f. Visibility of Minimum Satellite Vehicle in the orbit. Another prerequisite for successful tracking is sufficient light for optical tracking instruments. The simplest method to provide sufficient illumination and contrast would be to observe the Satellite shortly before dawn or shortly after sunset. The Satellite, illuminated by sunlight, would then be visible as a fast-moving star against a relatively dark sky. A study of this possibility indicates that, in order to obtain a brightness equivalent to that of a star of first magnitude (e.g. "Capella"), the object would have to be at least 20 feet in diameter. In principle, it appears quite feasible to provide a reflecting surface of this size even within the payload limitation of 5 lb. A particularly simple solution would be a balloon, carried aloft collapsed in the fourth stage's nose, and inflated with Helium after the orbit has been attained. However, it is likely that such a balloon would soon be punctured by cosmic dust particles and become ineffective as a light reflector. Therefore, some kitelike structure may be better suited. Unfortunately, the conditions for visibility by a tracking station are severely restricted by the (unpredictable) deviations from the desired orbit caused by lack of accurate cut-off velocity control and possible cut-off tangent dispersions of the uppermost stage, as well as uncertainty of upper atmosphere density. Tracking at dusk and dawn will, therefore, be a rather haphazardous endeavor and should be supplemented by an active light source in the uppermost stage. Such possibilities have been discussed with Mr. E.P. Martz, Jr., Chief Optical Systems Section, Flight Determination Laboratory, White Sands Proving Ground. Mr. Martz has suggested to equip the Minimum Satellite Vehicle's uppermost stage with a gaseous discharge tube actuated by solar storage cells utilizing the solar radiation during the sunlit portion of flight and re-emitting as a flashing light during the night. He believes that use of solar storage batteries such as developed by Bell Telephone and by Wright Field are promising. It appears probable that such a light source, adequate for instrument tracking for a period exceeding one month, can be built within the payload limitation of 5 lb. Further studies will be required to determine whether the light flashes can be made bright enough for visibility with the naked eye. Further methods discussed to improve optical visibility of the satellite vehicle include painting of the uppermost stage with fluorescent paint (brightness could be doubled because ultraviolet light is [10] converted into visible light) and luminescent paint (will absorb sunlight during the day and omit light during the night). There is also a faint possibility for the successful use of chemical smoke trails, such as used in tracking of solid rockets. (It has to be further investigated whether this method is suited to a Satellite.) Chemical flares or shaped charges may also be feasible. Another possibility would utilize solar or artificially induced fluorescence of sodium, mercury or other metallic vapors. (The fluorescence of such vapors is greatly increased by the high ultra-violet radiation from the sun in the vacuum of outer space.) Finally, use of fluorescence of solid mediums has been discussed. (The solid mediums would be activated by small electric current and additionally by solar radiation and radioactive substances.) For ground tracking stations, normal meteor tracking cameras appear to be best suited. Such equipment is available at White Sands Proving Ground. 5. Acknowledgements. This report has been based on detail studies prepared by: Dr. William Bollay Mr. J. B. Kendrick Dr. Wernher von Braun Mr. Gerhard Heller Aerophysics Development Corporation, Pacific Palisades, California. Chief Optical Systems Section, Flight Determination Ordnance Missile Laboratories, Mr. Hans R. Palaero Redstone Arsenal, Huntsville, Alabama. Mr. Fritz K. Pauli 6. References. a. "Observing the weather from a satellite vehicle", lecture presented at the American Museum - Hayden Planetarium, May 4, 1954 by Harry Wexler, Chief, Scientific Services Division, U.S. Department of Commerce, Weather Bureau. b. "Minimum Orbital Unmanned Satellite of the Earth (MOUSE)" for Astrophysical Research. Lecture presented at the American Museum - Hayden Planetarium, May 4, 1954 by Dr. Fred S. Singer, Professor, Dept. of Physics, University of Maryland. Document II-8 Document title: "On the Utility of an Artificial Unmanned Earth Satellite: A Proposal to the National Science Foundation, Prepared by the ARS Space Flight Committee, November 24, 1954," Jet Propulsion, 25 (February 1955): 71-78. [Copyright American Rocket Society (now American