashed."

Also, clothing materials are on strike, because they no longer "fall," even if they were made of a heavy weave. Therefore, coats, skirts, aprons and similar articles of clothing are useless. During body movements, they would lay totally irregularly in all possible directions.

The behavior of liquids is especially unique in a weightless state. As is well known, they try under normal conditions to attain the lowest possible positions, consequently obeying gravity by always clinging completely to the respective supports (to the container, to the ground, etc.). If gravity is missing, however, the individual particles of mass can obey their molecular forces unimpeded and arrange themselves according to their characteristics.

In the weightless state therefore, liquids take on an independent shape, more specifically, the simplest geometric shape of an object: that of a ball. A prerequisite for this is, however, that they are subjected to only their forces of cohesion; that is, they are not touching any object they can "moisten." It now becomes understandable why water forms drops when falling. In this state, water is weightless, according to what has been previously stated; it takes on the shape of a ball that is distorted to the form of a drop by the resistance of air.

However, if the liquid is touching an object by moistening it, then overwhelmingly strong forces of cohesion and adhesion appear. The liquid will then strive to obey these forces, spreading out as much as possible over the surface of the object and coating it with a more or less thick layer. Accordingly for example, water in only a partially filled bottle will not occupy the bottom of the bottle, but, leaving the center empty, attempts to spread out over all the walls of the container (Figure 62). On the other hand, mercury, which is not a moistening liquid, coalesces to a ball and adheres to one wall of the container, remaining suspended in the bottle (Figure 63).

Figure 62. Dispersion of water in only a partially filled bottle in the absence of gravity.

Key: 1. Water; 2. An air-filled space surrounded on all sides by water.

Figure 63. Behavior of mercury in a bottle in the absence of gravity.

Key: 1. Ball of mercury.

In both instances, the position of the body is completely immaterial. Therefore, the bottle cannot be emptied by simply tilting it, as is usually the case. To achieve this effect, the bottle must either be pulled back rapidly (accelerated backwards, Figure 64) or pushed forward in the direction of the outlet and/or then suddenly halted in an existing forward motion (slowing it down in a forward movement, also as in Figure 64), or finally swung around in a circle (Figure 65).

Figure 64. Emptying a bottle in a weightless state by pulling it back.

Key: 1. Air bubbles entering.

Figure 65. In the absence of gravity, swinging a bottle of water in a circle in order to empty it. (In reality, the escaping liquid will probably not be dispersed in such a regular fashion as the discharge curve indicates.)

Key: 1. Motion of the bottle; 2. Direction of motion of the water; 3. The escaping water now freely suspended.

The liquid will then escape out of the bottle as a result of its power of inertia (manifested in the last case as centrifugal force), while taking in air at the same time (like gurgling when emptying the bottle in the usual fashion). A prerequisite for this, however, is that the neck of the bottle is sufficiently wide and/or the motion is performed with sufficient force that this entry of air can actually take place against the simultaneous outward flow of water.

[It is interesting to note that strictly speaking the described method of emptying a bottle in the absence of gravity by pulling it back or halting it proceeds in reality as if the water is poured out by turning the bottle upside down in the presence of gravity. Of course, these are completely analogous to physical phenomena {on Earth}, if the motion of pulling back and/or halting is performed exactly at the acceleration of gravity (9.81 m/sec2 for us), because as is known in accordance with the general theory of relativity, a system engaged in accelerated or decelerated motion is completely analogous to a gravitational field of the same acceleration. In the case of the described method of emptying, it can be stated that the forces of inertial mass that are activated by pulling back or stopping of the system operate in place of the missing gravity, including the bottle and its contents.]

After escaping from the bottle, the liquid coalesces into one or more balls and will continue floating in the room and may appear similar to soap bubbles moving through the air. Finally, every floating liquid ball of this type must then impact on one of the walls of the room. If it can moisten one of those walls, then it will try to spread out over them (left portion of Figure 66).

Figure 66. In the absence of gravity, escaping water would spread out over the walls in a room whose walls are easily moistened (e.g., they are somewhat damp; diagram on the left); in a room whose wall are not easily moistened (e.g., one coated with oil), the water coalesces into balls and adheres to the walls (diagram on the right).

Key: 1. Water; 2. Room with damp walls; 3. Room with walls coated with oil.

Otherwise as a result of the push, the liquid will scatter into numerous smaller balls, somewhat similar to an impacting drop of mercury. These balls float away along the walls or perhaps occasionally freely through the room, partially coalescing again or scattering once again until their kinetic energy has finally been expended and the entire amount of liquid comes to rest, coalesced into one or more balls adhering to the walls (right portion of Figure 66). (In this regard, compare the previous statements about the phenomena in a bottle, Figures 62 and 63.)

Given this unusual behavior of the liquid, none of the typical containers, such as bottles, drinking glasses, cooking pots, jugs, sinks, etc., could be used. It would hardly be possible to fill them. However, even if, by way of example, a bath could be prepared, we would not be able to take it because in the shortest time and to our disappointment, the water would have spread out of the bathtub over the walls of the room or adhered to them as balls.

Figure 67. In the absence of gravity, the otherwise usual liquid containers are replaced by sealable flexible tubes (left diagram), rubber balloons (center diagram) or syringe-type containers (right diagram).

Key: 1. Waterproof material (skin); 2. Rubber container; 3. Stopper functioning as a spigot here.

For storing liquids, only sealable flexible tubes, rubber balloons or containers with plunger-like, adjustable bottoms, similar to syringes, would be suitable (Figure 67), because only items of this nature can be filled (Figure 68) as well as easily emptied. Containers with plunger-like, adjustable bottoms function by pressing together the sides or by advancing the plunger to force out the contents (Figure 69). In the case of elastic balloons, which are filled by expanding them, their tension alone suffices to cause the liquid to flow out when the spigot is opened (Figure 70). These types of pressure-activated containers (fitted with an appropriate mouth piece) would now have to be used for drinking in place of the otherwise typical, but now unusable drinking vessels.

Figure 68. Filling a water vessel in the weightless state.

Key: 1. Wall; 2. Water supply; 3. Container; 4. The plunger is pushed forward for the purpose of removing water; 5. Connecting tube; 6. Tubular container being filled.

Similarly, the various eating utensils, such as dishes, bowls, spoons, etc., can no longer be used. If we made a careless move, we would have to float through the room chasing after their perhaps savory contents. Eating would, therefore, be possible only in two principal ways: either by eating the food in a solid form, such as bread, or drinking it in a liquid or mushy state using the pressure activated containers described above. The cook would have to deliver the food prepared in this manner.

Figure 69. In the absence of gravity, emptying a liquid container can be accomplished in an expedient manner only by pushing out (pressing out) the contents.

In his important activity, the cook would be faced with particularly significant problems, but they can also be overcome. The cook could use, for example, sealable electrical cooking appliances, constantly rotating when in use, so that (instead of the now missing gravity) the generated centrifugal force presses the contents against the walls of the container; there would also be other possibilities. In any case, cooking would not be easy, but certainly possible, as would eating and drinking. Washing and bathing as we know them would have to be completely dropped, however! Cleaning up could only be accomplished by rubbing with damp towels, sponges or the like lathered according to need, accepting whatever success this method would achieve.

Figure 70. In the case of elastic rubber balloons filled under pressure, the contents flow out of their own accord when the spigot is opened.

Key: 1. Expanded rubber container.

The more in depth we consider the situation, the more we must recognize that in reality it would in no way be an entirely unblemished pleasure to be able to float like angels, freed from all bothersome weight; not even if this state of weightlessness were perceived as pleasant. Because, gravity not only holds us in her grip; it also forces all other objects to the ground and inhibits them from moving chaotically, without regularity, freely left to chance. It is perhaps the most important force imposing order upon our existence. Where gravity is absent, everything is in the truest sense "standing on its head," having lost its foothold.


 Without Air

Human life can exist only in the presence of appropriately composed gaseous air: on the one hand, because life is a combustion phenomenon and, therefore, requires for its maintenance a permanent supply of oxygen, which the human organism, however, can only obtain from gaseous air by breathing; and, on the other hand, because the body must always be surrounded by a certain pressure, without which its water content would vaporize and the vessels would burst. It is necessary to provide a manmade supply of air if our terrestrial life is to be maintained in empty space.

To accomplish this, people in empty space must always be completely surrounded by absolutely airtight enclosures, because only within such capsules can the air be artificially maintained at the appropriate pressure and in the correct composition by automatic equipment.

Actually, we are only concerned with larger enclosed spaces extending from the size of a closet up to the size of an entire building, because only the latter would be possible for a longer stay. The walls of these structures would have to be built in accordance with the fundamentals of steam boiler construction because they have to withstand an internal air pressure (relative to empty space) of 1 atmosphere; they should not only have an appropriate strength but also curved surfaces if at all possible, because flat ones require special braces or supports in view of the over pressure. The nitrogen necessary for the air, and especially the oxygen, would always have to be maintained in sufficient supply in the liquid state in their own tanks through continual resupply from Earth.

However, in order to exist also outside of enclosed capsules of this type in empty space, airtight suits would have to be used, whose interior is also supplied automatically with air by attached devices. Such suits would be quite similar to the familiar underwater diving suits. We will call them "space suits." The subject of space suits will be addressed in more detail later.

It can be seen that we are dealing here with problems similar to those of remaining under water, that is, with submarine technology and diving practices. On the basis of the extensive experiences already gathered there on the question of supplying air artificially, it can be stated that this problem, without question, is entirely solvable also for a stay in empty space.


 Perpetual Silence Prevails in Empty Space

Air not only has direct value for life. Indirectly, it also has an important significance because to a far-reaching extent it influences natural phenomena that are extremely important for the functional activities of life: heat, light and sound.

Sound is a vibrational process of air and can, therefore, never exist in the absence of the latter. For this reason, a perpetual silence exists in empty space. The heaviest cannon could not be heard when fired, not even in its immediate vicinity. Normal voice communication would be impossible. Of course, this does not apply for the enclosed, pressurized rooms, within which the same atmospheric conditions will be maintained artificially as on the Earth's surface; it is true, however, outside of these rooms (in the space suit). There, voice communication would only be possible via telephones.


Sunshine during Nighttime Darkness

Even the lighting conditions are considerably altered in space. As is generally known, the concept of day is associated with the notion of a blue sky or sunlit clouds and scattering of light in all directions, without direct sunlight being necessary. All of these phenomena are, however, due only to the presence of the Earth's atmosphere, because in it a part of the incident radiation of the sun is refracted, reflected and scattered in all directions many times; one of the results of this process is the impression of a blue color in the sky. The atmosphere produces a widespread and pleasant, gradual transition between the harshness of sunlight and darkness.

This is all impossible in empty space because air is absent there. As a result, even the concept of day is no longer valid, strictly speaking. Without letup, the sky appears as the darkest black, from which the infinite number of stars shine with extreme brightness and with a constant untwinkling light, and from which the sun radiates, overwhelming everything with an unimaginably blinding force.

And yet as soon as we turn our gaze from it, we have the impression of night, even though our back is being flooded by sunlight because, while the side of the object (e.g., an umbrella) turned towards the sun is brightly illuminated by its rays, nighttime darkness exists on the back side. Not really complete darkness! After all, the stars shine from all sides and even the Earth or Moon, as a result of their reflectivity, light up the side of the object in the sun's shadow. But even in this case, we observe only the harshest, brightest light, never a mild, diffuse light.


Unlimited Visibility

In one regard however, the absence of air also has advantages for lighting conditions in empty space. After all, it is generally known what great effect the property of air exerts on visibility (e.g., in the mountains, at sea, etc.), because even on clear days, a portion of the light is always lost in the air, or rather through small dust and mist particles constantly suspended in it.

