The importance of a large, permanent, manned Earth satellite was recognized quite early in the history of rocket flight. In 1929, H. Oberth1 considered many of the observational functions of such a satellite. At about the same time, a series of papers by Von Pirquet2 stressed the significance of an orbital assembly station for space-flight missions. Since that time the literature has contained numerous articles on the uses construction, and operation of space stations and specialized space vehicles. These range in quality from pure science fiction to detailed engineering computations. At least one article meriting consideration appeared in Science Wonder Stories.3 Some general descriptive material may be found in the literature.4-13
Many of the functions that could be performed by a space station could also be performed by Earth satellites which are neither large, permanent, nor manned. The unique function of the space station is its use as a base for large space vehicles. The Earth is not an entirely satisfactory base, due, in part, to the presence of the atmosphere, which presents a serious reentry problem, and, in greater part, to the strong gravitational field at the surface of the Earth.
Present rockets, and the larger ones that will become possible when development is completed on announced engines of 1.5-million-pound thrusts can send very substantial payloads onto space trajectories. However, these will still fall far short of the needs of more advanced space missions. One partial solution is to develop ever larger chemical boosters or large boosters of higher performance using nuclear propulsion. Nevertheless, the net mission capability will always be limited by the thrust of the largest booster system available at any given time. Space missions such as manned expeditions to the neighboring planets would have to await many generations of missile development. The space station offers an alternative solution.
1 Oberth Hermann, Wege zur Raumschiffart (Methods of Achieving Space Flight), 3d ed., R. Oldenbourg, Berlin, 1929.
2 Von Pirquet, Guido, die Rakete (The Rocket), Journal of the Verein für Raumschiffahrt, Breslau, 1927-29.
3 Noordung, Hermann; The Problems of Space Flying, revised English printing in Science Wonder stories, 1929.
4 The Station in Space, Journal of the American Rocket Society, vol. 63 September 1945, pp. 8-9.
5 Clark, A. C., Interplanetary Flight, Temple Press, London, 1950, especially ch. VIII.
6 Fears, F. D., Interplanetary Bases-The Moon and the Orbital Space Station, Journal of Space Flight, vol. 3, September 1951, pp. 4-5.
7 Firsoff, V. A., Artificial Satellites Explained, Flight vol. 60, October 1951, pp. 504-506.
8 Ketchum, H. B., A Preliminary Survey of the Constructional Features of Space Stations, Journal of Space Flight, vol. 4, October 1952, pp. 1-4.
9 Von Braun Offers Plan for Station in Space, Aviation Age, vol. 18, 1952, pp. 61-63.
10 Von Braun, W., The Early Steps In the Realization of the Space Station, Journal of the British Interplanetary Society, vol. 12, January 1953, pp. 23-24.
11 Ehricke, K. A., Engineering Problems of Manned Space Flight Interavia, vol. 10, July 1955, pp. 506-511.
12 Hoover, G. W., Sectional Satellites, Missiles and Rockets, vol, 2, October 1957, pp. 135-137.
13 Ehricke, K. A., Our Philosophy of Space Missions, Aero Space Engineering, vol. 17, May 1958, pp. 38-43.
This method of operation would involve several steps. Individual shipments of fuel, guidance equipment, structural material, parts, tools, personnel, and supplies would be transported from the Earth to the space station, with the size of each shipment limited by the performance of available boosters. The accumulation of components may proceed as long as necessary, and the feasible total is, therefore, essentially unlimited. Long-range spacecraft would be assembled on, and depart from the station. For certain missions the spacecraft may be returned to the station and used repeatedly. A considerable potential advantage ol the space station lies in the fact that space vehicles staged from it would have less stringent structural and propulsion requirements than rockets that must depart from and return to the Earth.
Various proposals for designing and constructing a space station have been advanced in the past.14-24 The more realistic studies show that a minimum orbital payload capability is necessary before a station may be constructed. Beyond this threshold an arbitrarily large station may be assembled. It is of current relevance to note that ICBM-type boosters with added stages appear to be about adequate for the construction of a space station. Large booster systems that can be based on 1.5-million-pound engines are certainly adequate. There is not yet sufficient information to formulate a decision as to whether or not a station should be built.