Institute of Aeronautics and Astronautics), 1955. Used with permission.] In 1934, the American Interplanetary Society, one of the earliest U.S. advocates of spaceflight, had changed its name to the American Rocket Society (ARS) to improve its technical legitimacy. In 1953, the ARS invited Alan T. Waterman, director of the National Science Foundation (NSF), to attend a meeting of the society's Space Flight Committee. Soon after, the committee issued a confidential report calling for the NSF to study “the utility of an unmanned satellite vehicle to science, commerce and industry, and national defense." This report was followed in 1954 by a formal proposal, “On the Utility of an Artificial Unmanned Earth Satellite." It was partly because of advocacy groups such as the ARS that satellites were put on the government's scientific agenda. This is a proposal to the National Science Foundation that the Foundation sponsor a study of the utility of an unmanned, earth-satellite vehicle. The proposal is made by the American Rocket Society in the normal exercise of its functions.' The role of the Society in this matter is made clear by the following policy statement adopted by the Board of Directors: "The American Rocket Society should act as a 'catalyst' and should promote interest and sound public and professional thinking on the subject of space flight. It should not attempt to evaluate the merits of individual proposals or undertake work on the subject of its own accord. It should, however, encourage such activity on the part of other organizations." It is apparent, then, that the Society cannot undertake to make the study. It can, however, serve the National Science Foundation in a number of ways, and believes it is doing so in bringing this subject to the Foundation's attention. Should the Foundation elect to sponsor the study the Society could assist by encouraging scientists and engineers both inside and outside the Society to participate. The Society would be willing to perform any other service within its functions and abilities to assist the National Science Foundation in implementing this proposal. 1. The American Rocket Society is a professional engineering and scientific organization devoted to the encouragement of research and development of jet and rocket propulsion devices and their application to problems of transportation and communication. It is actively concerned with various technical aspects of space flight, and at the present time is also interested in military applications of the reaction principle. Background The proposal was prepared by a Space Flight Committee appointed by the President of the Society. The Committee decided that the study of the utility of an unmanned, earth satellite would be one of the most important steps that could be taken immediately to advance the cause of space flight, and that this step would also increase the country's scientific knowledge and, indirectly, promote its defense. Why an unmanned, earth satellite? Although many satellite proposals have been put forward, the small, unmanned satellite is the only one for which feasibility can now be shown. This opinion is held by many responsible engineers and scientists involved in rocket and guided-missile work and in upper-atmosphere research. At any rate, most of these people agree that the unmanned earth satellite would be the first step toward more ambitious undertakings. It is felt generally that, although the satellite vehicle has yet to be built, the components, i.e., power plants, airframes, stabilization systems, etc., are either available or under development in conjunction with the nation's guided-missile effort. Furthermore, the country now has nine years of experience in the techniques of instrumenting high-altitude sounding rockets, which techniques would have application to the earth satellite. Why study utility? Although many claims have been made for the utility of a satellite vehicle and many uses have been proposed, the subject has not been thoroughly investigated by a responsible organization and, at present, does not rest upon a firm foundation. On the other hand, enough is known about possible useful purposes so that most cases are readily amenable to study, and, if such a study were made, reasonably positive conclusions could be drawn. Because of recent advances in guided missiles, the cost of producing a small, unmanned satellite is probably not the mammoth sum that was at one time considered necessary. Nevertheless, the creation of even a small satellite is still a major undertaking and will require a sizable amount of money. It is important that there be justification for the expenditure of this money. The Society feels that to create a satellite merely for the purpose