The latter effect is, however, very disadvantageous for all types of long range observations, especially those of astronomy. For this reason, observatories are built if at all possible at high altitudes on mountains because there the air is relatively the clearest. However, there are limits. Furthermore, the flickering of fixed stars, likewise a phenomenon caused only by the presence of air, cannot be avoided even at these high locations. Neither is it possible to eliminate the scattered light (the blue of the sky), which is very bothersome for astronomical observations during the day and is caused also by the atmosphere, thus making it very difficult to investigate those heavenly bodies that cannot be seen during complete darkness, such as Mercury, Venus, and, not least of all, the sun itself.

All of these adverse conditions are eliminated in the empty space of the universe; here, nothing weakens the luminosity of the stars; the fixed stars no longer flicker; and the blue of the sky no longer interferes with the observations. At any time, the same favorable, almost unlimited possibilities exist, because telescopes of any arbitrary size, even very large ones, could be used because optical obstructions no longer exist.


Without Heat

Especially significant is the effect the absence of air exerts on the thermal conditions of outer space. Because as we know today heat is nothing more than a given state of motion of the smallest material particles of which the materials of objects are composed, its occurrence is always associated with the supposition that materials exist in the first place. Where these materials are missing, heat cannot, therefore, exist: empty space is "heatless" for all practical purposes. Whether this is completely correct from a theoretical standpoint depends on the actual validity of the view expressed by some experts that outer space is filled with a real material, distributed very finely, however. If a total material emptiness exists, then the concept of temperature loses its meaning completely.

This view does not contradict the fact that outer space is permeated to a very high degree by the sun's thermal rays and those of the other fixed stars, because the thermal rays themselves are not equivalent with heat! They are nothing more than electromagnetic ether waves of the same type as, for example, light or radio waves; however, they have a special property in that they can generate, as soon as they impact some material, the molecular movement that we call heat. But this can only happen when the waves are absorbed (destroyed) by the affected materials during the impacting, because only in this case is their energy transmitted to the object and converted into the object's heat.

Thus, the temperature of a transparent object or of one polished as smooth as a mirror will only be slightly elevated even during intense thermal radiation. The object is almost insensitive to thermal radiation, because in the first case, the rays are for the most part passing through the object and, in the latter case, the rays are reflected by the object, without being weakened or destroyed; i.e., without having lost some part of their energy. If, on the other hand, the surface of the object is dark and rough, it can neither pass the incident rays through nor reflect them: in this case, they must be absorbed and hence cause the body to heat up.

This phenomenon is, however, not only valid for absorption but also for the release of heat through radiation: the brighter and smoother the surface of an object, the less is its ability to radiate and consequently the longer it retains its heat. On the other hand, with a dark, rough surface, an object can cool down very rapidly as a result of radiation.

The dullest black and least brightly reflecting surfaces show the strongest response to the various phenomena of thermal emission and absorption. This fact would make it possible to control the temperature of objects in empty space in a simple fashion and to a large degree.

Figure 71. Heating of an object in empty space by means of solar radiation by appropriately selecting its surface finish.

Key: 1. Object; 2. Solar radiation; 3. Highly reflecting surface (impeding cooling by emission); 4. Dull black (causing heating by absorption).

If the temperature of an object is to be raised in space, then, as discussed above, its side facing the sun will be made dull black and the shadow side brightly reflecting (Figure 71); or the shadow side is protected against outer space by means of a mirror (Figure 72). If a concave mirror is used for this purpose, which directs the solar rays in an appropriate concentration onto the object, then the object's temperature could be increased significantly (Figure 73).

Figure 72. Heating of a body by protecting its shadow side against empty space by means of a mirror.

Key: 1. Mirror; 2. Polished side; 3. Object; 4. Solar radiation

Figure 73. Intensive heating of an object by concentrating the rays of the sun on the object by means of a concave mirror.

Key: 1. Concave mirror; 2. Object; 3. Solar radiation.

Figure 74. Cooling an object down in empty space by appropriately selecting its surface finish.

Key: 1. Object; 2. Solar radiation; 3. Dull black (promoting cooling through emission); 4. Highly reflective surface (impeding heating by radiation).

If, on the other hand, an object is to be cooled down in outer space, then its side facing the sun must be made reflective and its shadow side dull black (Figure 74); or it must be protected against the sun by means of a mirror (Figure 75). The object will lose more and more of its heat into space as a result of radiation because the heat can no longer be constantly replaced by conduction from the environment, as happens on Earth as a result of contact with the surrounding air, while replenishing its heat through incident radiation would be decreased to a minimum as a result of the indicated screening. In this manner, it should be possible to cool down an object to nearly absolute zero (273 Celsius). This temperature could not be reached completely, however, because a certain amount of heat is radiated by fixed stars to the object on the shadow side; also, the mirrors could not completely protect against the sun.

Figure 75. Cooling an object by protecting it against solar radiation by means of a mirror.

Key: 1. Object; 2. Solar radiation; 3. Mirror; 4. Reflective side.

By using the described radiation phenomena, it would be possible on the space station not only to provide continually the normal heat necessary for life, but also to generate extremely high and low temperatures, and consequently also very significant temperature gradients.


Designing the Space Station

The physical conditions and potentials of empty space are now familiar to us. Here is an idea of how our space station would have to be designed and equipped: In order to simplify as far as possible the work to be performed in outer space when constructing this observatory (this work only being possible in space suits), the entire structure including its equipment would have to be assembled first on Earth and tested for reliability. Furthermore, it would have to be constructed in such a manner that it could easily be disassembled into its components and if at all possible into individual, completely furnished "cells" that could be transported into outer space by means of space ships and reassembled there without difficulty. As much as possible, only lightweight metals should be used as materials in order to lower the cost of carrying them into outer space.

The completed, ready-to-use structure would, in general, look as follows: primarily, it must be completely sealed and airtight against empty space, thus permitting internally normal atmospheric conditions to be maintained by artificial means. In order to reduce the danger of escaping air, which would happen if a leak occurred (e.g., as a result of an impacting meteor), the space station would be partitioned in an appropriate manner into compartments familiar from ship building.

Since all rooms are connected with one another and are filled with air, movement is easily possible throughout the inside of the space station. Space travelers can, however, only reach the outside into empty space by means of so-called air locks. This equipment, (used in caissons, diving bells, etc.) familiar from underwater construction, consists primarily of a small chamber that has two doors sealed airtight, one of which leads to the inside of the station and the other to the outside (Figure 76).

Figure 76. Basic layout of an air lock for moving from an air- filled room (e.g., the inside of the space station) to empty space. Drawing the air out of the lock during "outgoing" occurs mostly by pumping the air into the station for reasons of economy; only the residual air in the lock is exhausted into empty space. [Editor's Note: This second sentence was a footnote].

Key: 1. Air outlet valve; 2. Air intake valve; 3. Outside door; 4. Outer space (airless); 5. Air lock; 6. Inside door; 7. Inside of the station (air-filled, pressure of 1 at absolute); 8. To air pump.

If for example, a space traveler wants to leave the space station ("outgoing" or egress), then, dressed in the space suit, he enters the lock through the inside door, the outside door being locked. Now the inside door is locked and the air in the lock is pumped out and finally exhausted, thus allowing the traveler to open the outer door and float out into the open. In order to reach the inside of the space station ("incoming" or ingress), the reverse procedure would have to be followed.

For operations and the necessary facilities of the space station, it is important to remember that absolutely nothing is available locally other than the radiation of the stars, primarily those of the sun; its rays, however, are available almost all the time and in unlimited quantity. Other substances particularly necessary for life, such as air and water, must be continually supplied from the Earth. This fact immediately leads to the following principle for the operation of the space station: exercise extreme thrift with all consumables, making abundant use instead of the energy available locally in substantial quantities in the sun's radiation for operating technical systems of all types, in particular those making it possible to recycle the spent consumables.


The Solar Power Plant

The solar power plant for that purpose (Figure 77) represents, therefore, one of the most important systems of the space station. It delivers direct current, is equipped with a storage battery and is comparable in principle to a standard steam turbine power plant of the same type. There are differences, however: the steam generator is now heated by solar radiation, which is concentrated by a concave mirror in order to achieve sufficiently high temperatures (Figure 77, D); and cooling of the condenser occurs only by radiating into empty space, so it must be opened towards empty space and shielded from the sun (Figure 77, K).

Figure 77. Diagram of the solar power plant of the space station.

Key: 1. Steam turbine; 2. Shaft; 3. Storage battery; 4. Electrical generator; 5. Solar radiation; 6. Steam generator; 7. Concave mirror; 8. Pump; 9. Condenser; 10. Radiation out into empty space.

In accordance with our previous explanations, this causes both the steam generator and condenser to be painted dull black on the outside. In essence, both consist only of long, continuously curved metal pipes, so that the internal pipe walls, even in a weightless state, are always in sufficiently strong contact with the working fluid flowing through them (see Figure 77).

This working fluid is in a constant, loss-free circulation. Deviating from the usual practice, rather than water (steam), a highly volatile medium, nitrogen, is used in this case as a working fluid. Nitrogen allows the temperature of condensation to be maintained so low that the exceptional cooling potential of empty space can be used. Furthermore, an accidental escape of nitrogen into the rooms of the space station will not pollute its very valuable air.

Since it is only the size of the concave mirror that determines how much energy is being extracted from solar radiation, an appropriately efficient design of the power plant can easily ensure that sufficient amounts of electrical and also of mechanical energy are always available on the space station. Furthermore, since heat, even in great amounts, can be obtained directly from solar radiation, and since refrigeration, even down to the lowest temperatures, can be generated simply by radiating into empty space, the conditions exist to permit operation of all types of engineering systems.


Supplying Light

Lighting the space station can be accomplished very easily because this requires almost no mechanical equipment can be achieved directly from the sun, which after all shines incessantly, disregarding possible, yet in every case only short, passes by the space station through the Earth's shadow.

For this purpose, the walls have round openings similar to ship's bull's eyes (Figures 60 and 61, L) with strong, lens-type glass windows (Figure 78). A milkwhite coloring or frosting of the windows, and also an appropriate selection of the type of glass, ensure that sun light is freed of all damaging radiation components, filtered in the same way as through the atmosphere, and then enters into the space station in a diffuse state. Therefore, the station is illuminated by normal daylight. Several of the bull's eyes are equipped with special mirrors through which the sun's rays can be directed on the bull's eyes when needed (Figure 79). In addition, artificial (electrical) lighting is provided by extracting current from the solar power plant.

Figure 78. Lighting bull's eye.

Key: 1. Interior of the station; 2. Diffuse light; 3. Sealing material; 4. Bracing; 5. Solar radiation; 6. Empty space; 7. Glass lens.

Figure 79. The mirror reflects the rays of the sun directly on the window.

Key: 1. Mirror; 2. Solar radiation; 3. Window and interior of the space station.


Supplying Air and Heat

Even heating the space station takes place by directly using solar radiation, more specifically, according to the principle of heating air simultaneously with ventilation.

Figure 80. Schematic representation of a ventilation system. The cooled and heated pipes could be built, for example, similar to the ones shown in Figure 75, D and/or K.


Key: 1. Used air from the rooms of the space station; 2. Fan; 3. Dust filter; 4. Dust separation; 5. Cooled pipe; 6. Cooled by radiating into empty space; 7. Heated pipe; 8. Heated by solar radiation; 9. Mixer; 10. Water and carbon dioxide separation; 11. Heating the air to the required temperature; 12. Oxygen and water supply; 13. Regenerated and heated air to the rooms where it is consumed.

