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is neither stressed nor deformed. All this would strictly be true only if the body were homogeneous in density and elasticity. How- ever, the human body is not even approximately homogeneous, and the various parts of the organism are differently affected by the acceleration of gravity. Nevertheless, the individuals who parti- cipated in weightless experiments were impressed by the similarity between the sensation of weightlessness in flight and that of sus- pension in water. Null-Gravity Simulator 1. Null-gravity simulation was obtained by immersing sub- jects in water. The experiment was conducted at the U. S. Air Force School of Aviation Medicine, Randolph Air Force Base, in September 1956. 2. For the experiment the swimming pool was used, and a tilt-table was placed at a depth of about seven feet on the bottom of the pool. A large protractor, calibrated in degrees, measured the angle of tilt. The subject was blindfolded, and respiration was secured by means of a portable high-pressure air-lung device with a regulator and a mouthpiece. The subject was attached to the tilt- table by an aircraft safety belt. 3. The table was hand-moved slowly by an observer through varying angles of tilt. Starting positions varying from 0° to 90° with the vertical were used in a random fashion. 4. The theoretical basis and equations representing the phy- sical conditions for the subject were given above. An attempt was made to keep any change of acceleration at a value less than the threshold of stimulation of the semi-circular canal. 5. The subject was required to signal the instant he was certain that his position had changed from the original position and to indicate the direction of change. In general, major changes in the position of the tilt-table were necessary before they were identified by the subject. 6. The modest experimental setup, using hastily assembled equipment, was not sufficient to provide accurate quantitative results. However, an average of about 17° was necessary to detect positional changes. In almost every experiment the clues to change of position were factors unrelated to vestibular stimulation, but rather to the crudeness of the setup--factors such as change in pressure within the middle ear and sinuses, bubbles passing over 108
the skin, change of water temperature, or rough movement of the tilt-table. Moreover, it was noted that beginning from a vertical head-down position (180°) very large movements of the table (of the order of 100°) did occasionally take place before their direction could be identified. 7. The technical problems which were encountered could not be solved satisfactorily. Although the subject could get to the surface immediately after loosening the safety belt, the three main participants developed bilateral, acute, otitis externa, thus termi- nating prematurely the experiment. 8. Cost of the devices used and expenses for the experiment were very low due to the availability of the equipment at Randolph AFB. 9. The study was terminated with the transfer of Major L. A. Knight, USAF, (MC), in 1957. 10. References included in the general bibliography at the end of this report. Supplement 1. In the spring of 1957, Captain Grover J. D. Schock, Assistant Chief, Biology Branch, Aeromedical Field Laboratory, AFMDC, Holloman AFB, conducted a series of similar experiments in the El Paso YMCA's indoor pool. The subjects were placed on a tilt- ing seat in eight feet of water and blindfolded (see Figure 66). Later in the same year, underwater experiments were made in the pool of the New Mexico School for the Visually Handicapped in Alamo- gordo, N. M. These tests demonstrated an impairment of orienta- tion somewhat like that found in aircraft experiments without visual clues. In one type of underwater experiment, subjects were tilted as much as 22° before perceiving the tilt. Similar studies were performed by R. M. Margaria of the Laboratory of Physiology, University of Milan, Italy. Position orientation was investigated by attaching a watchlike indicator to the body of the subject. A pointer rotating about the center of the indicator was used by the subject to indicate the subjective vertical. The direction of the gravitational vertical was given by an air bubble released from time to time in front of the indicator. The error made by the subject was recorded. His respiration was maintained through an automatic underwater oxygen-breathing 109
(Official USAF Photo) Figure 66. Experiments on the Effect of Simulated Weightlessness Through Water Immersion apparatus which was carried by an experimenter to prevent any possible pull of the subject's body, while an assistant was in charge of placing the subject in different positions and of recording the data (see Figure 67). (Journ. of Aviat. Med. 29: Figure 67. Experimental Setup for Orientational Experiments Under Water 110
The results of these experiments were very interesting. The subject seemed to be completely disoriented at first, the vertical was estimated at random, and errors up to 180° occurred; i. e. , the subject often indicated the direction opposite to that requested. Only after four or five tests did the subject achieve more reliable results. In positions close to normal, and after a period of train- ing, an average deviation of about 12° from the true vertical direc- tion was obtained. NASA Weightlessness Simulator 1. Work with the NASA weightlessness simulator was conducted at NASA-Langley Research Center, Hampton, Virginia. Size of the present staff unknown. 2. The simulator which consists primarily of a water-filled tank is driven by an air motor at various rates of rotation up to two cycles per second. The air supply for the subject is located in the water tank and the air exhaust is to atmosphere (See Figures 68 and 69). EIEICENC* DUMP HUTCH (EACN EDI) ⢠- ' ⢠I . !'-<-⢠. j_ (NASA Langley Res. Cen.. Hampton. Va.) Figure 68. NASA Weightlessness Simulator 3. The subject can be oriented in the tank as shown in Figure 69 and also can be turned 90° so that the axis of rotation would pass through his shoulders. The vertical location of the subject is arbitrary and can be changed so that the axis of rota- tion passes through any level between the subject's buttocks and his ears. (See Figure 70). 1ll
