THE hypervelocity research laboratory was completed in 1961 at a cost of about $1 million. This laboratory became the home of the Physics Branch, which carried on with ion-beam studies begun in 1957-1958 by Michel Bader and with the investigation into the properties of gases at high temperatures earlier initiated by Fred Hansen. This work was becoming increasingly important, and was both fundamental and applicable to current practical design problems.
The 3.5-foot tunnel, also completed in 1961, was equipped with interchangeable nozzles for operation at Mach numbers of 5, 7, 10, and 14. No longer was it considered feasible to provide variable-geometry nozzles for wind tunnels designed. to operate at high speeds and temperatures. In the 3.5-foot tunnel a tremendous pebble-bed heater had been incorporated with the expectation that it would preheat the air to 4000° F and thus prevent liquefaction in the test section. Unfortunately, the heater was able to provide air temperatures of only 3000° F and the use of the Mach 14 nozzle was thus precluded.
The unexpected limitation on the performance of the pebble-bed heater arose, in part, from a chemical and structural instability of the refractory material (various mixtures of zirconia, alumina, calcia, etc.) produced, at high temperature, by a migration of its constituents. Additionally, the relative motion of the pebbles arising from thermal expansion produced refractory dust that sandblasted the finely polished tunnel throat and test model. Different refractory materials were tried as were also various arrangements and combinations of these materials. By the end of 1962 no solution to the problem had been found other than to accept, for the time being, the lower operating temperature and speed.
The item which had been proposed in 1958 as a 12- by 12-inch helium tunnel was completed late in 1960 and actually turned out to be a 20-inch-square helium tunnel. At the same time, a 14-inch helium tunnel was built....
....in the 3.5-foot-tunnel building. The 14-inch tunnel was built at very little cost inasmuch as the 3.5-foot tunnel was already equipped with a helium processing plant, helium storage facilities, and much of the piping required. All that was required were some simple nozzles.
Both the 14-inch and the 20-inch helium tunnel were equipped with alternate nozzles for operating at Mach numbers of approximately 10, 15, 20, and 25. Such high Mach numbers were easily achievable with helium inasmuch as heating was not required to avoid liquefaction. Because of the ease with which the helium tunnels could be operated, they were often used to run tests that would simplify and shorten test programs scheduled for the more cumbersome and expensive 3.5-foot tunnel. The limitations of helium for simulating air in a wind tunnel were also examined. It developed that helium test results are highly questionable in cases where: (1) a complex pattern of intense shock waves is present, (2) an occluded pocket of subsonic flow exists in an otherwise supersonic flow pattern, and (3) the ratio of skin friction to pressure drag is high.
Another facility completed and put into use in 1960 was the 1-foot hypervelocity shock tunnel on which Bernie Cunningham and his colleagues had spent so much development time. This tunnel was originally intended to be a part of a new hypervelocity atmosphere-entry simulator named the parabolic entry simulator, or PES. The PES was assembled but inasmuch as the need for the device was disappearing and the difficulties of operating it were great, the project was abandoned before the simulator was ever used  The shock tunnel, however, was felt to be useful for other test purposes and thus it was installed in an old Quonset hut construction shack, which was glorified by the name of "hypervelocity airflow laboratory," just north of the 6- by 6-foot tunnel.
Described in TN D-1428 by Cunningham and Kraus, the shock tunnel consisted of a driver tube which was separated by a diaphragm from a shock tube which in turn was separated by a second diaphragm from a nozzle and supersonic throat. The throat was connected to a large evacuated vessel which received the gases flowing from the tubes. In operation, the driver tube was filled with an explosive mixture of hydrogen and oxygen gas together with a certain amount of helium for softening the explosion. The shock tube was filled, under pressure, with air or any other test gas which might be required to simulate the atmosphere of, for example, Mars or Venus. The combustible gases, ignited by an electrically heated wire, built up a pressure that burst the first diaphragm and caused an intense shock wave to race down the shock tube. The shock waves, both direct and repeatedly reflected, heated and pressurized the test gas to such a degree that it burst the second diaphragm and flowed past a test model mounted in the supersonic throat.