For this purpose, the entire air of the space station is continuously circulating among the rooms requiring it and through a ventilation system where it is cleaned, regenerated, and heated. A large, electrically driven ventilator maintains air movement. Pipelines necessary for this process are also available. They discharge through small screened openings (Figures 60 and 61, O) into the individual rooms where the air is consumed. The ventilation system (Figure 80) is equipped similarly to the air renewing device suggested by Oberth. At first, the air flows through a dust filter. Then it arrives in a pipe cooled by radiating into outer space; the temperature in this pipe is lowered gradually to below 78 Celsius, thus precipitating the gaseous admixtures; more specifically, first the water vapor and later the carbon dioxide. Then, the air flows through a pipe heated by the concentrated rays of the sun, thus bringing it to the temperature necessary to keep the rooms warm. Finally, its oxygen and moisture contents are also brought to the proper levels, whereupon it flows back into the rooms of the space station.

This process ensures that only the oxygen consumed by breathing must be replaced and consequently resupplied from the ground; the non-consumed components of the air (in particular, its entire nitrogen portion) remain continually in use. Since the external walls of the space station do not participate in this heating procedure, these walls must be inhibited as much as possible from dissipating heat into outer space through radiation; for this reason, the entire station is highly polished on the outside.


Water Supply

The available water supply must also be handled just as economically: all the used water is collected and again made reusable through purification. For this purpose, large distillation systems are used in which the evaporation and subsequent condensation of the water is accomplished in a similar fashion as was previously described for the solar power plant: in pipes heated by the concentrated rays of the sun (Figure 77, D) and cooled by radiating into outer space (Figure 77, K).


Long Distance Communications

The equipment for long distance communication is very important. Communication takes place either through heliograph signaling using a flashing mirror, electrical lamps, spot lights, colored disks, etc., or it is accomplished electrically by radio or by wires within the confined areas of the space station.

In communicating with the ground, use of heliograph signaling has the disadvantage of being unreliable because it depends on the receiving station on the Earth being cloudless. Therefore, the space station has at its disposal large radio equipment that makes possible both telegraph and telephone communications with the ground at any time. Overcoming a relatively significant distance as well as the shielding effect exerted by the atmosphere on radio waves (Heaviside layer),* are successful here (after selecting an appropriate direction of radiation) by using shorter, directed waves and sufficiently high transmission power, because conditions for this transmission are favorable since electric energy can be generated in almost any quantities by means of the solar power plant and because the construction of any type of antenna presents no serious problems as a result of the existing weightlessness.


Means of Controlling the Space Station

Finally, special attitude control motors ("momentum wheels") and thrusters are planned that serve both to turn the space station in any direction and to influence its state of motion as necessary. On the one hand, this option must exist to be able to maintain the space station in the desired orientation relative to the Earth as well as in the required position relative to the direction of the rays of the sun. For this purpose, not only must all those impulses of motion (originating from outside of the system!) that are inevitably imparted to the space station again and again in the traffic with space ships be continually compensated for, but the effect of the Earth's movement around the sun must also be continually taken into account.

On the other hand, this is also necessary in order to enable the space station to satisfy its special tasks, which will be discussed later, because any changes of its position in space must be possible for performing many of these tasks and finally because the necessity can occasionally arise for repositioning the station in relation to the Earth's surface.

The attitude control motors are standard direct current electrical motors with a maximum rate of revolution as high as possible and a relatively large rotor mass. Special brakes make it possible rapidly to lower or shut off their operation at will. They are installed in such a manner that their extended theoretical axes of rotation go through the center of mass of the station.

Figure 81. Operating characteristics of a thruster motor (see the text).

Key: 1. Station; 2. Stator of the motor; 3. Rotor (armature) of the motor; 4. Axis of rotation going through the center of mass of the station.

Now, if an attitude control motor of this type is started (Figure 81), then its stator (the normally stationary part of the electrical motor), and consequently the entire station firmly connected to the motor rotate simultaneously with its rotor (armature) around the axis of the motor however, in the opposite direction and, corresponding to the larger mass, much more slowly than the rotor. More specifically, the station rotates until the motor is again turned off; its rate of rotation varies depending on the rate of revolution imparted to the rotor of the motor. (In the present case, there is a "free system," in which only internal forces are active.) Since these motors are oriented in such a fashion that their axes are perpendicular to one another like those of a right angle, three dimensional coordinate system (Figure 82), the station can be rotated in any arbitrary direction due to their cooperative combined effects.

Figure 82. Orientation of the attitude control motors (momentum wheels). The 3 axes are perpendicular to one another and go through the center of mass of the station.

Key: 1. Center of mass of the station.

The thrusters are similar both in construction and in operating characteristics to the propulsion systems of the space ships described previously. They are, however, much less powerful than those described, corresponding to the lesser demands imposed on them (the accelerations caused by them need not be large). They are positioned in such a manner that they can impart an acceleration to the station in any direction.


Partitioning the Space Station into 3 Entities

It would, no doubt, be conceivable to design technical equipment that make possible staying in empty space despite the absence of all materials; however, even the absence of gravity would (at least in a physical sense, probably otherwise also) not present any critical obstacle to the sustenance of life, if the various peculiarities resulting from space conditions are taken into consideration in the manner previously indicated.

However, since the weightless state would be associated in any case with considerable inconveniences and could even perhaps prove to be dangerous to health over very long periods of time, artificial replacement of gravity is provided for in the space station. In accordance with our previous discussion, the force of gravity, being an inertial force, can only be influenced, offset or replaced by an inertial force, more specifically, by centrifugal force if a permanent (stabile) state is to result. This very force allows us to maintain the space station in its vertiginous altitude, so to speak, and to support it there. However, since the latter also leads at the same time to complete compensation of the gravitational state in the space station itself, the centrifugal force now is used again (however, in a different manner) to replace the missing gravitational state.

Basically, this is very easy to accomplish: only those parts of the station in which the centrifugal force and consequently a gravitational state are to be produced must be rotated at the proper speed around their center of mass (center of gravity). At the same time, it is more difficult to satisfy the following requirement: the space traveller must be able to exit and enter the station, connect cables and attach large concave mirrors simply and safely when some parts of the station are rotating. Another requirement is that it be possible also to reposition the entire station not only relative to the sun's rays, but also according to the demands of remote observations.

These conditions lead to a partitioning of the space station into three individual entities: first, the "habitat wheel," in which a manmade gravitational state is continually maintained through rotation, thus offering the same living conditions as exist on Earth; it is used for relaxing and for the normal life functions; second, the "observatory"; and third, the "machine room." While retaining the weightless state, the latter two are only equipped in accordance with their special functions; they provide the personnel on duty with a place for performing their work, but only for a short stay.

However, this partitioning of the space station makes it necessary to apply special procedures in order to compensate for the mutual attraction of the individual objects, because even though this is very slight due to the relative smallness of the attracting masses, the mutual attraction would nevertheless lead to a noticeable approach over a longer period (perhaps in weeks or months) and finally even to the mutual impact of individual objects of the space station. The individual objects, therefore, must either: be positioned as far as possible from one another (at several hundred or thousand meters distance), so that the force of mutual attraction is sufficiently low; from time to time the approach that is occurring nonetheless can be compensated for by means of thrusters, or; be as close as possible to one another and be mutually braced in a suitable manner to keep them separated. In this study, we decided on the first alternative (Figure 94).


The Habitat Wheel

As is generally known, both the velocity of rotation and the centrifugal force at the various points of a rotating object are proportional to the distance from its center of rotation, the axis (Figure 83); i.e., the velocity is that much greater, the further the point in question is distant from the axis and that much less, the closer it is to the axis; it is equal to zero on the theoretical axis of rotation itself.

Figure 83. Velocity of rotation and centrifugal force on a rotating object.

Key: 1. Centrifugal force; 2. Velocity of rotation; 3. Distance from the center of rotation; 4. Center of rotation; 5. Rotating object; 6. Axis of rotation.

Accordingly, the rotating part of the space station must be structured in such a manner that its air lock and the cable connections in the center of the entire structure are in the axis of rotation because the least motion exists at that point, and that those parts, in which a gravitational effect is to be produced by centrifugal force, are distant from the axis on the perimeter because the centrifugal force is the strongest at that point.

Figure 84. The Habitat Wheel. Left: Axial cross section. Right: View of the side constantly facing the sun, without a concave mirror, partially in cross section.

Key: 1. Wheel rim; 2. Well of the staircase; 3. Elevator shaft; 4. Axial segment; 5. Circular corridor; 6. Turnable air lock; 7. Elevator; 8. Bull's eyes with mirrors; 9. Condenser pipes; 10. Evaporation tube; 11. Bull's eye (window); 12. Cable connection.

These conditions are, however, best fulfilled when the station is laid out in the shape of a large wheel as previously indicated (Figures 84, 89 and 90): the rim of the wheel is composed out of cells and has the form of a ring braced by wire spokes towards the axis. Its interior is separated into individual rooms by partitions; all rooms are accessible from a wide corridor going around the entire station. There are individual rooms, larger sleeping bays, work and study areas, mess hall, laboratory, workshop, dark room, etc., as well as the usual utility areas, such as a kitchen, bath room, laundry room and similar areas. All rooms are furnished with modern day comforts; even cold and warm water lines are available. In general, the rooms are similar to those of a modern ship. They can be furnished just like on Earth because an almost normal, terrestrial gravitational state exists in these rooms.

Figure 85. Directional relationships in the habitat wheel.

Key: 1. Direction of the centrifugal force, that is, of apparent gravity; 2. Everything vertical is tilted instead of parallel; 3. "Lowest" region; 4. Partition; 5. Down; 6. Up; 7. Bathtub; 8. The water level is curved instead of straight (flat); 9. Vertical direction; 10. Vertical; 11. Axis of rotation (center) of the habitat wheel; 12. "Highest" point.

However, to create this gravitational state, the entire station, assuming a diameter of 30 meters, for example, must rotate in such a manner that it performs a complete rotation in about 8 seconds, thus producing a centrifugal force in the rim of the wheel that is just as large as the gravitational force on the Earth's surface.

While the force of gravity is directed towards the center of mass, the centrifugal force, on the other hand, is directed away from the center. Therefore, "vertical" in the habitat wheel means the reverse of on Earth: the radial direction from the center (from the axis of rotation) directed outward (Figure 85). Accordingly, "down" now points towards the perimeter and at the same time to the "lowest" part, while "up" now points towards the axis and at the same time to the "highest" point of this manmade celestial body. Taking its smallness into account, the radial orientation of the vertical direction, which in most cases is irrelevant on the Earth due to its size, now clearly becomes evident in the space station. The consequence of this is that all "vertical" directions (such as those for human beings standing erect, the partitions of the rooms, etc.) are now convergent instead of parallel to one another, and everything "horizontal" (e.g., water surface of the bathtub) appears curved instead of flat (see Figure 85).

A further peculiarity is the fact that both the velocity of rotation and the centrifugal force, as a result of their decrease towards the center of rotation, are somewhat less at the head of a person standing in the habitat wheel than at his feet (by approximately 1/9 for a wheel diameter of 30 meters) (Figure 83). The difference in the centrifugal forces should hardly be noticeable, while that of the velocities of rotation should be noticeable to some degree, especially when performing up and down (i.e., radial) movements, such as lifting a hand, sitting down, etc.

Figure 86. a) Top view onto the external door of the rotating air lock of the habitat wheel. b) Axial cross section through the rotating air lock of the habitat wheel.

(See Figure 84 and the text.)

The ball bearings are designed in such a manner that they allow movement in the direction of the axis through which closing and/or releasing is possible of the external air seal which connects the air lock airtight to the inside of the habitat wheel when the inside door is open.

Key: 1. Rotation of the habitat wheel; 2. Rotation of the air lock; 3. Axial segment; 4. Inside door; 5. To the air pump; 6. Air intake valve; 7. External air seal; 8. Motor pinion gear; 9. Gear on the rotor of the lock; 10. Outside door; 11. Ball bearing; 12. Rotating air lock, movement in the axial direction.

However, all of these phenomena make themselves felt that much less, the larger the diameter of the wheel. In the previously selected case (30 meters in diameter), only a slight effect would be perceptible.

