RESULTS OF THE THIRD U.S. MANNED ORBITAL SPACE FLIGHT, OCTOBER 3, 1962

 

1. SPACECRAFT AND LAUNCH VEHICLE PERFORMANCE

By John H. Boynton, Mercury Project Office; and Lewis R. Fisher, Mercury Project Office.

 

Summary

 

[1] The Mercury spacecraft and the Atlas launch vehicle used in the orbital flight of Astronaut Walter Schirra, Jr., performed extremely well in every respect. All objectives of the eighth Mercury-Atlas mission (MA-8) were accomplished, and no malfunctions occurred which compromised the success of the mission. The third United States manned orbital flight marked another key milestone in the Mercury program, in that the period of observation in space for both the astronaut and the spacecraft systems was twice that of previous missions. The only anomaly which caused concern during the flight was an elevated suit temperature experienced in the first 2 hours after launch. This condition was later found to have resulted from a foreign substance in the control valve, but the flight control task was further aggravated by a difference between the suit-inlet temperature readings telemetered to the ground stations and those indicated to the astronaut by the instrument panel gages. However, the elevated temperature condition was adequately remedied through effective system monitoring and methodical control valve manipulation by the astronaut. The scientific experiments included in the mission provided valuable information regarding physiographic features of the earth, the selection of filters for weather photography, nuclear radiation in terrestrial space, and the effectiveness of advanced ablation materials during an orbital reentry. The excellent performance of the man-spacecraft system during the MA-8 flight provided information and evidence which supports the immediate advancement of essentially this same system into missions of even greater duration with more ambitious objectives.

 

Introduction

 

The eighth Mercury-Atlas mission (MA-8) was planned for up to six orbital passes and was a continuation of a program to acquire new know ledge while extending the operational experience in manned orbital space flight. The objectives of the flight were to evaluate the performance of the man-spacecraft system in a six-pass orbital mission, to evaluate the effects of an extended orbital space flight on the astronaut, to obtain additional evaluation by the astronaut of the operational suitability of the spacecraft systems, to evaluate the performance of spacecraft, systems which had been modified, and to exercise and evaluate further the performance of the Mercury Worldwide Network and mission support forces in order to establish their suitability for extended manned orbital flight.

The Mercury spacecraft, Sigma 7, and the Atlas launch vehicle used by Astronaut Schirra in successfully performing the third United States manned orbital mission were nearly identical to those used for the MA-6 and MA-7 flights. The spacecraft provided a habitable environment for the astronaut. in space and protected him during the elevated heating phases of powered flight and reentry. The spacecraft also served as a laboratory in space where valuable scientific experiments were conducted. The intent of this paper is to describe briefly the significant changes incorporated into the MA-8 spacecraft and launch vehicle since the previous flight and to discuss the performance of the spaceborne systems. References 1 and 2 should be consulted for complete descriptions of the systems discussed in this paper. The spacecraft systems include those of heat, protection, mechanical and pyro-...


[2] FIGURE 1-l.-Spacecraft interior arrangement.

 

...-technic, spacecraft control, communications, instrumentation, life support, and electrical and sequential. The arrangement of these systems within the spacecraft is illustrated by a simplified schematic diagram in figure 1-1.

 

 

Heat Protection System

 

The performance of the heat protection system was satisfactory. Through the use of an ablative-type heat shield, insulation in a double-wall afterbody structure, and heatsink beryllium shingles on the cylindrical section, the Mercury spacecraft is protected against excessive heating during exit and reentry flight through the atmosphere. An alteration to the heat protection system since the previous mission was the bonding of nine ablation material samples to the exterior surface of the cylindrical section shingles. The ablation samples were added only as an experimental study, which is discussed in the section entitled "Scientific Experiments," and were not installed with the intention of altering the effectiveness of the beryllium shingles for this mission.

All temperature data, as recorded from thermocouples located around the exterior of the spacecraft, were within expected ranges and were in excellent agreement with measurements taken during previous orbital missions (see refs. 1 and 2).

 

Mechanical and Pyrotechnic System

 

The mechanical and pyrotechnic systems consist of the separation devices, the landing system, the rocket motors, and the internal spacecraft structure. These systems functioned normally throughout the mission. The configuration of these systems was nearly identical to that of the previous orbital missions. The notable changes from the MA-7 mission were the removal of the heater blankets from around the retrorocket motors in order to conserve weight and the addition of a SOFAR bomb to be ejected at main parachute deployment and detonated at 2,500 feet below the surface of the water to assist in the location of the spacecraft after landing.