The 1-foot shock tunnel was capable of producing flows lasting up to 100 milliseconds or more at Mach numbers up to 14. Enthalpies ranged up to about 4000 Btu per pound. Operation of the tunnel required considerable preparation and only one shot could be made in an 8-hour shift. Adding to the operating time and difficulties was the mess caused by the water generated during a shot. This water was, of course, the condensate of the steam produced by the combustion gases.
The use of a shock tunnel in counterflow arrangement with a light-gas gun had been pioneered in 1958 with the somewhat reluctant approval of Ames management by Tom Canning and Al Seiff. The pilot hypervelocity free flight facility (pilot HFF facility), as the first device of this kind was called, was built of spare parts from around the Center and was fairly crude; but it demonstrated the soundness of the principle. There had been much questioning of the feasibility of such a device in view of the timing problems involved in making successful measurements. The principle of the HFF facility having been proved, Tom Canning and a few others at Ames wished to proceed immediately with the development of larger and more sophisticated HFF facilities capable of providing speeds, densities, and enthalpies corresponding to those encountered by a spacecraft returning from an earth orbit, a trip to the moon, or even a voyage to one of the planets. The HFF principle seemed the most likely of any yet developed to satisfy these simulation requirements. It appeared, however, that Ames management was not  sufficiently well sold on the HFF idea to embark on this expensive enterprise without additional preparatory work. As a result Ames invested about $350,000 in a prototype HFF facility which was completed in 1961. This facility, which like the pilot HFF facility was located just south of the 1- by 3-foot tunnel, was approximately 200 feet long-much larger than the pilot facility. It incorporated a two-stage shock-compression gun that produced speeds of more than 20,000 feet per second and a shock tunnel that produced an air pulse having a speed of up to 15,000 feet per second. The maximum relative speed between air and model approached 40,000 feet per second, while the achievable stagnation enthalpy was greater than 30,000 Btu per pound and the Reynolds number per foot was over 1 million. The tunnel was designed for a modest Mach number of 7 in order to maintain the air density at a fairly high level. It will be recalled that a high density as well as a high enthalpy is necessary for the simulation of aerodynamic heat
The performance of the prototype HFF facility proved satisfactory and shortly Seiff and Canning submitted a proposal for a huge new HFF facility that would cost about $5 million.
The Ames Research Center was now taking a substantial interest in the effects of meteoroid strikes on spacecraft. Although Ames had already built three ballistics ranges in which such studies could be made, it was decided that a fourth range should be designed specifically for terminal ballistics work. The principal requirement for a range of this nature would be a gun of such size and power as to generate the highest possible launching speed. As in the other ranges, the gun, target, and test section would be enclosed in a single tubular chamber that could be evacuated to represent high-altitude conditions or filled with gases typifying various atmospheres.
The new range, named "impact range," was built in 1961 and first put to use in 1962. It was located with the other three (Janus, pilot, and main) ranges in the range building which had been constructed along the western border fence. The impact range thus became a part of a complex of four facilities that together were known as the hypervelocity ballistics range (HBR) The HBR was operated by the HBR Branch originally headed by Alex Charters and, after Charters left in February 1961, by Tom Canning.
Inasmuch as the gun was perhaps the most important element in a range or a hypervelocity free-flight facility, it became the subject of an intensive and continuing development program. The Bioletti-Cunningham  shock-driven gun was relatively simple and generated launching speeds of around 20,000 feet per second but unfortunately it was not really suitable for launching heavy models. The Charters-Rossow-Denardo piston-compressor gun could launch heavier models, but launching speeds were limited to about 13,000 feet per second and, in any case, the gun was mechanically and otherwise impracticable in its existing form. The practicability of the gun could be increased, of course, by closing the breech and eliminating the reaction piston which, most disconcertingly, flew out of the rear end. This change would get rid of some of the more serious complications but even so the gun just did not have enough "zock" to produce the desired high launching speeds.