Since the equipment for connecting to the outside is installed in near the axis (because at that point the least motion exists!), the axial segment forms a kind of "entrance hall" of the entire station. This segment has a cylindrical shape. At its ends (near those points where it is penetrated by the theoretical axis of rotation), the air lock is positioned on one side and the cable connection on the other side (Figure 84, S and K).

The air lock is made rotatable in order to ease the transition between the rotational movement of the habitat wheel and the state of rest of outer space (Figure 86). When "outgoing," the air lock is stationary with respect to the habitat wheel (thus, it is rotating with respect to outer space). People can, therefore, move easily out of the habitat wheel into the air lock. Then, the latter begins to rotate by electrical power opposite to the direction of rotation of the habitat wheel until it reaches the same rotational speed as the habitat wheel. As a result, the air lock is stationary in relation to outer space and can now be departed just as if the habitat wheel were not even rotating. The process is reversed for "incoming." With some training, rotating the air lock can, however, be dispensed with because the habitat wheel rotates only relatively slowly at any rate (one complete revolution in approximately 8 seconds in the previously assumed case with a 30 meter diameter of the wheel).

Even the cable connection at the other side of the axle segment is designed in a basically similar manner in order to prevent the cable from becoming twisted by the rotation of the habitat wheel. For this reason, the cable extends out from the end of a shaft (Figure 87), which is positioned on the theoretical axis of rotation of the habitat wheel and is continually driven by an electrical motor in such a manner that it rotates at exactly the same speed as the habitat wheel, but in the opposite direction. As a result, the shaft is continually stationary in relation to outer space. The cable extending from the shaft cannot, in fact, be affected by the rotation of the habitat wheel.

Figure 87. A. Top view onto the cable connection of the habitat wheel. B. Axial cross section through the cable connection of the habitat wheel.

(See Figures 84, K, and the text.)

Key: 1. Rotation of the habitat wheel; 2. Rotation of the shaft; 3. Cable; 4. Shaft; 5. Compound cable; 6. Ball bearings; 7. Passageways sealed airtight; 8. Vacuum;

9. Sliding contact rings; 10. Pressurized; 11. High and low voltage lines on the inside of the habitat wheel;

12. Heating tube.

Stairs and electrical elevators installed in tubular shafts connect the axial segment and the rim of the wheel. These shafts run "vertically" for the elevators, i.e., radially (Figure 84, A). On the other hand, for the stairs, which must be inclined, the shafts are taking the divergence of the vertical direction into account curved along logarithmic spirals that gradually become steeper towards "up" (towards the center) (Figures 88 and 84, T) because the gravitational effect (centrifugal force) decreases more and more towards that point. By using the stairs and/or elevators in an appropriately slow manner, the transition can be performed gradually and arbitrarily between the gravitational state existing in the rim of the wheel and the absence of gravity in outer space.

Figure 88. Well of the living wheel staircase.

Key: 1. Axial beam; 2. Elevator shaft; 3. Rim of the wheel; 4. Well of the staircase; 5. Railing; 6. Logarithmic spiral with a slope of 30.

Supplying the habitat wheel with light, heat, air and water takes place in the fashion previously specified in general for the space station by employing the engineering equipment described there. The only difference being that the wall of the wheel rim always facing the sun also acts to heat the habitat wheel; for this reason, this wall is colored dull black (Figures 89 and 84), in contrast to the otherwise completely highly polished external surfaces of the station. A small solar power plant sufficient for emergency needs of the habitat wheel is also available.

Figure 89. Total view of the side of the habitat wheel facing the sun. The center concave mirror could be done away with and replaced by appropriately enlarging the external mirror.

All storage rooms and tanks for adequate supplies of air, water, food and other materials, as well as all mechanical equipment are in the wheel rim. The concave mirrors associated with this equipment and the dull black colored steam generator and condenser pipes are attached to the habitat wheel on the outside in an appropriate manner and are rotating with the habitat wheel (Figures 84, 89 and 90).

Figure 90. Total view of the shadow side of the habitat wheel.

Finally, attitude control motors and thrusters are provided; besides the purposes previously indicated, they will also generate the rotational motion of the habitat wheel and stop it again; they can also control the rate of rotation.


The Observatory and Machine Room

The decisive idea for the habitat wheel, creating living conditions as comfortable as possible must be of secondary importance for the observatory and machine room compared to the requirement for making these systems primarily suitable for fulfilling their special tasks. For this reason, eliminating the weightless state is omitted, as noted previously, for these systems.

Primarily, it is important for the observatory (Figure 91) that any arbitrary orientation in space, which is necessitated by the observations to be carried out, can easily be assumed. It must, therefore, be completely independent of the sun's position; consequently, it may not have any of the previously described equipment that is powered by solar radiation. For this reason, ventilation and the simultaneous heating of the observatory as well as its electrical supply take place from the machine room; consequently, both units are connected also by a flexible tube as well as a cable (Figures 91 and 92). Nevertheless, a precaution is taken to ensure that the ventilation of the observatory can also be carried out automatically in an emergency by employing purification cartridges, as is customary in modern diving suits.

Figure 91. An example of the design of an observatory. Taking into account the over-pressure of 1 atm. existing inside, the observatory resembles a boiler. The air lock, two electrical cables (left), the flexible air tube (right) and the Bull's eyes can be seen.

The observatory contains the following equipment: primarily, remote observation equipment in accordance with the intended purpose of this unit and, furthermore, all controls necessary for remote observations, like those needed for the space mirror (see the following). Finally, a laboratory for performing experiments in the weightless state is also located in the observatory.

The machine room is designed for housing the major mechanical and electrical systems common to the entire space station, in particular those that serve for the large-scale utilization of the sun's radiation. Primarily, it contains the main solar power plant including storage batteries. Furthermore, all of the equipment in the large transmission station is located here, and finally, there is a ventilation system, which simultaneously supplies the observatory.

Figure 92. The flexible tube for connecting the observatory with the ventilation system in the machine room.

Key: 1. To the machine room; 2. Spent air; 3. Regenerated and heated air; 4. To the observatory.

Collecting solar energy takes place through a huge concave mirror firmly connected to the machine room (Figure 93), in whose focal point the evaporating and heating pipes are located, while the condenser and cooling pipes are attached to its back side. The orientation of the machine room is, therefore, determined beforehand: the concave mirror must always squarely face the sun.

Figure 93. Example of the design of the machine room shown in the axial cross section.

Key: 1. Condenser pipes; 2. Machine room; 3. Air lock; 4. Evaporating pipes.

Lighting of both the observatory and machine room is achieved in the manner already described in general for the space station. All external surfaces of the units are highly polished in order to reduce the cooling effect. Finally, both units are also equipped with attitude control motors and thrusters.

Kitchens, water purification systems, washing facilities, and similar systems are missing, however, because of the very troublesome properties of liquids in the weightless state. The habitat wheel is available for eating and personal hygiene. Necessary food and beverages in the observatory and machine room must be brought in from the habitat wheel, prepared in a manner compatible with the weightless state.


Providing for Long Distance Communications and Safety

Communicating among the individual components of the space station takes place in the manner previously indicated either through signalling with lights or by either radio or wire. Accordingly, all three substations are equipped with their own local radio stations and, furthermore, are connected to one another by cables that include electric power lines.

Finally, each one of the three substations carries reserve supplies of food, oxygen, water, heating material and electricity (stored in spare batteries) in such a manner that it can house the entire crew of the space station for some time in an emergency, if, for instance, each of the other two substations should become unusable at the same time through an accident. In this manner, the tripartitioning of the space station, originally chosen for technical reasons, also contributes considerably to safety. In order to enhance the latter still further, provisions are mace to ensure that each substation not only can communicate with the ground through the central radio station, but also independently via its own flashing mirror system.


Partitioning the Space Station into 2 Entities

Instead of 3 parts, the space station could also be partitioned into only 2 entities by combining the habitat wheel and the machine room. Basically, this would be possible because the orientation in outer space for these two units is determined only by the direction of the sun's rays; more specifically, it is determined in the same manner.

If the mirror of the machine room is to be exempted from participating in the (for its size) relatively rapid rotation of the habitat wheel, then, for example, the habitat wheel and machine room (including its mirror) could both be rotated around a common axis of rotation- but in a reverse sense. Or the habitat wheel and machine room could be completely integrated into one structure, and the large mirror of the machine room alone could be rotated around its axis of rotation, also in an opposite direction. Other methods could also be employed.

The advantages of a two-component space station would be as follows:

Movement within the space station is simplified.

The provisions necessary in a separated partitioning to compensate for the mutual attraction between habitat wheel and machine room are no longer needed.

The rotational motion of the habitat wheel can now be produced, changed and stopped through motor power instead of thrusters without any expenditure of propellants because now the entire machine room and/or its large mirror are available as a "counter mass" for this purpose (consequently, the reverse rotational direction of the mirror).

These advantages are countered by the disadvantage that significant design problems result, but these are solvable. We want to refrain from examining any further this partitioning of the space station in more detail here in order not to complicate the picture obtained of it up to this point.


The Space Suit

Both for assembly and operation of the space station (moving between individual entities and to and from the space ships, performing varying tasks, etc.) it is necessary to be able to remain outside of the enclosed rooms in open space. Since this is only possible using the previously mentioned space suits, we have to address these suits in more detail.

As previously explained, they are similar to the modern diving and/or gas protective suits. But in contrast to these two suits, the space suit garment must not only be airtight, resistant to external influences and built in such a manner that it allows movement to be as unrestricted as possible; additionally, it must have a large tensile strength because a gas pressure (overpressure of the air in relation to empty space) of one full atmosphere exists within the garment. And moreover, it should be insensitive to the extremely low temperatures that will prevail in empty space due to heat loss by thermal emission. The garment must neither become brittle nor otherwise lose strength. Without a doubt, very significant requirements will be imposed on the material of such a space suit.

In any case, the most difficult problem is the protection against cold; or, more correctly stated, the task of keeping the loss of heat through radiation within acceptable limits. One must attempt to restrict the capability of the garment to radiate to a minimum. The best way of attaining this goal would be to give the suit in its entirety a high polish on the outside. It would then have to be made either completely of metal or at least be coated with a metal. However, an appropriately prepared flexible material insensitive to very low temperatures would perhaps suffice as a garment, if it is colored bright white on the outside and is as smooth as possible.

Nevertheless, the advantage of a material of this nature may not be all that great as far as the freedom of movement is concerned, because even when the garment used is flexible, it would be stiff since the suit is inflated (taut) as a result of the internal overpressure such that special precautions would have to be taken to allow sufficient movement, just as if the garment were made of a solid material, such as metal. The all metal construction would appear to be the most favorable because much experience from the modern armor diving suits is available regarding the method of designing such stiff suits; furthermore a structure similar to flexible metal tubes could possibly also be considered for space use.

We will, therefore, assume that the space suits are designed in this manner. As a result of a highly polished external surface, their cooling due to thermal emission is prevented as much as possible. Additionally, a special lining of the entire suit provides for extensive thermal insulation. In case cooling is felt during a long stay on the outside, it is counteracted through in-radiation from mirrors on the shadow side of the space suit. Supplying air follows procedures used for modern deep sea divers. The necessary oxygen bottles and air purification cartridges are carried in a metal backpack.

Since voice communication through airless space is possible only via telephones and since a connection by wires would be impractical for this purpose, the space suits are equipped with radio communication gear: a small device functioning as sender and receiver and powered by storage batteries is also carried in the backpack for this purpose. The microphone and the head phone are mounted firmly in the helmet. A suitably installed wire or the metal of the suit serves as an antenna. Since each individual unit of the space station is equipped for local radio communication, spacefarers outside the station can, therefore, speak with each other as well as with the interior of any of the space station units, just like in the airfilled space however, not by means of air waves, but through ether waves.