For staging of interplanetary flights, the orbit of the space station would lie in the plane of the Earth's orbit around the Sun. For long life, its altitude would be above 300 miles. To avoid dangerous radiation from the "radiation belt" it might be below 500 miles or possibly above 30,000 miles. Considerations such as these tend to limit the usefulness of the station for some secondary functions which might be performed better by less elaborate satellites, manned or unmanned.
In addition to being, a staging base for equipment, the space station would also be a transfer point for personnel. Crews intended for long space voyages could undergo a preliminary period of adaptation to the space environment aboard the station before departure. The station may a]so be used for quarantine. Returning spacecraft and personnel may possibly carry diseases or other forms of contamination, and
14 Ross, H. E. Orbital Bases, Journal of the British Interplanetary Society, vol. 8 January 1949. pp. 1-19
15 Engel, R., Earth Satellite Vehicles, Interavia, vol. 5, 1950, pp. 500-502.
16 Gatland, K. W., A. M. Kunesch, A. E. Nixon. Fabrication of the Orbital Vehicle, Journal of the British Interplanetary Society, vol. 12, November 1953, pp. 274-285
17 Dixon, A. E., K .W .Gatland, A. M. Kunesch, Fabrication of the Orbital Vehicle, In Space-Flight Problems, Laubscher & Co., Zurich, Switzerland, 1953, pp. 125-135.
18 Ehrieke, K. A., A New Supply System for Satellite Orbits, pt. 1, Jet Propulsion, vol. 24, September-October 1954, pp. 302-309.
19 Romick, D C., Preliminary Engineering Study of a Satellite Station Concept Affording Immediate Service With Simultaneous Steady Evolution and Growth, presented at 25th annual meeting of the American Rocket Society, November 14-18, 1955, preprint No. 274-55.
20 Romiek, D. C., Concept for Meteor-A Manned Earth-Satellite Terminal Evolving From Earth to Orbit Ferry Rockets, in Proceedings of the VII International Astronautical Congress, September 1956, pp. 335-380
21 Romiek, D. C., R. E. Knight, S. Black Meteor Jr., a Preliminary Design Investigation of a Minimum Sized Ferry Rocket Vehicle of the Meteor Concept, In Proceedings Of the VIII International Astronautics Congress, 1957, pp. 340-372.
22 Goodyear Proposes Smaller Space Station, Aviation Week, vol. 67, October 1957 pp. 115-119, 123.
23 Clark, E.. Convair Plans Four-Man Space Station, Aviation Week, April 1958, pp. 26-28.
24 Astronautics and Space Exploration, hearing before the Select Committee on Astronautics and Space Exploration, 85th Cong., 2d sess., on H. R. 11881, April 15 through May 12, 1958; K. A, Ehrieke, p. 632.
should not be permitted to return directly to Earth before careful observation. These functions seem characteristic of a space station used as a staging base, and may be regarded as a representative, rather than exhaustive, list.
Two outstanding problems to be overcome in establishing a space station are the problem of rendezvous between the station and supply rockets, and the propulsion requirement that individual shipments be of sufficient size to permit construction to begin. Additional problems include the details of fabrication, the provision for adequate power supply, and consideration of such factors affecting personnel as air, food, water, radiation, weightlessness, and collision with foreign particles.
The minimum practical value for individual supply loads delivered into orbit seems to be about 3,000 to 4,000 pounds. This would allow carriage of a man or men, sufficient supplies to last until resupplys communication, and guidance equipment to assist in rendezvous, and some rocket propulsion capability to alter the orbit. At least one package of tools and construction material may be placed in orbit first and the manned vehicle sent later. Although this minimum value may be theoretically adequate, it appears quite marginal with very little provision for emergencies. In particular, this weight is not likely to include provision for a safe return to earth if rendezvous fails to occur before the supplies are exhausted. On the other hand, an individual package weight of about 10,000 pounds could sustain a small crew for a considerable time and include adequate safety provisions. Something approaching an orbiting payload capability of 10,000 pounds is achievable with an ICBM booster augmented by a fairly large upper stage.25
The rendezvous problem is in a more uncertain state, although informed opinion suggests it can be solved by known techniques. Propulsion and controls must be provided to reduce position and velocity differences between the two vehicles to a sufficiently small value to permit mechanical contact by a beam or cable.
It appears, in sum, that the construction of a space station of some sort will be technologically feasible in the foreseeable future.
