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Utilizing Man's Vision in Space The justification of placing man in space has in the recent past evoked much heated discussion. The final decision to put him there has been made, however, so the question is now mainly one of academic interest. A second question which is pertinent and requires much serious consideration is: To what use shall man be put so as to "earn hie keep"? As Westbrook (1959) says, "Man has certain physical limitations which are a drawback in certain cases. He has a slow response in comparison to certain servo systems. His attention wanders and he makes mistakes. He needs rest, relaxation, and refreshment. On the positive side, we can mention his wide versatility as a sensing system, his computing and judgment ability, and his adaptive optimalizing servo characteristics. Finally, we could mention the regenerative or self-repairing characteristics of man in which, after rest and food, the body and mind are fitted again for another period." Some of the possible situations are now examined in which man's vision may be found useful, in addition to those tasks associated with maintenance and the routine monitoring of instruments. "Launch "One of the few functions to which a human operator might . . .contribute during launch is the achievement[, monitoring,] and maintenance of proper vehicle attitude. . . .During this phase of flight, observation and reconnaissance functions outside of the vehicle may be dismissed as of negligible importance. It will be necessary to maintain proper [pitch,] roll, and yaw angles, and to follow a prescribed flight path. 29
Outside vision may afford reference for some of these functions in the form of the horizon or stars. However, particularly at night, booster flare may reduce visual capability. Instruments, [however,] will afford a more complete and precise reference. . . . Although external vision may provide a primary reference in the initial stages of a horizontal launch, it probably should be con- sidered of importance only as secondary or* as a backup reference during launch in most other circumstances. Some external cues, such as steam clouds from correctly functioning reaction nozzles, may afford indications of proper vehicle function during launch as well as during other phases of flight. The checking of these indications, however, should not involve unique or difficult visual perception tasks." "Orbit "The human eye can be assumed to possess a resolution capability of between one and ten minutes of arc for a wide range of illumination conditions. The recognition of a pattern which includes a number of identifiable char- acteristics may be assumed possible if distinguishing elements of the pattern subtend visual angles of ten minutes or arc or more at the eye of the observer [and the illumination and contrast conditions are satisfactory]. The required length of an object in feet to meet this criterion is equal to fifteen times the distance of the observer in miles. At an altitude of 100 miles the horizontal linear dimensions of recognizable objects or patterned elements should therefore be of the order of 1,500 feet. Geographical features will meet this criterion for direct vision. Many man-made objects will not. When a periscope which pro- vides magnification is available many more objects on the earth's surface will become resolvable, but the duration of time the object is within the field of the periscope will be substantially reduced if the periscope is fixed in relation to the vehicle and does not track a ground point. It has been estimated that, under certain conditions, an object imbedded in a pattern should be exposed for twelve seconds in a stationary display to maximize the probability of its detection (Boynton, Elsworth, fe Palmer, 1958). Magni- fication of small objects (20 to 30 feet in length) to the point where they become resolvable may reduce the time they are visible to one or two seconds, or even a fraction of a second and in addition they will be part of a pattern which is moving rapidly over the visual field. Increases in magnification will. . .[have the additional effect of 30
increasing angular velocity. Several studies have shown that visual acuity under such conditions will] be affected at rates as low as 30-40 degrees per second (Ludvigh & Miller, 1958; Miller, 1958). Swartz, Obermayer, & Muckler (1959) have analyzed the problems of reconnaissance in considerable detail for orbital vehicles at altitudes from 100 miles to over 22,000 miles. [These authors state that "the effectiveness of even the best man-optical system in performing reconnaissance is certainly questionable. Thus, feasibility of including an optical system in an orbital vehicle is certainly diminished."] It may be concluded[, therefore,] that the visual observation of man-made objects, unless these are fairly large (e.g. , cities, highways, rail- roads) will not be a practical possibility from an orbiting satellite." "Orbital Rendezvous "[As suggested previously] a problem of considerable importance within the very near future will be that of reaching an orbital vehicle with another vehicle launched at a later time. The creation of an orbiting space station of any appreciable size will probably require a step by step construction procedure in which part at a time is placed in orbit. The problem will be to place those parts which are launched subsequent to the first not only in the same orbit, but at the same point in that orbit. The accuracy required with respect to trajectory and burnout velocity to accomplish this within miles affords a tremendous challenge. Terminal rendezvous will require a system within the rendezvousing vehicle which can assess the error which exists between its orbit and position and those of its target. The system then must afford controlled application of thrust which will correct the error in order to achieve the terminal rendezvous." For example, assuming that two vehicles are traveling in the same orbit about the earth but at some distance apart, if one speeds up to catch the other he will find himself going too fast for that orbit and thus will rise to a higher one. In a higher orbit he must go at a lower speed, however, and so instead of gaining he falls farther behind. Now, if he slows down further, he will fall to a lower orbit where he will go at a higher speed. If the orbit is low enough he will 31