For special safety against the previously described danger of "floating away into outer space" threatened during a stay in the open, the local radio stations are also equipped with very sensitive alarm devices that respond, even at great distances, to a possible call for help from inside a space suit.

In order to prevent mutual interference, various wavelengths are allocated to the individual types of local radio communications; these wavelengths can be tuned in easily by the radio devices in the space suits. Small handheld thrusters make possible random movements. Their propellant tanks are also located in the backpack along with the previously described devices.


The Trip to the Space Station

The traffic between the Earth and the space station takes place through rocket-powered space ships, like those described in general in the first part of this book. It may complete the picture to envision such a trip at least in broad outlines:

The space ship is readied on the Earth. We enter the command room, a small chamber in the interior of the fuselage where the pilot and passengers stay. The door is locked airtight from the inside. We must lie down in hammocks. Several control actions by the pilot, a slight tremor in the vehicle and in the next moment we feel as heavy as lead, almost painfully the cords of the hammocks are pressed against the body, breathing is labored, lifting an arm is a test of strength: the ascent has begun. The propulsion system is working, lifting us up at an acceleration of 30 m/sec2, and causing us to feel an increase of our weight to four times its normal value. It would have been impossible to remain standing upright under this load.

It does not take long before the feeling of increased gravity stops for a moment, only to start again immediately. The pilot explains that he has just jettisoned the first rocket stage, which is now spent, and started the second stage. Soon, new controlling actions follow: as explained by the pilot, we have already attained the necessary highest climbing velocity; for this reason, the vehicle was rotated by 90, allowing the propulsion system to act now in a horizontal direction in order to accelerate us to the necessary orbital velocity.

Very soon, we have attained this velocity. Only some minutes have elapsed since launch; however, it seems endless to us, [given] that we had to put up with the strenuous state of elevated gravity. The pressure on us is gradually diminishing. First we feel a pleasant relief; then, however, an oppressive fear: we believe we are falling, crashing into the depths. The brave pilot attempts to calm us: he has slowly turned the propulsion system off. Our motion takes place now only by virtue of our own kinetic force, and what was sensed as free fall is nothing other than the feeling of weightlessness, something that we must get used to whether we like it or not. Easier said than done; but since we have no other choice, we finally succeed.

In the meantime, the pilot has acutely observed with his instruments and consulted his tables and travel curves. Several times the propulsion system was restarted for a short time: small orbital corrections had to be made. Now the destination is reached. We put on space suits, the air is vented from the command room, the door is opened. Ahead of us at some distance we see something strange, glittering in the pure sunlight like medallions, standing out starkly in the deep black, starfilled sky: the space station (Figure 94).

Figure 94. The complete space station with its 3 units, seen through the door of a space ship. In the background-35,900 km distant-is the Earth. The center of its circumferential circle is that point of the Earth's surface on the equator over which the space station continually hovers (see Pages 107109). As assumed in this case, the space station is on the meridian of Berlin, approximately above the southern tip of Cameroon.

However, we have little time to marvel. Our pilot pushes away and floats toward the space station. We follow him, but not with very comfortable feelings: an abyss of almost 36,000 km gapes to the Earth! For the return trip, we note that our vehicle is equipped with wings. These were carried on board in a detached condition during the ascent and have now been attached, a job presenting no difficulties due to the existing weightlessness.

We reenter the command room of the space ship; the door is closed; the room is pressurized. At first the propulsion system begins to work at a very low thrust: a slight feeling of gravity becomes noticeable. We must again lie down in the hammocks. Then, little by little more thrusters are switched on by the pilot, causing the sensation of gravity to increase to higher and higher levels. We feel it this time to be even heavier than before, after we had been unaccustomed to gravity over a longer period. The propulsion system now works at full force, and in a horizontal but opposite direction from before; our orbital velocity and consequently the centrifugal force, which had sustained us during the stay in the space station, must be decreased significantly to such a degree that we are freely falling in an elliptical orbit towards the Earth. A weightless state exists again during this part of the return trip.

In the meantime, we have come considerably closer to the Earth. Gradually, we are now entering into its atmosphere. Already, the air drag makes itself felt. The most difficult part of this trip is beginning: the landing. Now by means of air drag, we have to brake our travel velocity-which has risen during our fall to Earth up to around 12 times the velocity of a projectile so gradually that no overheating occurs during the landing as a result of atmospheric friction.

As a precautionary measure, we have all buckled up. The pilot is very busy controlling the wings and parachutes, continuously determining the position of the vehicle, measuring the air pressure and outside temperature, and performing other activities. For several hours, we orbit our planet at breakneck speed: in the beginning, it is a headdown flight at an altitude of approximately 75 km; later, with a continual decrease of the velocity, we approach the Earth more and more in a long spiral and, as a result, arrive in deeper, denser layers of air; gradually, the terrestrial feeling of gravity appears again, and our flight transitions into a normal gliding flight. As in a breakneck race, the Earth's surface rushes by underneath: in only half hours, entire oceans are crossed, continents traversed. Nevertheless, the flight becomes slower and slower and we come closer to the ground, finally splashing down into the sea near a harbor.


Special Physical Experiments

And now to the important question: What benefits could the described space station bring mankind! Oberth has specified all kinds of interesting proposals in this regard and they are referenced repeatedly in the following. For example, special physical and chemical experiments could be conducted that need large, completely airless spaces or require the absence of gravity and, for that reason, cannot be performed under terrestrial conditions. Furthermore, it would be possible to generate extremely low temperatures not only in a simpler fashion than on the Earth, but absolute zero could also be approached much more closely than has been possible in our refrigeration laboratories to date, approximately 1 absolute, that is, 272 Celsius, has been attained there because, besides the technique of helium liquefaction already in use for this purpose, the possibility of a very extensive cooling by radiating into empty space would be available on the space station.

The behavior of objects could be tested under the condition of an almost complete absence of heat, something that could lead to extremely valuable conclusions about the structure of matter as well as about the nature of electricity and heat, as the experiments of that type carried out previously in our refrigeration laboratories would lead us to expect. Probably even practical benefits perhaps even to the grandest extent would also result as a further consequence of these experiments. In this context, we could think of the problem, for example, of discovering a method for using the enormous amounts of energy bound up in matter.

Finally, in consideration of the special potentials offered by a space station, the problems of polar light, of cosmic rays, and of some other natural phenomena not yet fully explained could be brought to a final clarification.


Telescopes of Enormous Size

As has been previously explained, due to the absence of an atmosphere no optical barrier exists in empty space to prevent using telescopes of unlimited sizes. But also from the standpoint of construction, conditions are very favorable for such instruments due to the existing weightlessness. The electrical power necessary for remotely controlling the instruments and their components is also available in the space station.

Thus, for example, it would be possible to build even kilometer- long reflecting telescopes simply by positioning electrically adjustable, parabolic mirrors at proper distances from the observer in empty space. These and similar telescopes would be tremendously superior to the best ones available today on Earth. Without a doubt, it can be stated that almost no limits would exist at all for the performance of these instruments, and consequently for the possibilities of deep space observations.


Observing and Researching the Earth's Surface

Everything even down to the smallest detail on the Earth's surface could be detected from the space station using such powerful telescopes. Thus, we could receive optical signals sent from Earth by the simplest instruments and, as a result, keep research expeditions in communication with their home country, and also continually follow their activities. We could also scan unexplored lands, determining the make up of their soil, obtaining general information about their inhabitation and accessibility and, as a result, accomplish valuable preliminary work for planned research expeditions, even making available to these expeditions detailed photographic maps of the new lands to be explored.

This short description may show that cartography would be placed on an entirely new foundation, because by employing remote photography from the space station not only entire countries and even continents could be completely mapped in a simple fashion, but also detailed maps of any scale could be produced that would not be surpassed in accuracy even by the most conscientious work of surveyors and map makers. Land surveys of this type would otherwise take many years and require significant funding. The only task remaining then for map makers would be to insert the elevation data at a later date. Without much effort, very accurate maps could thus be obtained of all regions of the Earth still fairly unknown, such as the interior of Africa, Tibet, North Siberia, the polar regions, etc.

Furthermore, important marine routes at least during the day and as far as permitted by the cloud cover could be kept under surveillance in order to warn ships of impending dangers, such as floating icebergs, approaching storms and similar events, or to report ship accidents immediately. Since the movement of clouds on more than one-third of the entire Earth's surface could be surveyed at one time from the space station and at the same time cosmic observations not possible from the Earth could be performed, an entirely new basis should also result for weather forecasting.

And not the least important point is the strategic value of the possibilities of such remote observations: spread out like a war plan, the entire deployment and battle area would lie before the eyes of the observer in the space station! Even when avoiding every movement during the day as far as possible, the enemy would hardly be successful in hiding his intentions from such "Argus eyes."


Exploring the Stars

The most exciting prospects for remote observation from the space station exist for astronomy, because in this case, besides the possibility of using large telescopes at will, there are two other advantages: the radiations from the stars arrive completely unweakened and undistorted, and the sky appears totally black. Thus, for example, the latter condition would permit carrying out all those observations of the sun that can be performed on the Earth only during a total solar eclipse by simply occulting the solar disk using a round black screen.

Our entire solar system including all its planets, planetoids, comets, large and small moons, etc. could be studied down to the smallest detail. Even both ("inner") planets, Venus and Mercury, which are close to the sun could be observed just as well as the more distant ("outer") planets, observations that are not possible from the Earth due to dawn and dusk, a problem already mentioned. Therefore, the surfaces of at least all the near celestial bodies (Moon, Venus, Mars, Mercury), as far as they are visible to us, could be precisely studied and topographically mapped by remote photography. Even the question of whether the planets are populated, or at least whether they would be inhabitable, could probably be finally decided in this manner.

The most interesting discoveries would, however, presumably be made in the world of the fixed stars. Many unsolved puzzles at these extreme distances would be solved, and our knowledge of the functioning of the world would be considerably enhanced, perhaps even to a degree that it would then be possible to draw conclusions with absolute certainty about the past and the future fate of our own solar system, including the Earth.

Besides their immediate value, all of these research results would also have, however, the greatest significance for the future development of space travel, because when the conditions in those regions of space and on those celestial bodies at which our travel is aiming are exactly known to us, then a trip to outer space would no longer venture into the unknown, and therefore would lose some of its inherent danger.


A Giant Floating Mirror

The potentials of a space station are by no means exhausted with the above descriptions. Based on the condition that for the space station the sun shines unattenuatedly and continuously (disregarding occasional brief passes through the Earth's shadow), benefits could be derived, furthermore, for some technical applications on Earth. From the space station, the sun's radiation even on a large scale could be artificially focused on various regions of the Earth's surface if, as Oberth suggests, giant mirrors were erected that were appropriately built, orbited the Earth in a free orbital path, and hence were suspended above it.

According to Oberth, these mirrors would consist of individual segments, moveable in such a manner that any arbitrary orientation in the plane of the mirror can be remotely assigned to them through electrical signals. By appropriately adjusting the segments, it would then be possible, depending on the need, to spread the entire solar energy reflected by the mirror over wide regions of the Earth's surface or to concentrate it on single points, or finally to radiate it out into space if not being used.

"Space mirrors" of this type would be in a weightless state as a result of their orbital motion; this fact would considerably simplify their manufacture. According to Oberth, a circular network of wires could serve as a frame for their construction and, to this end, could be extended in space through rotation. The individual segments would be attached to the wire mesh and would consist of paper-thin sodium foils. According to Oberth's plans, a mirror of this type with a diameter of 100 km would cost around 3 billion marks and require approximately 15 years for its completion.

Besides this proposal, there would, no doubt, be still other possibilities of constructing a large floating mirror of this type. At smaller diameters of perhaps only several 100 meters, we could certainly succeed in giving the entire mirror such a rigid structure that it could be rotated at will around its center of mass, even in its entirety, by means of control motors, and that arbitrary positional changes could be performed with it.