of saying it has been done would not justify the cost. Rather, the satellite should serve useful purposes-purposes which can command the respect of the officials who sponsor it, the scientists and engineers who produce it, and the community who pays for it. The Society feels, therefore, that the study of utility is one of the most important tasks to be accomplished prior to creation of a satellite. It was apparent to the Committee in its early deliberations that the subject of utility could not be entirely divorced from feasibility, and that some concept of feasibility would have to be assumed. This was done not to be restrictive, but to provide a frame of reference from which those considering utility could proceed. It was assumed that it would be feasible to establish a small payload in an orbit, the difficulty increasing with the size of the payload, and that means could be provided for communicating information from the satellite to the surface of the earth. With this concept in mind, various fields of utility were suggested as follows: Astronomy and Astrophysics. A satellite could overcome some of the limitations on observations made through the earth's atmosphere. cells. Biology. Of early importance would be the effects of outer space radiations on living Communication. A satellite might provide a broad-band transoceanic communication link. A future possibility is that of obtaining continental coverage when the satellite is used as a relay station for radio or television broadcasts. Geodesy (including Navigation and Mapping). The size and shape of the earth, the intensity of its gravitational field, and other geodetic constants might be determined more accurately. Practical benefits to navigation at sea and mapping over large distances would ensue. Geophysics (including Meteorology). The study of incoming radiation and its effect upon the earth's atmosphere might lead eventually to better methods of long-range weather prediction. Experiments Arising from Unusual Environment. The characteristics of the environment (weightlessness, high vacuum, temperature extremes, etc.) will suggest experiments that could not be performed elsewhere. This list is by no means complete-it is probable that the study would reveal other fields of equal or greater utility. In order to provide a preliminary sampling of opinion, the committee asked a number of scientists (chosen at random from those known to Committee members) to give brief summaries of their opinions on the utility of an unmanned, satellite vehicle. These papers are presented as appendixes to this proposal and include the following: (A) “Astronomical [72] Observation from a Satellite," by Ira S. Bowen; (B) "Biological Experimentation with an Unmanned Temporary Satellite," by Hermann J. Schaefer; (C) “The Satellite Vehicle and Physics of the Earth's Upper Atmosphere," by Homer E. Newell, Jr.; (D) “Comments Concerning Meteorological Interests in an Orbiting, Unmanned Space Vehicle," by Eugene Bollay; (E) "The Geodetic Significance of an Artificial Satellite," by John O'Keefe; (F) "Orbital Radio Relays," by John R. Pierce. Recommendation In view of the facts cited, it is proposed that the National Science Foundation sponsor a study of the utility of an artificial, unmanned earth satellite. ANDREW G. HALEY, President COMMITTEE MEMBERSHIP: Harry J. Archer; William J. Barr; B. L. Dorman; Andrew G. Haley; Kenneth H. Jacobs; Chester M. McCloskey; Keith K. McDaniel; William P. Munger; James R. Patton, Jr.; Richard W. Porter; Darrell C. Romick; Milton W. Rosen; Michael J. Samek; Howard S. Seifert; Willis Sprattling, Jr.; Kurt R. Stehling; and Ivan E. Tuhy. Appendix A Astronomical Observations from a Satellite IRA S. BOWEN Mount Wilson and Palomar Observatories The following comments are an expansion of a conversation held by H. S. Seifert with Dr. Ira S. Bowen, Director of the Mount Wilson and Palomar Observatories. The ideas herein originated with Dr. Bowen and have been reviewed by him for accuracy. Astronomical observations through the Earth's atmosphere are at present limited by three factors: (a) The resolution of detail is degraded at least tenfold by atmospheric turbulence (poor seeing). (b) Exposure time, and hence limiting star magnitude, is curtailed by fogging due to light scattered in the atmosphere. (c) Certain radiations, i.e., regions of the spectrum, are completely absorbed in the atmosphere. Thus, if optical equipment equivalent to that now available at the surface could be placed outside the atmosphere, much additional information in the form of planetary detail, new, remote, or faint objects, and short wave-length spectra would be obtained. This information would be of great interest and value to astronomers and to the