Figure 69. Photograph showing external configuration of NASA weightlessness simulator with access platform in position. 4. See above. 5. A communication system is provided so that the subject can communicate directly with the operators. No information available at present about the type of loop system used and about the types of recording facilities. 6. The rate and depth of the subject's respiration will be continuously monitored. In some of the tests, the subject will be required to perform simple tasks. Electrocardiographs and skin resistance are among the measurements to be made in some of the first experiments with a human subject, as well as the breathing rate and depth. 112
Figure 70. 7. Provision has been made so that either the subject or the operators can dump the water in case of emergency. Time to empty is estimated to vary from four to fifteen seconds depending on test conditions. Air valves have been provided to prevent cavi- tation when dumping. 8. The approximate cost of the use of the simulator is esti- mated at about $160 per hour. Arrangements for use should be made through NASA headquarters. The prospective subject should have some previous training in underwater diving with self- contained breathing equipment. No experiments are scheduled at the present time. 113
Messrs. Ralph W. Stone, Jr. , and William Letko will be in charge of the use of the simulator. Mr. Stone is a Research Engineer and Assistant to the Chief of the Stability Research Divi- sion. Mr. Letko is a Research Engineer from the Missile Systems Section of the Stability Research Division. 9. Preliminary tests of the tank not involving humans or animals were scheduled for July 1959. Tests with a human subject were made in 1959-60. They were discontinued in 1960-61. 10. NASA-Langley Research Center, Langley Air Force Base, Hampton, Virginia. WADC Frictionless Device 1. One of the aspects of human performance in the weightless state is lack of friction. In order to study this problem, some devices have been developed by the Unusual Environment Section of the Engineering Psychology Branch of the Aeromedicine Lab- oratory, Wright Air Development Command. Size of the present staff unknown. 2. Devices used to operate frictionless are, in general, metal discs supported above a smooth surface by air introduced under pressure between the discs and the surface. The first such device employed at the WADC is the rotary platform constructed by D. A. Huber. It consists of a circular plate 36" in diameter, pivoted in the center and supported by pressurized air. By virtue of its center pivot, it has only one degree of freedom, that of rotation. In an attempt to obtain complete freedom in the horizontal plane, another device was developed in which compressed air is delivered through a center hole from the top of a circular plate rather than through the surface under the plate. This allows the circular plate to float freely over the surface, thus giving it three degrees of freedom--two for translation in the horizontal plane, and one for rotation about a vertical axis. This development was carried out by D. A. Huber and M. J. Warrick, also of the WADC. In another design, three of these plates are mounted under a tubular framework to produce a tricycle-like device capable of carrying a man (see Figure 71). This model was constructed by J. F. Rievley, WADC, based in part on information provided by the Ford Instrument Company. Further improvements included a triangular platform mounted on three of the plates and a square platform mounted on four of the plates. These platforms were developed to handle equiprrient and carry loads in excess of 400 lbs. without "grounding" or sticking. 114
(Official USAF Photo) Figure 71. WADC Frictionless Device 3. The motion of the device is in accordance with the law of conservation of momentum; i. e. , mlv1 = m2v2, for the linear case where ml and m2 are the masses, and v1 and v2, the velocities of the bodies involved. For the case of rotation, the law is that of conservation of angular momentum, and is expressed by llw1 = l2w2. where l1 and \% are the moments of inertia, and w1 and W2 are the angular velocities. From this it follows that a most diffi- cult situation occurs, if a man is performing a bodily task in a frictionless state. Any force applied by the man will, by its re- action, move him away from the equipment. This is in accordance with Newton's third law, while the magnitude of the man's motion is described by Newton's second law. The experimental situation is an unstable one. If a man wants to work, he will have to attach himself to the equipment. Thus, the situation changes immediately to the converse of the case with the man attached and free equipment; i. e. , the man himself will tend to rotate about his point of attachment when he applies a force to the equipment. His rotation, as that of the equipment before, will depend upon his moment of inertia in this position, and the torque he applies. 4. As mentioned earlier a direct consequence of the zero-G condition is loss of the friction normally occurring as a result of 115