The electrical energy necessary for controlling mirrors of this type would be available in the space station in sufficient quantity. The actual controls would have to be placed in the observatory and positioned in such a fashion that they could be operated at the same time while performing observations with the giant telescope, making it possible to adjust the mirrors' field of light precisely on the Earth.

The uses of this system would be numerous. Thus, important harbors or airports, large train stations, even entire cities, etc. could be illuminated during the night with natural sunlight, cloud cover permitting. Imagine the amount of coal saved if, for example, Berlin and other cosmopolitan centers were supplied with light in this fashion!

Using very large space mirrors, it would also be possible, according to Oberth, to make wide areas in the North inhabitable through artificial solar radiation, to keep the sea lanes to Northern Siberian harbors, to Spitzbergen, etc. free of ice, or to influence even the weather by preventing sudden drops in temperature and pressure, frosts, hail storms, and to provide many other benefits.


The Most Dreadful Weapon

But like any other technical achievement the space mirror could also be employed for military purposes and, furthermore, it would be a most horrible weapon, far surpassing all previous weapons. It is well known that fairly significant temperatures can be generated by concentrating the sun's rays using a concave mirror (in a manner similar to using a so-called "burning glass"). Even when a mirror has only the size of the human hand, it is possible to ignite a handheld piece of paper or even wood shavings very simply in its focus (Figure 95).

Figure 95. Igniting a piece of wood using a concave mirror.

Key: 1. Sun's rays.

Imagine that the diameter of a mirror of this type is not just 10 cm, but rather several hundreds or even thousands of meters, as would be the case for a space mirror. Then, even steel would have to melt and refractory materials would hardly be able to withstand the heat over longer periods of time, if they were exposed to solar radiation of such an enormous concentration.

Now, if we visualize that the observer in the space station using his powerful telescope can see the entire combat area spread out before him like a giant plan showing even the smallest details, including the staging areas and the enemy's hinterland with all his access routes by land and sea, then we can envision what a tremendous weapon a space mirror of this type, controlled by the observer in orbit, would be!

It would be easy to detonate the enemy's munitions dumps, to ignite his war material storage area, to melt cannons, tank turrets, iron bridges, the tracks of important train stations, and similar metal objects. Moving trains, important war factories, entire industrial areas and large cities could be set ablaze. Marching troops or ones in camp would simply be charred when the beams of this concentrated solar light were passed over them. And nothing would be able to protect the enemy's ships from being destroyed or burned out, like bugs are exterminated in their hiding place with a torch, regardless of how powerful the ships may be, even if they sought refuge in the strongest sea fortifications.

They would really be death rays! And yet they are no different from this lifegiving radiation that we welcome everyday from the sun; only a little "too much of a good thing." However, all of these horrible things may never happen, because a power would hardly dare to start a war with a country that controls weapons of this dreadful nature.


To Distant Celestial Bodies

In previous considerations, we did not leave the confines of the dominant force of the Earth's attraction its "territory in outer space," so to speak. What about the real goal of space flight: completely separating from the Earth and reaching more distant celestial bodies?

Before we examine this subject, a brief picture of the heavenly bodies is provided, seen as a future destination from the standpoint of space travel. In the first place, we must broaden the scope of our usual notions, because if we want to consider the entire universe as our world, then the Earth, which previously appeared to us as the world, now becomes just our "immediate homeland." Not only the Earth! But everything that it holds captive by virtue of its gravitational force, like the future space station; even the Moon must still be considered a part of our immediate homeland in the universe, a part of the "Earth's empire." How insignificant is the distance of about 380,000 km to the Moon in comparison to the other distances in outer space! It is only a thousandth of the distance to Venus and Mars, located next to us after the Moon, and even the Earth together with the Moon's entire orbit could easily fit into the sun's sphere.

The next larger entity in the universe for us is the solar system, with all its various, associated heavenly bodies. These are the 8 large planets or "moving" stars, one of which is our Earth, (Figures 96 and 97) and numerous other celestial bodies of considerably smaller masses: planetoids, periodic comets, meteor showers, etc. Of the planets, Mercury is closest to the sun, followed by Venus, the Earth, Mars, Jupiter, Saturn, Uranus and Neptune, the most distant. Together with the Moon, Venus and Mars are the planets nearest to the Earth.

All of these celestial bodies are continuously held captive to the sun by the effect of gravity; the bodies are continually forced to orbit the sun as the central body in elliptical orbits. The planets together with the sun form the "sun's empire of fixed stars," so to speak. They form an island in the emptiness and darkness of infinite space, illuminated and heated by the sun's brilliance and controlled at the same time by the unshakable power of the sun's gravitational force, and are thus linked in an eternal community. That island is our "extended homeland" within the universe. A realm of truly enormous size: even light needs more than 8 hours to traverse it and it is racing through space at a velocity of 300,000 km per second!

Figure 96. A schematic of the orbits of the 8 planets of our solar system in their relative sizes.

Key: 1. Sun; 2. Mercury; 3. Earth; 4. Neptune.

Figure 97. Enlarged rendition taken from Figure 96 of the orbits of Mars, the Earth, Venus and Mercury.

Key: 1. Earth; 2. Mercury.

And yet, how tiny is this world compared to the incomprehensible distances of the universe, from which those many white hot celestial bodies familiar to us as fixed stars send their shining greetings of radiation. Even the one closest to us, the fixed star Alpha Centauri, is 4.3 light years away; i.e., around 4,500 times as far as the diameter of the entire solar system! All of the others are still many more light years away from us, most of them hundreds and thousands of light years. And if there are fixed stars closer to us that are already burnt out, then we are unaware of them in the eternal darkness of empty space.

From this discussion, it can be seen that only those heavenly bodies belonging to the solar system can be considered for the trip to alien celestial bodies, at least according to the views held today.


The Technology of Space Travel

Just exactly how the long trip through outer space can be achieved has already been indicated at the beginning of this book: in general, in free orbits around those celestial bodies in whose gravitational field the trip is proceeding. Within its realm, the sun must consequently be continually orbited in some free orbit if a space ship is to avoid falling victim to its gravitational force and crashing into its fiery sea.

However, we do not have to take any special precautions as long as we stay close to the Earth or to another heavenly body of the solar system. After all, these bodies orbit the sun in their own free orbits, as do all bodies belonging to it. At the velocity of the Earth (30,000 meters per second), the Moon, for example, also circles the sun, as will our future space station (both as satellites of the Earth). As a result, the sun's gravitational force loses its direct effect on those two satellites ("stable state of floating" compared to the sun).

Only when the space ship moves further away from the immediate gravitational region of a celestial body circling the sun would the sun have to be orbited in an independent free orbit. If, for example, the trip is to go from the Earth to another planet, then, based on previous calculations, both the course of this independent orbit and the time of departure from the Earth must be selected in such a fashion that the space ship arrives in the orbit of the destination planet approximately at the time when the planet also passes through the encounter point.

If the space vehicle is brought in this fashion into the practical effective range of gravity of the destination celestial body, then the possibility exists either to orbit the body in a free orbit as a satellite as often as desired or to land on it. Landing can, if the celestial body has an atmosphere similar to that of the Earth, occur in the same fashion as previously discussed for the Earth (Hohmann's landing manoeuver, Figures 44 and 45). If, however, a similar atmosphere is absent, then the landing is possible only by reaction braking, that is, by operating the propulsion system opposite to the direction of free fall during landing (Figure 37).

To travel to another celestial body within the solar system after escape from the original body, the orbital motion, previously shared with this body around the sun, must be altered by using the propulsion system to such an extent that the space ship enters an independent orbit around the sun, linking its previous orbit with that of the other celestial body. To implement this in accordance with the laws of celestial mechanics, the original orbital movement would have to be accelerated if the vehicle (according to the position of the target body) is to move away from the sun (Figure 98), and to be decelerated if it is to approach it. Finally, as soon as the destination is reached, the motion maintained in the "transfer orbit" must be changed into the motion that the vehicle must have as the new celestial body for effecting the orbiting or landing maneuver. The return trip would occur in the same fashion. It can be seen that repeated changes of the state of motion are necessary during a long-distance trip of this nature through planetary space. The changes would have to be produced through propulsion with an artificial force and, therefore, would require an expenditure of propellants, a point previously mentioned at the beginning of this book. As determined mathematically by Hohmann, the propellant expenditure reaches a minimum when the orbits of the original celestial body and that of the destination body are not intersected by the transfer orbit of the vehicle, but are tangential to it (touch it) (Figure 99). Nevertheless, the required amounts of propellant are not insignificant.

Besides the points discussed above, there are additional considerations if the destination heavenly body is not to be orbited, but is supposed to be landed on. These considerations are all the more important the greater the mass and consequently the gravitational force of the destination planet are, because the reascent from the destination planet when starting the return trip requires, as we already know from the discussion of the Earth, a very significant expenditure of energy. Additionally, if braking must be performed during the landing by propulsion in the absence of an appropriate atmosphere (reaction braking), then a further, significant increase of the amount of necessary propellants results.

Figure 98. If the motion of a freely orbiting body is accelerated, then it expands its original orbit and moves away from the center of gravity. If the motion is decelerated, then the body approaches the center of gravity by contracting its orbit.

Key: 1. Acceleration and, therefore, increasing distance; 2. Orbiting body (e.g., the Earth); 3. Decelerating and, therefore, approaching; 4. Center of gravity (e.g., the sun); 5. Original orbit.

Figure 99. Tangential and intersecting transfer orbits in which the space vehicle must move in order to reach an alien celestial body within the solar system. The numbers in the figure indicate the following: 1. the orbit of the original body; 2. the orbit of the destination celestial body. The distance of the transfer orbit marked by heavy lines is that part of the orbit which the vehicle actually travels through.

Key: A. Sun; B. Transfer orbit.


The propellants must be carried on board from the Earth during the outward journey, at least for the initial visit to another planet, because in this case we could not expect to be able to obtain the necessary propellants from the planet for the return trip.


Launching from the Earth's Surface

If a trip of this nature were launched directly from the Earth's surface, this entire amount of propellant would have to be first separated from the Earth (by overcoming its gravitational force). According to what was stated previously, an extraordinary expenditure of energy is necessary for this purpose.

For the present case, at least with the efficiencies of currently available propellants, the amount to be carried on board would constitute such a high fraction of the total weight of the vehicle that it could hardly be built.

The only visit to a celestial body that could probably be undertaken directly from the Earth's surface with propellants known to date, would be an orbiting of the Moon for exploring its surface characteristics in more detail, in particular, the side of the Moon that continually faces away from the Earth. During this trip, the space ship could also be "captured" by the Moon, so that it would circle the Moon as often as necessary in a free orbit as a moon of the Moon. The amount of propellants necessary for this effort would not be much greater than for a normal ascent from the Earth up to escape velocity.


The Space Station as a Base for Travel into Deep Space

The conditions, however, would be considerably more favorable if a depot for propellants appropriately suspended high over the Earth and continuously circling it in a free orbit was built, as Oberth suggests, and if the trip was started from this depot instead of from the Earth's surface, because in that case only a modest expenditure of energy would be necessary for a complete separation from the Earth, and the vehicle need not, therefore, be loaded with the propellants necessary for the ascent from the Earth. It would have to carry on board only slightly more than the amount necessary for the deep space trip itself.

Since the depot would be in a weightless state as a result of its free orbital motion, the propellants could simply be stored there freely suspended in any amount and at any place. Protected against the sun's rays, even oxygen and hydrogen would remain solidly frozen for an indefinite time. Their resupply would have to be accomplished by a continuous space ship shuttle service either from the Earth where the propellants (at least liquid oxygen and hydrogen) could be produced, for example, in large power plants powered by the heat of the tropical seas; or from the Moon, as Max Valier suggests. This method would be particularly advantageous, because since the mass and consequently the gravitational force of the Moon are considerably smaller than those of the Earth, the expenditure of energy necessary for the ascent and consequently for the propellant supply for that ascent would be significantly less. However, this assumes that the required raw materials would, in fact, be found on the Moon, at least water (in a icelike condition, for instance) because it can be decomposed electrolytically into oxygen and hydrogen, the energy for this process being provided by a solar power plant. Unfortunately, the probability for this is not all that high.