The primary separation interfaces are those between the spacecraft and the escape tower, between the spacecraft and the launch vehicle, at the heat shield, and around the spacecraft hatch. All separation devices performed effectively during the mission, including the [3] explosive-actuated side hatch which was deployed by the astronaut after the spacecraft had been placed on the deck of the recovery ship.

The landing system includes the landingshock attentuation system (landing bug) and the drogue, main and reserve parachutes. These systems were unchanged from MA-7 spacecraft configuration. The landing system performed satisfactorily the drogue parachute was deployed manually as planned at a pressure altitude of 39,400 feet, and the main parachute sequence was initiated automatically at a pressure altitude of 10,600 feet, which was within specification limits. The only incident of an anomalous nature was the slight. tearing of the main-parachute deployment bag. Both the drogue and main parachutes performed properly and were undamaged during descent.

The escape, posigrade, and retrograde rocket motors operated satisfactorily, and their thrust levels were within specification limits. The internal spacecraft structure was found to be entirely normal during the postflight inspection.

 

Spacecraft Control System

 

In accomplishing the task of providing attitude and rate control of the spacecraft during the orbital and reentry phases, the spacecraft control system performed satisfactorily throughout the entire flight. The control system was essentially equivalent to that which was installed in the MA-7 spacecraft with but minor changes. These changes include widening the limit cycle or deadband of the automatic stabilization and control system (ASCS) in the orbit mode from ± 3° to ± 5.5° to conserve fuel, incorporating an "attitude select" switch for maintaining either retroattitude or reentry attitude in the orbit mode of ASCS, providing a switch to disable the high (24-pound) thrusters in the fly-by-wire mode during normal orbital operations (see fig. 1-2), and installing a modified cover for the pitch horizon scanner to alleviate possible thermal effects during ascent. An automatic feature existed which made the high thrusters operative at retrofire when using fly-by-wire to provide rapid spacecraft alinement and to control any angular rates which might occur.

 


Figure 1-2. Fly-by-wire thrust-select-switch modification.

 

Control System Electronics

 

One unexpected occurrence of minor significance during the flight was that the deadband obtained with the ASCS; was greater than expected. For example, the deadband was approximately ± 8° for the initial thrust pulse instead of the planned ± 5.5° mentioned previously. The exact reason for this anomaly is unknown, but preliminary studies indicate that the duration of the thrust pulses at the given attitude limits was less than expected. This disparity did not adversely affect control system performance or control fuel usage.

Brief voltage transients were indicated across the solenoid valves for the 24-pound automatic system thrusters when the astronaut switched from ASCS orbit mode to another method of control, but these transients were insufficient to operate the solenoid valves and are, therefore, not considered to have been of a serious nature.

 

Fuel Usage

 

The usage rate of hydrogen peroxide control fuel was less than had been predicted for the MA-8 mission. The mission has been planned for minimum fuel usage, a philosophy u-which was incorporated into the schedule of inflight activities, and the astronaut adhered strictly to this flight plan. This result is especially satisfying when the fuel usage of the two previous flights is compared with that of the MA-8 mission, which was of much longer duration The time history of fuel remaining for the MA-8 flight is presented in figure l-3. Although no additional fuel was included, a number of minor changes in equipment and flight procedures contributed to the increased fuel economy. The addition of a switch to disable the high thrusters when they were not needed permitted the pilot greater freedom in stick motion, since he then was not required to restrain his hand movement within a fixed range to activate only the economical low thrusters. This switch, therefore, eliminated the possibility of inadvertently using the fuel...


Line graph of the Fuel usage rates

[4] Figure 1-3.-Fuel usage rates.

...costly high thrusters during situations in which the pilot's attention might be distracted. The widening of the ASCS deadband was done in an effort to reduce the number and duration of control pulses per unit time and, therefore, the amount of total fuel consumed. The primary technique to reduce fuel consumption, however, was the fact that the flight procedure included long periods of attitude-free drifting flight. During some of these periods, very small quantities of fuel were used at times to maintain spacecraft attitudes within the limits of the horizon scanners. When it was important to have the spacecraft at retroattitude for a possible mission abort, the ASCS orbit mode, which involves very small quantities of fuel, was utilized. Finally, the flight plan intentionally excluded control maneuvers which would have caused large quantities of fuel to be consumed. It must be emphasized, however, that the previously mentioned factors were complementary to the pilot's discreet management of control system operations, for which he alone was responsible. Astronaut Schirra's discipline in using control fuel was the primary reason for the favorably low rate of expenditure.