gravity. This follows from the definition of a frictional force. This is the force which must be overcome in order to start a supported mass in motion or to keep it in motion at a constant velocity. The former is called the static frictional force; the latter the sliding frictional force. The frictional force in either case is a certain fraction of the force normal to the plane on which the mass rests or moves. Expressed mathematically, f= \L F, (60) where f is the frictional force, F the normal force, and ^ the co- efficient of friction, the constant of proportionality relating these two forces. The value of ji is different for the static and sliding conditions, being generally greater in the static case. From the equation, it follows that when there is no normal force, as in the weightless state, there is no frictional force; i. e. , when F = 0, f = 0, too. Frictionlessness, then, accompanies weightlessness; and a device or situation in which friction is effectively eliminated can be used to simulate one important aspect of weightlessness. In early experiments, a six-inch piece of 7/8-inch hexagonal steel stock material was used as a handle for the subject. The material was oriented with its longitudinal axis placed horizontally, and one end fastened in a torque-meter. The subject stood normally and grasped the handle which was at about waist level. The subject was instructed to apply and maintain torques by twisting the handle clockwise and counterclockwise, respectively, and their magnitudes were read directly on a torque-meter. In another experiment, the rotation of a man by reaction to a torque was investigated. Figure 72 shows the rotary frictional platform with a subject about to exert a torque on the overhead handle. The experiment at the left was set up to time a single revolution, and thus determine the rotation rate caused by the reaction to the torque. The measurement was accomplished auto- matically by use of a microswitch actuated by the platform. Re- action force to a torque applied to handhold by a subject on the frictional scooter was measured by a strain-gauge device at his right hand. 6. A continuous record of the subject's applied force was ob- tained on an ink oscillograph receiving the output of the bridge amplifier used with a strain-gauge. 7. No data available. 116
(Official USAF Photo) Figure 72. Torque Tests on the WADC Frictionless Platform 8. Cost of device and of its use by others unknown. Request for the use of frictional device by other agencies should be directed to: Commander, Aerospace Medicine Laboratory, Wright Air Development Center, Wright-Patterson Air Force Base, Dayton, Ohio. 9. Future tests involve the development of a six-degree of freedom mechanical, frictional device, the investigation of mass- force relationships in the frictionless condition, and the develop- ment of tools and equipment adequate for work under weightless conditions. Moreover, a twin gyro backpack will be developed for the stabilization of man in the zero-G condition. 10. References included in the general bibliography at the end of this report. Orbital Air Bearing Simulator, Space Task Group, Langley, Virginia National Aeronautics and Space Administration The simulator is a device being constructed for training of pilots for Project Mercury. It consists of a couch, such as those 117
to be used to increase the pilot's G tolerance in Project Mercury, mounted on top of a five inch diameter ball. This ball is in turn supported in a hemispherical cup but rides on a cushion of pres- surized air rather than a metallic contact. The subject lies on his back on the couch which is inside a mock-up of the Mercury capsule. He has a side-arm controller which can give the simu- lated capsule angular motions but not translational motion. The capsule can rotate up to ±45° in pitch or roll with unlimited rota- tion in yaw (p, q, r). The over-all weight of the apparatus from ball up is approximately 1,000 pounds. No damping is provided; however, the device does closely simulate the torque-to-inertia ratio of the full scale vehicle. The rotational cues to the pilot should therefore be realistic. The pilot will be provided with instruments and will have the periscope-type display system to be utilized in the flight vehicle. Through his periscope he will see on a screen a back-projected view of the earth scaled to correspond to his expected flight altitude. With this device, he will be able to realistically simulate his control problems for manual flight while in orbit, except for those brief times when longitudinal accleration (x) is dominant. A picture of the simulator is shown in Figure 73. The Multi-Axis Test Facility 1. The Multi-Axis Test Facility was constructed during 1959-60. It is located at the Lewis Research Center, NASA, in Cleveland, Ohio. The present staff consists of about 25 pro- fessionals and technicians. 2. The device, shown in Figure 74, consists of three con- centric supporting structures that have been fabricated from thin- wall aluminum tubing two and one-half inches in diameter. Each of the cages is gimbal-mounted to permit rotation through 360° at rates up to 360°/sec. The entire system is mounted in a yoke, 21 feet in diameter, in the Lewis Research Center's Altitude Wind Tunnel. A 50 foot diameter section of the Tunnel has been con- verted to accommodate the facility. The Wind Tunnel is capable of operating at a pressure equivalent to an altitude of 100,000 feet. Payloads up to about 2, 000 lbs. of thrust can be tested. 3. Pitch, roll, and yaw maneuvers are possible, either independently or in combination, to simulate random tumbling. Propulsion of the two outer cages is produced by a jet-reaction system, wherein gaseous nitrogen contained in spherical tanks at 118