The main problem of the piston-compressor gun was that a small pocket of gas had to be left at the end of the driver tube to act as a shock absorber for the heavy metal piston. Otherwise the piston would slam into the end of the smaller launch tube with a devastating wallop. The pocket of gas, though useful as a shock absorber, introduced a thermodynamic, or volumetric, type of inefficiency that took the edge off the piston's thrust. It softened the blow as does the clearance volume in the cylinder head of an automobile engine. What was needed was a means for closing out that volume while still obtaining shock absorption.
The solution to this problem was found by a young man named John Curtis who had recently joined the Ames staff. Curtis decided that what was needed was a semi-soft plastic piston that deformed on impact and thus acted as its own shock absorber. He believed, moreover, that the shock-absorbing action could be made still smoother if the last portion of the driver tube was made slightly conical (tapered) so that the soft-nosed piston, while coming to rest, would squeeze down and completely fill the cone. The nose of the piston, Curtis believed, would actually "squirt" forward, generating the highest possible pressure and driving the last bit of gas into the launching tube.
The idea proposed by Curtis was tried and proved immensely successful. The deformable-piston gun quickly demonstrated its ability to generate launching speeds as high as, or higher than, those of the shock-driven gun. John Curtis had really saved the Charters gun from extinction. The new Charters-Curtis deformable-piston, light-gas gun was destined to become the standard at Ames and, good though it originally was, its performance was continually increased by later refinements. Also, its efficiency was found to increase with its size. In the course of the gun's development, many different piston shapes and materials were investigated, with polyethylene becoming the favored material. Some of the pistons were made with an internal cavity containing water. The gun design ideas originated by Curtis are described in his report TN D-1144 (ref. C-1), "An Accelerated Reservoir Light-Gas Gun."
The HFF Facility could, perhaps more accurately than any other device, simulate the aerodynamic and heating conditions experienced by reentry spacecraft. Nevertheless it had a number of faults, one of which was the short period of time over which the simulated conditions prevailed. Not only did this fault introduce severe operational difficulties but, even worse, it precluded the use of the facility for simulating certain aerodynamic and heating processes that required more than a few milliseconds to reach an equilibrium stage. One of these processes, unfortunately, was the thermochemical process of ablation, which at this time was regarded as the most promising means for protecting spacecraft from the ravages of reentry heating.
Ablation was a mass-transfer cooling process, like sweat cooling, in which a solid material with which a spacecraft could be coated would absorb heat by the physical processes of melting, evaporation, and sublimation; the material thus transformed would gradually be dissipated into the surrounding airstream The choice of ablation material depended on the rate and duration of the heating pulse, and materials such as plastics (e.g., Teflon), quartz, and graphite appeared useful for this purpose.
The physical processes of ablation had been found to proceed with sufficient rapidity to allow them to be investigated in counterflow devices such as the atmosphere-entry simulator; indeed, that was the main function of the AES and the intended function of the abandoned parabolic entry simulator. Often, however, there were chemical reactions between the ablator  and the boundary layer that proceeded rather slowly and could not be investigated in short-period test devices of the HFF or the AES type. These reactions were prevalent in ablators that formed a surface char layer through the pores of which the vaporized ablation material percolated. It was for the investigation of charring ablators that a special test device was needed. That device was the arc-jet tunnel.
The development of the arc-jet at Ames was a complex and very import tent process that began in 1956, rapidly increased in intensity during the early years of NASA, and continued thereafter at a high level. It began with the preliminary study and applications of the few available commercial arc heaters (such as Plasmadyne) and continued with the development of a series of increasingly refined arc-jets that represented a major contribution both to arc-jet technology and to aerothermodynamic research. Early contributors to this work have already been named. Others who contributed in the 1959-1962 period included Glen Goodwin, Howard Stine, Charles Shepard, Velvin Watson, Roy Griffen, Ernie Winkler, Warren Winovich, and Brad Wick.