 

Communication Systems

 

Performance of the spacecraft communication systems throughout the entire mission was satisfactory. The communication systems used in the spacecraft for the MA-8 flight were very similar to those employed for the two previous orbital missions. There were, however, some notable changes from MA-7. The voice system included a more sensitive and effective microphone in the astronaut's helmet (fig. 1-4), a dipole antenna (fig. 1-5) to be used for orbital high-frequency (HF) voice communications, a hardline link from the spacecraft to the liferaft for possible use after landing, and a miniature ultra-high-frequency (UHF) transceiver which [5] was added to the survival kit in the liferaft. The HF recovery transceiver was removed for the MA-8 mission. In addition! one of the two previously used command receivers and....

 


[MISSING] Figure 1-4.-Closeup photograph of microphone installed in the helmet.

 

....decoders was removed in an effort to save weight, since these units have exhibited a high reliability in previous missions. The astronaut had the capability to switch the HF transceiver to either the standard bicone antenna or the dipole antenna.

 

Voice Communications

 

During the launch phase, the background noise caused triggering of the voice-operated relay within the spacecraft transmitter which precluded reception in the spacecraft for brief...

 


[MISSING] FIGURE 1-5.-High-frequency dipole orbital antenna.

 

...periods of ground-to-air communications. This triggering or keying was apparently the result of the increased sensitivity of the new microphone installed in lieu of the two less efficient units previously flown. During the orbital phase, the range of HF reception and transmission w as considerably improved over that of previous orbital missions, undoubtedly as a result of the new HF orbital antenna. Most of the ground stations around the Mercury Worldwide Network reported effective HF and UHF voice contact with the astronaut, who also reported that reception from all stations was exceptionally good.

 

Radar Beacons

 

The performance of the C- and S-band radar beacons was satisfactory, for the MA-8 flight, but the C-band beacon experienced slight amplitude and frequency modulation, as in previous missions. This condition, caused by the phase shifter and, at times, poor antenna orientation during tracking operations, is not significant. Good tracking data were acquired whenever the spacecraft was over a station with the beacons on; however, no usable tracking data were received during the periods when the beacons were turned off.

The recovery forces reported that transmissions from all location aids, with the exception of the SEASAVE HF rescue beacon, were satisfactorily received. The SEASAVE beacon was tested after the flight and operated within specification. The reason for this lack of signal reception is believed to be shorting of the recovery antenna. The flashing recovery light was also reported to have stopped operating during the recovery period, but postflight tests to date have revealed no malfunctions in this unit; however, the investigation is continuing.

 

Command Receiver

 

Although it was not required for flight control during the mission, the command receiver operated normally during the launch and orbital flight phases. Calibration signals for correcting baseline shifts in the instrumentation were satisfactorily received by the spacecraft. However, during the deployment of the drogue parachute, an all-events-channel indication with a signal strength of 3 microvolts was noted. This indication was of no significance to the [6] mission and is believed to have been caused by the planned delay in the deployment of one of the radio antennas.

 

Instrumentation System

 

Performance of the instrumentation system was satisfactorily, with but a few minor anomalies, for the MA-8 flight. The system was nearly identical to configurations used during previous orbital missions. Because of the extended duration of this flight, the program for operation of the astronaut observer camera was modified and the thickness of the magnetic recording tape was reduced to provide full mission coverage. Additional changes include the substitution of all impedance pneumograph for the breath-sensing thermistor used in MA-7 to measure the astronaut's respiration and the relocation of the temperature monitoring point for the environmental control system from the steam vents to the domes of the heat exchangers. Finally, an indicator was added to the instrument panel to display oxygen partial pressure in the cabin, and the coolant-quantity-indicator transducer was removed.

While conducting a launch simulation prior to flight, the 108-second timer which terminates the automatic sequence of the blood pressure measuring system (BPMS) failed to operate. Since the BPMS could be stopped manually, prelaunch operations were continued without replacing this unit because of the time involved. Postflight analyses revealed that a faulty switching transistor in the timing circuit was the cause of the malfunction.