If, however, this should be possible, then even the Moon, according to Hohmann's recommendation, could be used as a starting point for travel into deep space; that is, the propellant depot could be built on the Moon. Despite many advantages of this idea, Oberth's recommendation of a freely suspended depot appears to be the better one, because the complete separation from the gravitational field of the Earth (including the Moon) would require considerably less expenditure of energy from a depot of this nature. More specifically, it would certainly be the most advantageous from an energy economics point of view to build the depot one or more millions of kilometers away from the Earth, especially if the propellants must be supplied from the Earth. We want, however, to build the depot at our space station, and thus make it a transportation base, because it is already equipped with all facilities necessary for this purpose.

Of this equipment, giant telescopes, among others, would be particularly valuable because thanks to their almost unlimited capabilities they would not only make it possible to study in detail the celestial destinations from a distance, a point previously described. The space station could probably keep the space ship under constant surveillance during a large part of its trip, in many cases perhaps even during the entire trip, and could remain in at least one-way communications with it through light signals to be emitted at specific times by the space ship. Thus, the space station, besides satisfying the many assignments already discussed, would be able to satisfy those that assist not only in preparing for actual travel into the universe but also serve as a basis for the entire traffic into outer space.


The Attainability of the Neighboring Planets

Hohmann has studied in detail the problem of travelling to other celestial bodies. According to his results, the long-distance trip would last 146 days from the Earth to Venus and 235 days to Mars, expressed in a terrestrial time scale. A round trip including a flyby of both Venus and Mars at the relatively small distance of approximately 8 million kilometers could be carried out in about 1.5 years. Almost 2.25 years would be necessary for a visit to Venus with a landing, including a stay there of 14.5 months and the two-way travel time.

Assume now the following: in the sense of our previous considerations, the trip would start from the space station, so that only a modest amount of energy would be necessary for the complete separation from the Earth's gravitational field; the return trip would take place directly to the Earth's surface, so that no propulsive energy would have to be expended, because in this case the descent could be controlled by using only air drag braking. The load to be transported would be as follows: 2 people including the supplies necessary for the entire trip, and all instruments required for observation and other purposes.

It then follows from Hohmann's calculations that the vehicle in a launch-ready condition, loaded with all propellants necessary for traveling there and back, would have to weigh approximately the following: 144 tons for the described round trip with a flyby near Venus and Mars, of which 88% would be allocated to the propellants, 12 tons for the first landing on the Moon, 1350 tons for a landing on Venus and 624 tons for a Mars landing. For the trip to the Moon, 79% of the entire weight of the vehicle would consist of the propellants carried on board, but approximately 99% for the trips to Venus and Mars. A 4,000 meter per second exhaust velocity was assumed in these cases.

It is obvious that the construction of a vehicle that has to carry amounts of propellants on board constituting 99% of its weight would present such significant engineering difficulties that its manufacture would initially be difficult to accomplish. For the present, among our larger celestial neighbors, only the Moon would, therefore, offer the possibility of a visit with a landing, while the planets could just be closely approached and orbited, without descending to them. Nevertheless one can hope that we will finally succeed in the long run probably by employing the staging principle explained in the beginning even with technologies known today in building space rockets that permit landings on our neighboring planets.

With the above, and when considering the present state of knowledge, all possibilities are probably exhausted that appear to present themselves optimistically for space ship travel. The difficulties would be much greater confronting a visit to the most distant planets of the solar system. Not only are the distances to be travelled to those destinations much longer than the ones previously considered, but since all of these celestial bodies have a far greater distance from the sun than the Earth, the sun's gravitational field also plays a significant role in their attainability. Because if, for example, we distance ourselves from the sun (i.e, "ascend" from it), then in the same fashion as would be necessary in the case of the Earth's gravitational field, the sun's gravitational field must be overcome by expending energy, expressed as the change of the orbital velocity around the sun, and the distance from its center, as previously discussed. This is required in long- distance travels throughout planetary space.

If, however, we also wanted to descend down to one of these celestial bodies, then enormously large amounts of propellants would be necessary, in particular for Jupiter and Saturn because they have very strong gravitational fields as a result of their immense masses. In accordance with the above discussion, we naturally cannot even think of reaching the fixed stars at the present time, solely because of their enormous distance.


Distant Worlds

This doesn't mean to say that we must remain forever restricted to the Earthly realm and to its nearest celestial bodies. Because, if we succeeded in increasing further the exhaust velocity beyond the 4,000 (perhaps 4,500) meters per second when generating the thrust, the highest attainable in practice at the present time, or in finding a possibility of storing on board very large quantities of energy in a small volume, then the situation would be completely different.

And why shouldn't the chemists of the future discover a propellant that surpasses in effectiveness the previously known propellants by a substantial degree? It might even be conceivable that in the course of time mankind will succeed in using those enormous amounts of energy bound up in matter, with whose presence we are familiar today, and in using them for the propulsion of space vehicles. Perhaps we will someday discover a method to exploit the electrical phenomenon of cathode radiation, or in some other way attain a substantial increase of the exhaust velocity through electrical influences. Even using solar radiation or the decay of radium, among others, might offer possibilities to satisfy this purpose.

In any case, natural possibilities for researchers and inventors of the future are still available in many ways in this regard. If success results from these efforts, then probably more of those alien worlds seen by us only as immensely far away in the star- studded sky could be visited by us and walked on by humans.

An ancient dream of mankind! Would its fulfillment be of any use to us? Certainly, extraordinary benefits would accrue to science. Regarding the practical value, an unambiguous judgement is not yet possible today. How little we know even about our closest neighbors in the sky! The Moon, a part of the Earthly realm, our "immediate homeland" in the universe, is the most familiar to us of all the other celestial bodies. It has grown cold, has no atmosphere, is without any higher life form: a giant rock- strewn body suspended in space, full of fissures, inhospitable, dead-a bygone world. However, we possess significantly less knowledge about that celestial body, observed the best next to the Moon, about our neighboring planet Mars, even though we know relatively much about it in comparison to the other planets.

It is also an ancient body, although considerably less so than the Moon. Its mass and, consequently, its gravitational force are both considerably smaller than that of the Earth. It has an atmosphere, but of substantially lower density than the terrestrial one (the atmospheric pressure on its surface is certainly significantly lower than even on the highest mountain top on Earth). Even water is probably found on Mars. However, a fairly large part of it is probably frozen, because the average temperature on Mars appears to be substantially below that of the Earth, even though in certain areas, such as in the Martian equatorial region, significantly warmer points were detected. The temperature differences between night and day are considerable due to the thinness of the atmosphere.

The most unique and most frequently discussed of all Martian features are the so-called "Martian canals." Even though in recent times they have been considered mostly as only optical illusions, it is still unclear just exactly what they are.

In any case, the present knowledge about Mars does not provide sufficient evidence for a final judgement as to whether this celestial body is populated by any form of life, or even by intelligent beings. For people from Earth, Mars would hardly be inhabitable, primarily because of the thinness of its atmosphere. From a scientific point of view, it would certainly offer an immensely interesting research objective for space travellers. Whether walking on Mars would have any practical value can still not be determined with certainty today; however, this does not appear to be very probable.

It is an altogether different situation with the second planet directly adjacent to us, Venus, the brightly shining, familiar "morning and evening star." Its size as well as its mass and accordingly the gravitational field existing at its surface are only slightly smaller than the Earth's. It also has an atmosphere that should be quite similar to the terrestrial atmosphere, even though it is somewhat higher and denser than the Earth's. Unfortunately, Venus can be observed only with difficulty from the Earth's surface, because it is always closer to the sun and, therefore, becomes visible only at dawn or dusk. As a result, we know very little about its rotation. If Venus rotates in approximately 24 hours roughly like the Earth, a situation assumed by some experts, then a great similarity should exist between Venus and Earth.

In the case of this planet, finding conditions of life similar to terrestrial conditions can be expected with high probability, even if the assumption should be valid that it is continually surrounded by a cloud cover. Because even on Earth, highly developed forms of plant and animal life already existed at a time when apparently a portion of the water now filling the seas and oceans was still gaseous due to the slow cooling of the globe millions of years ago and, therefore, continually surrounded our native planet with a dense cloud cover. In any case, Venus has the highest probability of all the celestial bodies closely known to us of being suitable for colonization and, therefore, of being a possible migration land of the future. Furthermore, since it is nearest to us of all planets, it could be the most likely and tempting destination for space travel.

Mercury offers even more unfavorable conditions for observation than Venus because it is still closer to the sun. Of all the planets it is the smallest, has an atmosphere that is no doubt extremely thin and surface conditions apparently similar to those of the Moon. For this reason and especially due to its short perihelion distance (solar radiation about 9 times stronger than on the Earth!), extremely unfavorable temperature conditions must exist on it. Consequently, Mercury should be considerably less inviting as a destination.

While it was still possible when evaluating the celestial bodies discussed above to arrive at a fairly probable result, our current knowledge about the more distant planets, Jupiter, Saturn, Uranus and Neptune, is hardly sufficient to achieve this. Although we have been able to determine that all of them have dense atmospheres, the question of the surface conditions of these planets is, however, still entirely open: in the cases of Jupiter and Saturn, because they are surrounded by products of condensation (clouds of some kind) so dense that we apparently cannot even see their actual surfaces; and in the cases of Uranus and Neptune, because their great distances preclude precise observation.

Therefore, anything regarding their value as a space flight destination can only be stated with difficulty. But the following condition by itself is enough to dampen considerably our expectations in this regard: a relatively very low average density has been determined for these planets (1/4 to 1/5 of that of the Earth), a condition indicating physical characteristics quite different from those on Earth. It would be perhaps more likely that several of the moons of these celestial bodies (primarily, those of Jupiter would be considered in this connection) offer relatively more favorable conditions. One thing is certain in any case: that their masses are considerably greater than the Earth's and that, therefore, the powerful gravitational fields of these planets would make a visit to them extraordinarily difficult, especially in the cases of Jupiter and Saturn.

Regarding the remaining, varying types of celestial bodies that still belong to the solar system, it can be said with a fair degree of certainty today that we would hardly be able to benefit in a practical sense from a trip to them. We see then that, generally speaking, we should not indulge in too great hopes regarding the advantages that could be derived from other celestial bodies of our solar system. In any case, we know far too little about them not to give free reign to the flight of thoughts in this regard:

Of course, it could turn out that all of these worlds are completely worthless for us! Perhaps, however, we would find on some of them a fertile soil, plant and animal life, possibly of a totally alien and unique nature for us, or perhaps of a gigantic size, as existed on Earth long ago. It would not be inconceivable that we would meet even humans or similar types of life, perhaps even with civilizations very different from or even older than those of our native planet. It is highly probable that life on other planets if it exists there at all is at another evolutionary stage than that on Earth. We would be able then to experience that wonderful feeling of beholding images from the development of our own terrestrial existence: current, actual, living and yet images from an inconceivable, million-year old past or from an equally distant future.

Perhaps we would discover especially valuable, very rare Earthly materials, radium for example, in large, easily minable deposits? And if the living conditions found there are also compatible with long-term human habitation, then perhaps even other celestial bodies will one day be possible as migration lands regardless of how unbelievable this may sound today. That such planets exist among those of our solar system is, however, only slightly probable according to what has been stated previously, with the exception of Venus, as already noted.


Will It Ever be Possible to Reach Fixed Stars?

