Up to this point, we have not even pursued the actual purpose of space ship travel. The goal with this purpose initially in mind would now be as follows: to ascend above the Earth's atmosphere into completely empty space, without having to separate completely from the Earth, however. Solely as a result of this effort, tremendous, entirely new vistas would open up.
Nevertheless, it is not sufficient in this regard to be able only to ascend and to land again. No doubt, it should be possible to perform many scientific observations during the course of the trip, during which the altitude is selected so high that the trip lasts days or weeks. A large-scale use of space flight could not be achieved in this fashion, however. Primarily because the necessary equipment for this purpose cannot be hauled aloft in one trip due to its bulk, but only carried one after the other, component- by-component and then assembled at the high altitude.
The latter, however, assumes the capability of spending time, even arbitrarily long periods, at the attained altitude. This is similar, for instance, to a captive balloon held aloft suspended for long periods without any expenditure of energy, being supported only by the buoyancy of the atmosphere. However, how would this be possible in our case at altitudes extending up into empty space where nothing exists? Even the air for support is missing. And still! Even when no material substance is available, there is nevertheless something available to keep us up there, and in particular something very reliable. It is an entirely natural phenomenon: the frequently discussed centrifugal force.
Introductory paragraphs indicated that humans could escape a heavenly body's gravitational effect not only by reaching the practical limit of gravity, but also by transitioning into a free orbit, because in the latter case the effect of gravity is offset by the emerging forces of inertia (in a circular orbit, solely by the centrifugal force, Figure 5), such that a stable state of suspension exists that would allow us to remain arbitrarily long above the heavenly body in question. Now in the present case, we also would have to make use of this possibility.
Accordingly, it is a matter not only of reaching the desired altitude during the ascent, but also of attaining a given orbital velocity exactly corresponding to the altitude in question (and/or to the distance from the Earth's center). The magnitude of this velocity can be computed exactly from the laws of gravitational motion. Imparting this orbital velocity, which in no case would have to be more than around 8,000 meters per second for the Earth, would present no difficulties, as soon as we have progressed to the point where the completed space vehicle is capable of ascending at that rate.
Among the infinitely large number of possible free orbits around the Earth, the only ones having significance for our present purpose are approximately circular and of these the only ones of particular interest are those whose radius (distance from the center of the Earth) is 42,300 km (Figure 54). At an assigned orbiting velocity of 3,080 meters per second, this radius corresponds to an orbital angular velocity just as great as the velocity of the Earth's rotation. That simply means that an object circles the Earth just as fast in one of these orbits as the Earth itself rotates: once per day ("stationary orbit").
Figure 54. Each object orbiting the Earth in the plane of the equator, 42,300 km from the center of the Earth in a circular orbit, constantly remains freely suspended over the same point on the Earth's surface.
Key: 1. Earth's axis; 2. Earth's rotation; 3. Free orbit; 4. Equator; 5. Earth; 6. Orbital velocity of 3,080 m/sec; 7. Orbiting object; 8. Common angular velocity of the Earth's rotation and of the orbital motion.
Furthermore, if we adjust the orbit in such a fashion that it is now exactly in the plane of the equator, then the object would continually remain over one and the same point on the equator, precisely 35,900 km above the Earth's surface, when taking into account the radius of the Earth of around 6,400 km (Figure 54). The object would then so to speak form the pinnacle of a enormously high tower that would not even exist but whose bearing capacity would be replaced by the effect of centrifugal force (Figure 55).
Figure 55. An object orbiting the Earth as in Figure 54 behaves as if it would form the pinnacle of a enormously giant tower (naturally, only imaginary) 35,900,000 meters high.
Key: 1. Earth's axis; 2. Earth's rotation; 3. Free orbit; 4. Equator; 5. Imaginary giant tower 35,900,000 meters high; 6. Freely orbiting object, like a pinnacle of a tower, remaining fixed over the Earth's surface.
This suspended "pinnacle of the tower" could now be built to any size and equipped appropriately. An edifice of this type would belong firmly to the Earth and even continually remain in a constant position relative to the Earth, and located far above the atmosphere in empty space: a space station at an "altitude of 35,900,000 meters above see level." If this "space station" had been established in the meridian of Berlin, for example, it could continually be seen from Berlin at that position in the sky where the sun is located at noon in the middle of October.
If, instead of over the equator, the space station were to be positioned over another point on the Earth, we could not maintain it in a constant position in relation to the Earth's surface, because it would be necessary in this case to impart to the plane of its orbit an appropriate angle of inclination with respect to the plane of the equator, and, depending on the magnitude of this angle of inclination, this would cause the space station to oscillate more or less deeply during the course of the day from the zenith toward the horizon. This disadvantage could, however, be compensated for in part when not only one but many space stations were built for a given location; with an appropriate selection of the orbital inclination, it would then be possible to ensure that always one of the space stations is located near the zenith of the location in question. Finally, the special case would be possible in which the orbit is adjusted in such a manner that its plane remains either vertical to the plane of the Earth's orbit, as suggested by Oberth, or to that of the equator.
In the same manner, the size (diameter) of the orbit could naturally be selected differently from the present case of a stationary orbit: for example, if the orbit for reasons of energy efficiency is to be established at a greater distance from the Earth (transportation station, see the following) or closer to it, and/or if continually changing the orientation of the space station in relation to the Earth's surface would be especially desired (if necessary, for a space mirror, mapping, etc, see the following).
What would life be like in a space station, what objectives could the station serve and consequently how would it have to be furnished and equipped? The special physical conditions existing in outer space, weightlessness and vacuum, are critical for these questions.