On the day prior to launch, the body temperature readout on the high-frequency telemetry channel became slightly noisy, but a decision to continue into the launch countdown was made because the low frequency channel was yielding good data. However, at 6 minutes before lift-off, both channels of the body temperature readout became erratic. A decision to continue with the mission was again made, since the suit-inlet temperature and the astronauts status report were deemed to be satisfactory. The loss of body temperature measurement continued until just prior to 02:00:00 ground elapsed time (g.e.t.), after which the readings were in the normal range, with some intermitted readings, until completion of the flight. Exhaustive postflight testing has not revealed any malfunctions which would explain the temporary loss of this instrumentation.

During the flight, there were discrepancies between the suit-inlet temperature indications displayed to the astronaut and those transmitted to the ground over the telemetry channels. The ground readout was as much as 8° F higher than that reported by the pilot at times during the flight and improper calibration and interpretation of the temperature pickup is believed to have been the source of the error. These and other smaller discrepancies are currently under investigation.

Some erratic behavior of the oxygen partial pressure transducer was evident during the mission. For a period of about 15 minutes, beginning at 01:14:00 g.e.t., the partial pressure indications were of no value, and, thereafter, poor quality data for periods of up to 30 seconds were occasionally exhibited. Postflight duplication and analysis of this erratic behavior were not possible because of the expiration of the lifetime of the instrument sensor.

 

Life Support System

 

The life support system primarily controls the suit and spacecraft cabin environments, but the system also includes the food, water, pressure suit, and restraint system for the astronaut. This system performed satisfactorily and was of a configuration similar to those of previous manned orbital flights except for the following notable differences. The molded leg restraints were removed, and only small lateral supports at the knees and toe-and-heel restraints were installed. The manual lockout feature of the cabin pressure relief valve was deleted. Because the mission was extended, it was specified that the cabin leakage rate was not to exceed 600 cc/min before lift-off to conserve cabin oxygen during the flight, and 15 pounds of coolant water were added to the environmental control system (ECS). The final change to the life support system was the inclusion of eight radiation dosimeters, five of which were of a solid-state type installed in the pressure suit and the remaining three versions were self-indicating to permit inflight monitoring by the astronaut.

Although the ECS performed satisfactorily throughout the mission, its cooling performance...

 


Line graph of the Suit-inlet temperature and coolant-control-valve setting

[7] FIGURE 1-6.-Suit-inlet temperature and coolant-control-valve setting.

...in the suit circuit was not entirely satisfactory during the first 2 hours after launch. Cooling in the pressure suit was somewhat less than expected after orbital insertion, but a gradual advancement of the coolant control valve (CCV) by the astronaut adequately corrected this situation. The launch setting of 4.0 for the suit-circuit CCV was established from preflight tests, but after this setting proved to be insufficient for proper cooling, subsequent inflight increases in half-position increments were made to a level of 7.5. This increased level of coolant flow resulted in more satisfactory- suit-inlet temperature and was essentially maintained throughout the remainder of the flight as shown in figure 1-6. Postflight tests revealed that dried lubricant had partially blocked the valve orifice and reduced the flow. This reduction in flow shifted the preflight calibration curve so that the CCV setting at launch was no longer valid for proper ECS operation in orbit. Effective monitoring and management of the ESC by the astronaut resulted in satisfactory control of the suitcooling circuit.

As also experienced during the MA-7 flight, the cabin temperature was slightly above the desired level, but was still well within acceptable ranges. Flight data indicated that the cabin heat exchanger was operating efficiently during the flight. Drifting flight provided the astronaut with the capability to reduce cabin temperature by shutting down heat-producing components. Because of increased heat loads since the original design of the cabin cooling circuit, the temperature levels are now above those initially specified but are considered nominal for this flight.

 

Electrical and Sequential Systems

 

The electrical and sequential systems performed extremely well throughout the MA-8 mission, and only very minor problems were encountered. These systems were essentially unchanged from the MA-6 and MA-7, missions. However, the zener diode panel used on previous flights was removed to eliminate voltage transients, a number of relatively small but significant modifications were made as a result of a single-point failure analysis, and the control barostat used for deploying the landing system in the MA-7 spacecraft was removed. Each of the remaining sets of barostats in the parachute deployment circuit was wired in series for improved reliability.

