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.