It would be much more promising, however, if the stars outside of our solar system could also be considered in this context, because the number is enormous even of only those celestial bodies that, since they are in a white-hot state, are visible and, therefore, are known to us as fixed stars. Many of these are similar to our sun and, as powerful centers of gravity, are probably orbited exactly like the sun by a number of small and large bodies of varying types.

Shouldn't we expect to find among these bodies also some that are similar to our planets? Of course, they are too far away for us to perceive them; however, probability speaks strongly for their existence. In fact, the most recent scientific research as one of its most wonderful results has been able to show that the entire universe, even in its most distant parts, is both controlled by the same natural laws and structured from the same material as the Earth and our solar system! At other locations within the universe, wouldn't something similar, in many cases almost the same thing, have to materialize under the same conditions (from the same matter and under the effect of the same laws) as in our case?

It is certainly not unjustified to assume that there would be other solar systems more or less similar to ours in the universe. And among their numerous planets, there surely would be some that are almost similar to the Earth in their physical and other conditions and, therefore, could be inhabited or populated by people from Earth, or perhaps they may already be populated by some living beings, even intelligent ones. At least the probability that this may be the case is significantly greater than if we only consider the relatively few planetary bodies of our solar system.

Yet, would it really be conceivable that those immeasurable distances still separating us even from the closest fixed stars could be traveled by humans, even taking into account the limit that is set by the average life span of a person, completely ignoring the related necessary technical performance of the vehicle?

Let's assume that a goal, which appears enormous even for today's concepts, has been achieved: perfecting the rocket propulsion system to such an extent that an acceleration of approximately 15 m/sec2 could continually be imparted to the space ship over a very long time, even through years. Humans would probably be able to tolerate this acceleration over long periods of time through a gradual accommodation. To travel a given distance in space, it would then be possible to accelerate the vehicle continually and uniformly over the entire first half of its trip, that is, to give it more and more velocity, and to decelerate it in the same way over the second half and consequently to brake it gradually again (Figure 100). With this method, a given distance will be covered in the shortest possibly achievable time with given constant acceleration and deceleration.

Figure 100. Covering a distance when the vehicle is uniformly accelerated over the entire first half of the distance, and similarly the vehicle is decelerated over the second half. The highest velocity of motion resulting from this method is reached at the midpoint.

Key: 1. Midpoint; 2. Accelerated over this distance; 3. Decelerated over this distance; 4. Distance to be traveled; 5. Direction of motion; 6. Velocity curve; 7. Instantaneous velocity.

If the trip now took place to neighboring fixed stars in this manner, then the following travel time would result for the entire round trip (the first visit would have to be a round trip) based on mathematical calculations: 7 years to Alpha Centauri, the star known to be the closest to us, and 10 years to the four fixed stars next in distance; numerous fixed stars could be reached in a total round trip travel time of 12 years.

However, it is quietly assumed here that any velocity, without limitation, is possible in empty ether space. In accordance with the theory of relativity, a velocity greater than the speed of light of 300,000 km per second can never be attained in nature.

If this is taken into account and if it is further assumed that no other obstacle (currently unknown to us, perhaps inherent in the nature of universal world ether) would prevent us from attaining travel velocities approaching the speed of light, then we could, nevertheless, reach the fixed star Alpha Centauri in around 10 years, the four farther stars in 20 years, and a considerable number of neighboring fixed stars presently known to us in 30 years; these figures represent total round trip travel times.

For the one-way trip, which would be of interest for continual traffic, half as much time would suffice. No doubt, trips of such duration would be fairly close to the limit of human endurance; however, they cannot yet be discarded as completely non- implementable, since no fundamental obstacle can, in fact, be seen for reaching the closest fixed stars.

Meanwhile, the question still remains open as to whether vehicles could ever be built having the technical perfection necessary for such performances. However, even this question cannot be answered with an unequivocal no because, as has been pointed out previously, natural phenomena exist that could provide possibilities, such as exploiting the energy bound up in matter by smashing atoms, or utilizing the decay of radium, or cathode radiation, etc.

Admittedly, we are far away today from that goal of completely mastering such natural phenomena to such an extent that we would be able to use them in an engineering sense for space travel purposes! And, we don't know whether this will ever be successful at all.

As far as is humanly possible to predict, the sons of our time will hardly achieve this. Therefore, the fixed stars, which conceal the great secrets of the universe in their immensity, will no doubt remain unreachable for them. Who can say what scientific triumphs and technical potentials future times will bring! Since mankind has now become confident with scientific reasoning, what tremendous progress is achieved today in only a few decades; and what are a hundred, even a thousand years in those eons of human development still ahead of us.

Conquering space! It would be the most grandiose of all achievements ever dreamed of, a fulfillment of the highest purpose: to save the intellectual accomplishments of mankind for eternity before the final plunge into oblivion. Only when we succeed in transplanting our civilization to other celestial bodies, thus spreading it over the entire universe, only when mankind with all its efforts and work and hopes and with what it has achieved in many thousands of years of striving, only when all of this is no longer just a whim of cosmic events, a result of random incidents in eternal nature's game that arise and die down with our little Earth so large for us and yet so tiny in the universe will we be justified to feel as if we were sent by God as an agent for a higher purpose, although the means to fulfill this purpose were created by man himself through his own actions.


The Expected Course of Development of Space Travel

Now let us turn back from these dreams of the future to the reality of the present. It would really be an accomplishment today if we succeeded in lifting an unmanned rocket several 10s or even 100s of kilometers! Even though the problems associated with space travel have been worked out theoretically to some degree thanks to the manyfold efforts of the last few years, almost everything still has to be accomplished from a practical standpoint. Therefore, at the conclusion of this book, possible directions of space travel development are briefly outlined.

The first and most important point in this regard is, without a doubt, the engineering improvement of the rocket engine, the propulsion system of the space ship. This is a task that can be solved only in thorough, unselfish research. It is a problem that should be worked out first and foremost in the experimental laboratories of universities and on the test fields of experienced machine factories.

In connection with the above, experience must be accumulated (at least as far as space rockets for liquid propellants are concerned) in the methods of handling liquefied gases, in particular liquid oxygen, and liquid hydrogen, among others. Furthermore, the behavior of metals at extremely low temperatures should be tested in laboratory experiments in order to determine the substances best suited as construction materials for space ships. Finally, the method of manufacturing propellant tanks will also require detailed studies.

After solving these fundamental engineering issues, the following could then be considered next: to launch unmanned space rockets into the higher layers of the atmosphere or even above them into empty outer space and to let them descend using a parachute, as far as the latter turns out to be achievable.

These experiments will make it possible not only to accumulate the necessary technical experiences concerning rocket technology, but in particular to become familiar also with the laws of aerodynamics at abnormally high velocities and of the laws of heating due to atmospheric friction, data that are of utmost importance for shaping the vehicle itself as well as the parachutes, wings, etc. We will furthermore be able to determine up to what altitudes simple parachute landings are still feasible (taking into consideration the danger of burning the parachute due to atmospheric friction). As a result of these experiments, exact information can finally be obtained about the nature of the higher layers of the Earth's atmosphere, knowledge that forms a most important basis for the further development of space travel, but would also be of great value in many other regards (radio technology, for example).

Firing an unmanned space rocket loaded with flash powder at the Moon, as recommended by many parties, could probably also be attempted as a subsequent step; this would have very little practical value, however.

In parallel with these efforts, we-in order to prepare for the ascent of humans-would have to research the physical tolerance of elevated gravitational effects by performing appropriate experiments using large centrifuges (or carousels) and, furthermore, to create the possibility for remaining in airless space by perfecting the previous methods of supplying air artificially and by testing appropriate space suits in containers made airless and cooled to very low temperatures.

As soon as the results of the previously delineated, preparatory work allow, ascents using simple parachute landings can then be carried out (possibly following previous launchings with test animals) by means of manned space rockets up to altitudes determined beforehand as reliable for such flights. Now we can proceed to equip the vehicles with wings to make them capable of gliding flight landings (Hohmann's landing manoeuver) and consequently for attaining those altitudes from which a simple parachute landing would no longer be feasible.

Experience in the engineering of the rocket propulsion system necessary for building such airplane-like space ships (or expressed in another way: airplanes powered by rocket, that is "recoil airplanes," "rocket airplanes," etc.) and experience with atmospheric friction, air drag, etc. will both have been gained at this time from the previously described preliminary experiments made with unmanned space rockets.

When testing these vehicles, which would be performed by using as extensively as possible previous experiences with aviation, we will first start with relatively short flight distances and altitudes and try to increase these distances and altitudes, gradually at first, then more and more through a corresponding increase of the flight velocities.

As soon as maneuvering with rocket airplanes in general and especially the flight technology necessary at cosmic velocities in the higher, thin layers of air are mastered, the following achievements are practically automatic:

  1. Creating terrestrial "express flight transportation at cosmic velocities," as explained in the beginning of the book; that is, the first practical success of space flight is attained (every ascent of this type not flown above the atmosphere with a gliding flight landing is strictly speaking nothing other than an express flight of this nature);
  2. Making possible the fact that returning space ships can now descend using a gliding flight landing (instead of a simple parachute landing); i.e., the safe return to Earth from any arbitrary altitude is assured as a result, an accomplishment that is of the greatest importance for space flight and signifies an essential precondition for its implementation.

This previously described course of development (first, performing ascents using unmanned space rockets with a simple parachute landing and, only on the basis of the experiences gained during these ascents, developing the rocket airplane) would presumably be more practical than developing this airplane directly from today's airplane, as has been advocated by others, because experiences to be accumulated initially during this development will probably force a certain method of construction for the rocket airplane that may differ considerably from the methods used for airplanes employed today. To arrive, however, at this probable result solely through experiments with airplanes (which are costly), would presumably be significantly more expensive and moreover entail much more danger.

In any case, the most important point is that practical experiments are started as soon as possible. By a gradual increase in the performance of rocket airplanes or airplane-like space ships, more significant horizontal velocities and altitudes will finally be attained in the course of time, until finally free orbital motion above the atmosphere and around the Earth will result. Arbitrarily selecting the orbit will no longer present any difficulties.

Then the potential for creating the previously described space station, that is, achieving the second practical success in the development of space travel, is already given. Also, random high ascents could now be undertaken, and the Moon could eventually be orbited.

Both express flight transportation and the space station are purely terrestrial matters. Now we will strive to realize the additional goals of space flight while using the space station as a transportation control point: walking on the Moon, if possible building a plant on the Moon for producing propellants, orbiting neighboring planets, and other activities that may prove feasible.

Final Remarks

Even if, contrary to expectations, we were not successful soon in attaining in a practical manner the higher exhaust velocities necessary for the goals mentioned above by using sufficiently simple systems, and even if the exhaust velocity could be raised only up to about 2,0003,000 meters per second, then space flight would nevertheless give us in the near future the ability to research thoroughly the Earth's atmosphere up into its highest layers, and especially-as a direct practical benefit-to create the described terrestrial express flight transportation at cosmic velocities, until later times will finally bring the realization of the other goals.

By just accomplishing the above goals, a success would be achieved that would far overshadow everything previously created in the technical disciplines. And it really can no longer be doubted that this would at least be achievable even today with a determined improvement of available engineering capabilities. This will be successful that much sooner the earlier and with the more thorough and serious scientific effort we tackle the practical treatment of the problem, although we must not underestimate the extent of the difficulties that still have to be overcome.

However, the purpose of the present considerations is not an attempt to convince anyone that we will be able tomorrow to travel to other celestial bodies. It is only an attempt to show that traveling into outer space should no longer be viewed as something impossible for humans but presents a problem that really can be solved by technical work. The overwhelming greatness of the goal should make all the roadblocks still standing in its way appear insignificant.


  • The NASA History Series. NASA SP-4026, National Aeronautics and Space Administration, NASA History Office, Washington, DC, Published 1995, HTML revised: December 6, 1996. All rights reserved - http://www.hq.nasa.gov/office/pao/History/SP-4026/cover.html.

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