During the flight, the rate of increase in the operating temperature of the 250 volt-ampere inverter indicated that little or no cooling was present for that unit. The temperatures of this inverter were, however, within acceptable limits and caused no concern on the ground. Postflight tests showed the coolant-flow orifice for this inverter to be partially blocked.

A very brief delay was reported by the astronaut in the ignition of the first retrorocket. Postflight investigation of the sequential ignition circuitry disclosed no malfunctions, and a close examination of the flight data provided verification that the timing unit operated within specification limits. The nominal retrosequence period is 30± 0.5 seconds in length, and the [8] data show that the corresponding duration for MA-8 did not exceed 30.5 seconds.

 

Scientific Experiments

 

Four scientific experiments were planned for the MA-8 mission which utilized equipment and materials in addition to the normal spacecraft operation. These experiments were a continuation of the program initiated during the MA-6 mission to study the scientific aspects of terrestrial space. The experiments to be discussed include two which required the participation of the astronaut and two which were of a passive nature.

 

Light Visibility Experiment

 

As in the MA-6 and MA-7 missions, an attempt was made by the astronaut to observe high-intensity light sources at ground-based locations. The objective for this experiment, as in MA-7, was to determine the capability of the astronaut to acquire and observe a ground-based light of known intensity. Another location, in addition to Woomera, Australia, was provided at Durban, South Africa. During the first orbital pass over Woomera, Astronaut Schirra was to acquire visually the light from four flares, each with an intensity of 1 million candlepower. At Durban, he was to observe a xenon light of similar intensity for a period of about 3 minutes during the sixth orbital pass. Both attempts were unsuccessful because of extreme cloud cover. The astronaut reported that, although cloud formations were prevalent around the entire ground track of the orbit, he was able to see lightning in a storm over Woomera and the lights of a city near Durban while conducting the experiment.

 

Photographic Studies

 

A 70-mm Hasselblad camera with detachable film magazines and filters was used in two studies of photographic and spectral definition of terrestrial surface features. Since a prescribed ground rule of the flight was to conserve control fuel, only a few selected photographs were taken.

The U.S. Weather Bureau sponsored a photographic exercise which involved exposing the film through a special filter mosaic. The purpose of this exercise was to measure the spectral reflectance of clouds, land, and water for application to weather satellites. The filter mosaic, shown in figure 1-7 and described in the following table, consisted of six gelatin plates which were mounted just ahead of the film plane in a special magazine.

 


[MISSING] FIGURE 1 - 7.-Filter mosaic slide.

Number

Color

Wratten number

Neural density of W-96 filter

1

Blue

W-47B and W-96

0.1

2

Green

W-61 and W-96

0.1

3

Neutral

W-96

0.2 and 0.9

4

Yellow

W-15 and W-96

0.9

5

Red

W-25 and W-96

0.6

6

Far red

W-70 and W-25

-

 

A total of 15 frames were exposed on the U.S. Weather Bureau films by the astronaut, and a preliminary postflight analysis indicated that the yellow and red filters yielded a higher contrast than the other filters, as shown in figure 1-8. Although certain controls were exercised prior to launch, such as measuring the spectral transmittance of the camera lens and spacecraft window, the astronaut reported that, when the escape tower was jettisoned, the exhaust of the rocket left a light residue of...

 


[
9] [MISSING] Figure 1-8 .-Weather photograph showing fiIter comparison.

 

...indefinable characteristics on the window. An investigation of the effect of this residue on the photographs, a comparison of these photographs with some which were taken on the day of launch by the Tiros satellite, and further analysis of the exposures are being conducted.

A series of terrestrial color photographs were taken by Astronaut Schirra for two purposes: (1) to aid in building up a catalog of space photographs of various physiographic features of the earth, such as folded mountains, fault zones, and volcanic fields; and (2) to obtain photographs of cloud patterns for comparison with those of other satellite programs. An exposure meter was provided the astronaut to aid in the adjustment of the camera. A total of 14 exposures was made over the western United States and Mexico during the third pass and over South America during the sixth pass. Several of these photographs were either overexposed or rendered unusable with regard to physiographic studies because of extensive cloud cover. An analysis of the remaining frames is in progress.