catch up, but will be too low and going too fast, so that he will soon pass the other vehicle. Now, however, if he speeds up properly he will rise to the original orbit and thus slow down, and if lucky will reach the other vehicle. If he is not lucky the process will have to be repeated. It is clear that achieving a rendezvous in space, either with another vehicle or with a space platform, is indeed a difficult proposition. As DuBridge (1960) points out in a recent book, one should be skeptical when discussing the use of stationary platforms "anchored in apace." The nearest approach to a stationary platform rotating about the earth would be one in a 26,000-mile orbit, with a 24-hour period equal to the earth's rotational speed. Such an object will appear to be stationary only if the orbit is exactly circular, at the right height, and exactly in the plane of the earth's equator. Even so, according to DuBridge, "it is traveling at 6,800 miles per hour, and is not something you can easily hop on and off of like a alow streetcar." "It is quite possible that a man, employing direct vision, may be included in such a system" as suggested earlier in the discussion of motion perception. Although some of the visual problems en- countered here are similar to those in formation flying and aircraft rendezvous, the lack of an earth reference and the velocity problems just mentioned make any judgments more critical. If a human can be employed in the final stages of rendezvous it might simplify certain aspects of the navigational system due to the fact that the required 32
tolerances would be eased. "It would seem desirable to study this problem in the laboratory in a simulated setting," particularly with respect to advance training of astronauts for such missions. [Detection of Other Vehicles in Space] "External visual observations for the purpose of detecting other space vehicles or objects in space may be considered of negligible importance except in situations where contact with such vehicles or objects has been specifically planned. Relative velocity between two objects increases rapidly as their orbits deviate and the amount of time in which an ob- ject the size of a space vehicle (e.g. , 50 to 100 feet in diameter) would be visible decreases commensurately. Vehicles will not be placed in orbit to search for other vehicles that are not already known to be in a specific orbit, and vehicles already in orbit may expect to be approached by other vehicles in a restricted manner. The approaching vehicles will be assuming essentially the same orbit as the target, probably even when their mission is hostile. The accuracy requirements considered in conjunction with time available for correction in almost any other case will be beyond practical limits for some time to come." [Astronomical Observations] "Visual observation of stars from an orbiting vehicle may be of considerable importance for the purpose of fixing position. Visual astronomical observations will probably not be of scientific importance, however. Although an orbiting vehicle may be above the earth's atmosphere and hence will be exposed to approximately 30 per cent more visible light in addition to which observations will not be subject to atmospheric shimmer, there are other factors which will minimize the importance of astronomical ob- servations. In the first place, considerable attenuation of the available energy will be necessary to afford pro- tection of the man from ultraviolet [ and infrared] radiation [as mentioned in a previous section]. The nature of ma- terials required in any system which permits vieion outBide of a space vehicle will be dictated to some extent by the requirement that the vehicle's structural integrity be main- tained. This will also result in the attenuation of available visible energy. In addition to required attenuation of energy, it will not be possible to include telescopes which begin to approach the size of terrestrial installations in orbiting 33
vehicles. Finally, the maintenance of stability in a manned orbital vehicle of moderate size will pose a serious problem for astronomical observations of precision." "Lunar and Interplanetary Flights "During the major portion of an earth-lunar, or inter- planetary flight, there will be no available horizon or ground plane to provide a reference for visual observations. External visual observations of the stars and planets may be of importance to check position and course as a check on the stellar guidance system which may be used. ..." The brief orbital flights and ballistic shots achieved thus far indicate that man does not lose his intellectual abilities, and that he can control and interpret displays under space flight conditions. It is not unreasonable, therefore, to suppose that he could perform cer- tain navigational tasks based upon a mixture of direct sensory data and instrumental data. "Such observations will require training in the recognition of celestial patterns and in the nature of changes in patterns with respect to positions of planets which will occur on a specific flight. Such training may be accomplished in a specially designed planetarium which can simulate an appropriately moving point of observation." "Landing "The nature of external visual tasks which may be re- quired of a pilot during landing will vary with the conditions under which the landing is made. In many circumstances landing will be initiated from orbital flight around the target by firing a rocket which is oriented to reduce orbital velocity. This will result in a vehicle falling in toward the surface of the target. The timing of firing of a retrograde rocket must be carefully controlled in order to land in the desired area. Such timing is best controlled from the ground where pre- cise fixes of orbital vehicle position can be made. Ground support will not always be available, however, and vehicle position may be marked visually by observation of transit of some recognizable landmark on the surface. The deviation 34