sciences generally. The ideal situation would be to place the 200-in. telescope and its accessories on a firm platform such as the moon. Since optical equipment projected into an orbit on a man-made satellite will be riding on a small and relatively unsteady base, certain practical limits and difficulties will be found, as follows: Angular Resolution. The best optical resolution which the atmosphere will permit, on days of optimum seeing, which occur only a few times yearly, is of the order of 1/4 to 1/2 sec of arc. The 200-in. telescope would permit a theoretical resolving power of 0.025 sec of arc, and a 20-in. to 40-in. telescope would permit a resolving power of 0.25 to 0.125 sec of arc, if free from atmospheric effects and geometric distortions. Thus in order to make use of the transparency of space and secure more detail than can be seen from the ground, an automatic satellite orienting and guiding system would be needed which was stable to an accuracy lying between 0.10 and 0.01 sec of arc. Limiting Magnitude. Because of night sky light scattered by the atmosphere, objects fainter than a certain limiting magnitude cannot be distinguished from the general background fog. In the case of the 200-in. telescope, exposures longer than half an hour are, for this reason, not useful. In order to record objects of the same faintness, as can be done with the 200-in., a telescope of reasonable size for transport on a satellite, say 30 in., would require an exposure time of 10 to 24 hours. Since the orbital period is of the order of 1 1/4 hours, of which less than half is spent in the Earth's shadow, a mechanism would be required for shielding the telescope and camera during the sunlit periods while maintaining precise orientation. Short Wave-Length Spectra. By the use of sounding rockets equipped with sunfollowing servos, it has been possible to photograph solar spectra down to 1200 A with low resolution. The long exposures required for high-resolution solar and stellar spectra in this wave-length region cannot be obtained during the few minutes or even seconds of high-altitude flight time typical of sounding rockets. Adequately high resolution could be obtained from a spectrograph using light collected with a 12-in. mirror for detailed spectra of the brighter stars, with exposures of several hours. Since the physical dimensions of the equipment are not large and the orientation tolerances are less strict than for telescopic images, a spectrograph would probably be simpler than a telescope to get into proper working order. Telemetering of Data. If one assumes that a photographic plate cannot be recovered from a satellite, certain problems arise. Any data collected must be capable of being translated into a radio or optical signal and relayed to the ground. The photographic plate has the fundamental advantage that photons are registered simultaneously in all resolvable parts of the spectrum or image. Thus shortening required exposure time. While electronic photon counters exist which equal or excel the sensitivity of the photographic plate, they can collect energy from only one part of the spectrum or image at a time, thus increasing the required exposure time. A possible technique might be worked out in which plates are exposed and developed automatically (after the manner of the Polaroid-Land Camera), after which the fixed image could be scanned and transmitted sequentially when convenient by a photoelectronic system. Thus the stored data might be held and relayed by a transponder activated from the earth's surface only when the satellite was within radio range of a particular ground station, thus eliminating the need for a dozen or more ground telemetering stations spaced around the equator. Appendix B Biological Experimentation with an Unmanned Temporary Satellite HERMANN J. SCHAEFER U.S. Naval School of Aviation Medicine If humans are to fly in the regions at the upper end of and outside the atmosphere, an "artificial environment" has to be provided which maintains full or near sea-level values of the various physical conditions. Whereas this task can be handled, though with considerable technical expenditure, for most of the factors involved, two novel phenomena develop in vehicles moving outside the atmosphere which cannot be compensated very easily. These are the heavy components of the primary cosmic radiation and the state of weightlessness. The technical means of restoring normalcy with regard to these conditions, though theoretically available, imply prohibitive measures with regard to weight and power. The only way out is to study the effects of both influences on the human organism with the aim in mind that a tolerance can be established which does not impose too severe |