Figure 73. Orbital Air Bearing Simulator 2,200 psi is expelled through small nozzles located on the periphery of each cage. Further, the innermost cage has installed on it ten reaction motors, eight of 20 lbs. thrust each and two of 5 lb. thrust. A total of 5 lbs. of thrust is provided in the innermost cage in the roll direction and 40 lbs. in each of the yaw and pitch modes. Rotation can be initiated from the ground control station as well as from the subject's position within the facility. 4. The objective of the facility is to test the behavior of payloads during tumbling motion. This also includes the reactions and control capabilities of a human subject in a state of frictionless motion depending primarily on the inertia of the moving mass. The 119
assumption that the pilot of a space vehicle will counter each com- ponent of a multi-axis rotation individually leads to the conclusion that the energy required to counter multi-axis rotation would be the sum of the energies required to counter each single axis com- ponent. However, the fixed position of the jets used to counter the rotation of the multi-axis test facility makes this untrue. The pilot cannot react fast enough and with sufficient accuracy to apply counter thrust at high rates of rotation. The instruments he uses usually move too rapidly from a full scale position in one direction to that in the other so that he is unable to follow. Moreover, during rotation of 30 rpm or higher about all three axes, a feeling of dis- comfort was experienced, which took the usual forms of motion sickness after a prolonged exposure to continuous spins. Figure 74. The Multi-Axis Test Facility installed in the altitude wind tunnel. A pilot is shown in the support couch. 120
5. The test subject is seated at the center of the innermost cage in a specially molded Styrofoam couch to reduce body shifting during maneuvering. He is restrained by means of leg and thigh straps and a chest support harness. The subject's head is held in place by a Lombard flight helmet that is maintained in a fixed position. The upper part of the subject's body is enclosed in a light-proof compartment to eliminate visual orientation during the tests. Only the subject's arms are free to move. The axes of rotation converge near the chest of the subject. Communication is maintained between the pilot and the ground control station by radio. Orientation is accomplished by instruments. The on-board instrumentation display has been kept to a minimum and provides only an indication of rate and direction of rotation. The rates of pitch, roll, and yaw are indicated by individual meters. Also, a combined rate indicator (a modified LABS indicator) is provided to display the rates of rotation in a single instrument. Small panel lights are provided to indicate the direction of counter thrust ap- plied by the pilot during control operation. These are connected directly to the solenoid valves of the reaction motors and give an immediate indication of inadvertent cross-coupling, a usual and undesirable by-product of a single three-axis hand controller. The nitrogen supply and operating pressure are also displayed. The pilot's control system consists of a manually operated on-off type controller that actuates five pairs of nitrogen jet nozzles located on the innermost (roll) cage. A hand controller, capable of three degrees of motion is operated by the pilot's right hand. Movement of the hand controller to the left or right will induce a roll motion. Forward and backward motion will cause pitch, while twisting the controller will cause a yaw movement. The pilot can either start a tumbling motion or he can counter the rotation started from outside the vehicle and thus stabilize the attitude of the vehicle. 6. Three rate gyros are used to measure the rates of rota- tion about the orthogonal axes. The gyros are mounted beneath the pilot's seat such that they are perpendicular to each other. They operate about the longitudinal, vertical and horizontal axes as viewed from the pilot's position; that is, the vertical axis is defined to pass through the length of the pilot's body. Rotation about this axis is termed yaw motion. When the pilot is seated upright, this maneuver coincides with the familiar use of yaw as it occurs in an airplane. If the pilot is turned 90° about the hori- zontal axis, either on his back or face downwards, lateral movement 121
to his left or right is still yaw motion. Similarly, roll is defined as rotation about the axis passing through the pilot's body from front to back; and pitch is motion about the axis passing from the pilot's left to right side. In addition to the gyroscopic instrumentation, each cage is equipped with a potentiometer that indicates the relative position of the cage with respect to the other two cages. Both the position and rate indications are recorded on a high-speed oscillograph outside the test vehicle. In addition, the duration of activation of each set of jet nozzles is also recorded. 7. Motion can be stopped by means of an automatic brake, which can be initiated by the subject or by the controller on the ground. 8. Inquiries about use by other agencies than NASA, and cost estimates, should be made to the Director, Lewis Research Center, NASA, Cleveland, Ohio. 9. Projects are active on the study of physiological conditions during spinning and tumbling. One study on ocular nystagmus by personnel of the Lewis Research Center has been concluded. 