Bases, more or less permanent in character, will be required at some point in an expanding space program. A good deal of attention has already been given to the matter of a base on the moon.26-37 Bases of
25 See footnote 24. p. 128.
26 Comments With Respect to the Glenn L. Martin Study on Requirements for a Manned Station on the Moon, Outer Space Propulsion by Nuclear Energy, hearings before the subcommittee of the Joint Committee on Atomic Energy, Congress of the United States, 85th Cong, 2d sess., 1958.
27 Thompson G. V. E. The Lunar Base, Journal of the British Interplanetary Society, vol. 10, No. 49, March 1951.
28 Fears, F., Interplanetary Bases, Journal of Space Flight, vol. 3, September 1951.
29 Moore, P., Guide to the Moon, W. W. Norton & Co., Inc., New York, 1953.
30 Byan, C. (editor), Conquest of the Moon, Viking Press, New York, 1953.
31 Byan, C. (editor), Conquest of Mars, Viking Press, New York, 1953.
32 Von Braun, W., The Mars Project, University of Illinois Press, Urbana, 1953.
33 Clarke A. C., Exploration of the Moon, Frederick Muller, Ltd., London, 1954.
34 Sowerby, P, L., Structural Problems of the Lunar Base, Journal of the British Interplanetary Society, vol. 13, No. 36, January 1954.
35 Awdry, G. E. V., Developments of a Lunar Base, Journal of the British Interplanetary Society, vol. 13, No. 16, May 1954.
36 Shoto-Douglas, J. W. E. H., Farming on the Moon, Journal of the British Interplanetary Society, vol. 15, No. 17, January 1956.
37 Holbrook, R. D., Outline of a Study of Extraterrestrial Base Design, The RAND Corp. Research Memorandum RM-2161, April 22, 1958.
one kind or another will also be required if manned interplanetary travel is to develop in a serious way-first of all because it would be grossly inefficient to remain, say, 1 day on Mars, after taking half a year to get there; and, second, because return from a flight to, again Mars, may be really feasible only after a delay of many months the bring the Earth and Mars into favorable relative positions for the return flight.
For human beings to exist in a base on the Moon or one of the planets the internal environment must be generally the same as that in a space station. One salient difference in the two cases, however, is that the local environment of the Moon or planet must be coped with, and that local assets may be exploited. Generally speaking, the establishment and maintenance of a manned base on any extraterrestrial body would be a very difficult and ambitious undertaking. The problems associated with a base on the Moon are less difficult than they would be for bases on any other body, since the Moon is relatively close to the Earth at all times. Moreover, the average temperature of the Moon (not-withstanding the tremendous day-night variations) is not far from the average temperature of the Earth. Thus in a well-insulated base on the Moon, temperature regulation would not constitute a severe problem. If efficient conversion of solar energy is assumed and if usable local sources of water and oxygen can be obtained through chemical processing of indigenous materials, a partially self-sufficient Moon base can be envisioned.
Second in order of difficulty would come Mars as a site for a manned base. More remote than the Moon but providing a more nearly earth-like environment in many ways, Mars has a thin atmosphere which would provide protection against meteorites and some slight protection against abrupt temperature changes. Present knowledge of the surface barometric pressure is inadequate to say whether a human being outside a base would require a full-pressure suit or whether a partial-pressure Suit would be adequate. In any event, a breathable atmosphere would have to be provided, and a manned base would have to be airtight with artificial heating supplied throughout most of the daily cycle.
None of the other planetary bodies of the solar system, in the light of present knowledge, offers an attractive site for an extraterrestrial base. Venus, although often cited as a possibility, contains such high concentrations of carbon dioxide in its atmosphere and has such a dense cloud cover that establishment of a base on its surface appears orders of magnitude more difficult than in the case of Mars. More information about Venus is needed, however, before definitive statements about its suitability as a base can be made.
It has been suggested that extraterrestrial residences may be a long-term solution to the problem of accommodating the enormously increasing population of the earth. This notion, while not entirely out of the question, does exert something of a strain on credibility. However, it can probably be fairly asserted that developments for extraterrestrial bases may help by disclosing ways of dealing with unfavorable environments and thereby effectively enlarging the amount of usable land area on the earth. As a broad generalization, a vital component of large-scale control of any alien environment is access to vast quantities of power to run machinery.