of surface position. . .by five miles for each second of error in firing of a retrorocket is not extreme so that timing of firing by a man in the vehicle might be within necessary limits of accuracy. Landing from orbit about a relatively unknown planet or moon will be far more difficult than landing on the surface of the earth. It will be difficult to select appropriate landmarks when the character of the surface is relatively unknown and the relative position of available landmarks with respect to a desirable launching site are not known. [Whenever possible such landings will be controlled by automatic sensing devices.] Several reconnaissance orbits may [ , however,] afford visual information upon which some decision can be made. For purposes of communication the earth-side of a distant body may be preferred. The relative difficulty of final selection of a desired landing site will be reduced with reductions. . .[in ground speed]. The extent to which it may be reduced or eliminated will depend upon the nature of the landing. "If the target has an atmosphere, such as the earth, the atmosphere will be utilized for deceleration of the vehicle prior to landing. Landing may be accomplished by aerodynamic control as in the case of conventional aircraft and the X15 research vehicle. In this case it will be necessary for the pilot to maintain continuous control. Limits of dynamic pressure, acceleration, and heating must not be exceeded and it seems probable that the human pilot can function in this kind of situation. During the early stages of re-entry into an atmosphere, instruments will probably provide the best source of information for the control task. In the final stages when speed has been reduced and actual landing is about to be made, external visibility of the surface upon which the landing is to be accomplished and the surrounding terrain can be expected to be important for selection of the final location or for alterations in the point of touchdown. "In addition to pilot-controlled aerodynamic landings, aerodynamic landings which involve a high-drag capsule must be considered. In this case, less control can be effected by the occupant of such a vehicle. Some control will be possible, however, by alteration of capsule attitude or by the use of reaction nozzles for modest alterations of flight path. It is unlikely that external vision will provide a reference here, but it is at least a possibility in the final stages. In the last stage of such a landing a parachute probably will be deployed. This will be controlled 35
automatically. If the automatic system should fail the pilot may effect parachute release when an appropriate altitude and speed have been achieved. It is doubtful that the point of release will be determined by external visual reference except as an emergency backup. This will be difficult over water and other areas with relatively homogeneous surfaces. "In the absence of a suitable combination of atmosphere, gravitational field, and vehicle design, landing will have to be effected by the application of a reaction thrust to slow the vehicle. When such a landing is made from orbit, it will involve initial retrofiring to drop out of orbit, followed by the continued application of retrograde thrust to'reduce both vertical and horizontal components of velocity with respect to the surface of the target. The horizontal velocity may be reduced to zero in a variety of ways somewhat arbi- trarily. The vertical velocity, however, must be so con- trolled for a. . .given acceleration field that it will juet be reduced to a value which is sufficiently low at impact so that no damage to the vehicle or injury to the vehicle occu- pant will occur. It will be wasteful of power to reduce velocity too rapidly. The satisfactory solution of this problem will require information concerning altitude, velocity and acceleration of the vehicle during descent. It seems questionable that the efficient solution of this problem will be possible by means of direct visual refer- ence without the availability of other information. It is a possibility, however, which should be examined further. A dominating concern in selection of an optimum method of landing will concern economy of energy. In the final stage of a landing direct vision may be essential for a decision as to the adequacy of the landing site." Inasmuch aa the human eye cannot tell the nature of a surface by its reflected light, i.e., hard, soft, marshy, etc., it might prove of value to fire some test probes into the ground just prior to landing as a further aid in selecting an adequate site. It would appear then that, from the standpoint of human vision, flight into space is fraught with danger. While in a certain sense this is true, it is equally apparent that many of the dangers can be met satisfactorily. In addition, it is evident that the visual capacities of 36
man can be utilized to tremendous advantage beyond their monitoring function. If full use of the eyes is made, it may be possible to reduce considerably the tolerances required by the numerous physical subsystems. 37