10. (1) Pilot Control of Space Vehicle Tumbling, and (2) Pilot Reaction to High Speed Rotation; both by James W. Useller and Joseph S. Algranti, Lewis Research Center, NASA, Cleveland, Ohio. Martin Reaction Control Simulator 1. The construction of a Reaction Control Simulator has been proposed by the Space Medicine Section of the Martin Company, Denver, Colorado. A similar device, based on the principle of frictionlessness by means of air bearings, is now under construc- tion at the Ames Research Center, NASA, Moffett Field, Cali- fornia. The size of the present staff is unknown. 2. The Martin simulator is a spherical shell 10 feet in diameter (see Figure 75). The shell will be made from two hemi- spheres of fiber glass construction. The sphere is supported on a contoured base from which a stream of air forms an air bearing be- tween the base and the sphere, reducing friction to a minimum during rotation. The supporting air will be directed from a nozzle in such a way as to suspend the sphere above the base, with no connection between. It will require approximately 6 psi to support 122
Figure 75. Martin Reaction Control Simulator General Arrangement of Basic Unit this sphere. The 84 inch diameter base is supposed to have a spherical seat to support the simulator when it is not supported by the air stream. The seat of the base will match the radius of the sphere with the exception of a small area around the air nozzle. It will be covered with a resilient material to protect the sphere's smooth surface. The gross weight of the sphere, including a 230 lb. man and the basic instrumentation, will be approximately 1,500 lbs. The center of gravity of this sphere will be its geometric center, and the installation of instruments and other hardware is arranged to achieve this balance. Within the sphere, a honeycomb floor, structurally supported by extruded aluminum members, is 123
installed on either side of the seat and serves as a convenient land- ing for servicing the simulator and for access to the pilot's seat. The area under the floor can be utilized for the location of equip- ment. 3. The simulator described in the Martin proposal has the following dynamic characteristics: (a) The sphere, supported by the air cushion, is capable of rotating about any of the three axes in the same manner as a space vehicle. Reaction jets at the surface can be used to orient the sphere in any direc- tion. These thrust jets simulate the hydrogen peroxide jets applied in manned space vehicles. (b) The mass and moment of inertia is compatible with cur- rent space vehicle designs and these factors can be varied over a wide range to give a more exact simula- tion of specific designs. (c) The reaction jets are energized by an on-board air supply which the pilot must learn to conserve as he would in an actual space vehicle situation. 4. The device is based on the air bearing principle, as described before. The advantage of this system is complete free- dom of rotation around the center of gravity. 5. A pneumatic reaction jet system, consisting of 12 fixed air jets, will be located on the periphery of the sphere. A set of four jets is located at each pole of the sphere, while four single jets are located on the equator of the sphere. With the sphere supported by the air bearing, it has unlimited rotation in any plane by means of the control stick mounted to the arm of the pilot's seat. This is an unrestrained movement control stick designed for finger- tip operation; i. e. , full range of movement of the stick will be ac- complished by use of the fingers only without movement of the wrist or arm. The reaction jets impart movement to the sphere in any of the three principle axes. The control stick is spring- restrained to hold it in a central position when no finger pressure is applied. The stick is twisted to achieve a pure yaw; moved to the right or left for a roll; and forward or backward to achieve pitch motion. 6. The simulator is capable of being instrumented for the more sophisticated program of space flight training such as inertial 124
guidance, radar displays, celestial navigation, terminal landing control, etc. The control system is capable of accepting a pro- grammed flight through an on-board tape recorder and signal- mixing circuit. Any degree of complexity in the programming is feasible. Flight attitude indicators and communications systems are available. 7. For operational safety, revolutions are limited to a rate where the stored energy due to rotation of the sphere is less than the work required to roll the sphere over the edge of the base. Maximum revolution rate is therefore established by calculation at 20 rpm. Malfunction of the air supply will cause the bearing to collapse and stop the sphere. The pilot may then be stopped in any position. In this case, the sphere can be relocated to re- lease the pilot. The doors are equipped with flush mounted latches and may be opened from inside or outside. 8. Approximate construction costs are unknown. Informa- tion about the use of the NASA Air Bearing Reaction Control device by other agencies may be obtained from the Director, Ames Re- search Center, Moffett Field, California. 9. No information is available at the present time on projects planned for the NASA device. 10. The description of the Reaction Control Simulator is based on the Martin Report M-M-P-58-51, which contains pro- prietary information of the Martin Company not to be utilized by any other agencies without permission. The Martin Reaction Con- trol Simulator has been described in the company report as of November 1958. It is assumed by the author that the air bearing reaction control device constructed at Ames is based on the same main principles. 125