 

Nuclear Radiation Experiment

 

Two packages of radiation-sensitive emulsions were provided by the NASA Goddard Space Flight Center to study the flux and composition of the galactic cosmic radiation outside the Earth's atmosphere. It was also intended that, a measurement of the intensity and energy spectrum of artificially induced electrons at orbital altitudes to be obtained. The processing of these emulsions consumes an extensive amount of time; however, a preliminary inspection of the plates indicates that valuable data will be derived from both film packages.

In addition to the Goddard emulsion packages, two sets of radiation-sensitive films, which have been included in spacecraft for previous missions, were provided by the U.S. Naval School of Aviation Medecine. These [10] emulsions will also be analyzed to provide a continuing catalog of radiation data for the near-space environment.

 

Ablation-Material Investigation

 

An experiment intended to determine the reentry heating effects on various advanced ablation materials was conducted during the MA-8 mission. These materials are being considered for possible use in the design of vehicles for future space programs. Although many studies of these materials have been conducted in the laboratory , the Mercury mission afforded the opportunity to use much larger test samples under more realistic conditions. A total of eight types of ablation material in nine different configurations was supplied by six organizations. These samples were bonded to the exterior surface of 9 of the 12 beryllium shingles on the cylindrical section of the spacecraft. A preflight photograph of these materials bonded to the shingles is shown in figure 1-9. Two of the uncoated shingles were instrumented with thermocouples, and temperature-sensitive paint was applied to the interior surface of each of the nine experimental shingles. The ablation panels were each 15 inches long and 5 inches wide. Most of the samples contained intentional cutouts to represent repairs and joints in order to determine the effectiveness of modification and restoration techniques for these materials.

A close inspection of the panels following the flight revealed evidence of normal charring and some minor cracking, as expected, but there was no indication that delamination from the beryllium shingles occurred. The ablation panels received little damage during postflight handling, and each of the samples appears to have sustained the reentry heat pulse in excellent fashion. An initial inspection of the areas which had received purposeful repairs shows that they were no more affected by reentry heating than other portions of the ablated surfaces. An analysis of the temperature data and a more detailed investigation of the ablation samples are continuing.

 

Launch Vehicle Performance

 

The Atlas (113 D) launch vehicle which placed Astronaut Schirra and his Sigma 7 spacecraft into an orbit having a perigee altitude...

 


[MISSING] FIGURE 1-9.-Ablation material samples bonded to spacecraft beryllium shingles.

 

...of 100 miles performed exceptionally well. A significant hardware change since. the MA-7 mission was included for this flight. The two booster engines were modified to include new baffled fuel injectors which improved the combustion characteristics, and hypergolic igniters were installed in lieu of the pyrotechnic devices previously used. Because of these modifications, the rough combustion cutoff capability and the hold-down delay used in the past to allow for monitoring engine performance immediately after ignition were discontinued. In addition to this change, the insulation bulkhead, which was considered to be unnecessary [11], was removed at the factory. Finally. the hydraulic lines associated with the pressure transducers of the abort sensing system in the thrust section were modified to prevent freezing, a condition believed to have existed during MA-7 (see ref. 2).

All launch vehicle systems performed satisfactorily, and only two minor anomalies occurred which should be noted. The trajectory of the launch vehicle prior to booster engine cutoff was somewhat lofted, and this condition resulted in an early staging of the booster engines and a late sustainer engine cutoff (SECO). In addition, a slight overspeed condition of 15 feet per second at insertion resulted in the apogee altitude of the orbit being about 8.6 nautical miles greater than nominal. The guidance system operated within specification, and all guidance parameters were acceptable during the go-no go computation immediately after SECO.

A small clockwise roll transient occurred immediately after lift-off, and this roll rate probably was caused by a slight misalinement of the booster engines and thrust from the gas generator exhaust. The magnitude of the roll transient was less than the abort threshold value, and the condition was satisfactorily corrected by the vernier engines of the launch vehicle.


References

1. Staff of NASA Manned Space Center: Results of the First United States Manned Orbital Space Flight, February 20, 1962. Supt. Doc., U.S. Government Printing Office (Washington, D.C.).

2. 1. Staff of NASA Manned Space Center: Results of the Second United States Manned Orbital Space Flight, May 24, 1962. NASA SP-6, Supt. Doc., U.S. Government Printing Office (Washington, D.C.).


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