The arc-jet, or arc-jet tunnel, though sometimes of the continuous-flow type, is typically a supersonic blowdown tunnel in which air, or any other gas, from a pressure vessel is released to flow through a supersonic throat, over a test model, and into an evacuated receiving chamber. Running time is usually from one to several minutes. On its way to, or through, the supersonic throat, the air is heated by a powerful electric arc. One of the major problems in the design of an arc-jet is to arrange an intimate mingling of the airstream with the arc so that the heat of the arc is transferred to the air. The problem is difficult because the air seems to want to avoid the arc. Another critical problem in arc-jet design is to keep the whole unit, particularly the sonic nozzle and the electrodes, from melting. Water cooling, sweat cooling, and other means are used. Contamination of the airstream by vaporized electrode material must also be minimized. Such partial solutions to these problems as were available had required years of imaginative development work.
The first arc-jet units developed at Ames were completed in 1960. Their electrodes were in the form of hollow, water-cooled concentric rings over which the air passed on its way to the sonic nozzle (constriction) of the supersonic throat. A magnetic field was used to move the arc around the rings so that it would not cause excessive heating and erosion at any one point. One of these concentric-ring arc-jets was able to add 1500 Btu to each pound of air passing through it while operating at 100 atmospheres air pressure with an arc power of 2 megawatts. At low pressures (less than 1 atmosphere), the heat, or enthalpy, added to the airstream was as much as 9000  Btu per pound. The first published information on Ames concentric-ring arc-jet development work was the paper "Electric Arc Jets for Producing Gas Streams with Negligible Contamination," by C. E. Shepard and Warren Winovich This paper was presented in 1961 at a meeting of the American Society of Mechanical Engineers and published as ASME Preprint 61WA-247.
The enthalpy of 9000 obtained with the concentric-ring arc-jet did not, of course, represent spacecraft reentry conditions. A much more efficient transfer of heat from arc to air was needed. Howard Stine and Glen Goodwin bent their minds to this problem. The heat-transfer efficiency would be much higher, they figured, if the air and the arc were forced to commingle by passing them both through a narrow constriction in the airflow passage. The cathode would thus be upstream of the constriction, the anode downstream, and the arc would pass lengthwise through the constriction. This device was known as the "constricted arc."
The constricted arc was not new in principle but its successful development, as carried out by Howard Stine with the help of Charles Shepard and Velvin Watson, was a major accomplishment and produced a revolution in arc-jet design. With this work the potentiality of the arc-jet for simulating intense aerodynamic heating was much enhanced. Stine's classical work on the constricted arc represented a beautiful blending of theory with experiment. The theory is contained in TN D-13.31 (ref. C-2), "The Theoretical Enthalpy Distribution of Air in Steady Flow Along the Axis of a Direct-Current Electric Arc," by Howard A. Stine and Velvin R. Watson.
In the first constricted arc-jet, initially operated in the fall of 1961, the arc was made to pass through a short constricted throat which was installed in the airflow passage ahead of the sonic throat. This unit, as described in a paper which Glen Goodwin delivered in Paris in 1962, produced enthalpies....
 .....up to 12,000 Btu per pound with an arc power of 2.5 megawatts at an airflow of 0.1 pound per second and 7 atmospheres pressure. The tests confirmed the theory of Stine and Watson, yet it appeared that the performance of the unit was handicapped by the fact that the heat, in effect, was being trapped in the plenum chamber ahead of the sonic nozzle. If the heat could be added to the air as it passed through the sonic nozzle, it was believed a better result could be achieved. If then the sonic nozzle were lengthened to prolong the contact between the arc and the air, a large improvement in performance might be expected. One problem, of course, was to prevent the arc current from passing through the walls of the elongated sonic throat rather than through the air passage. This problem could be solved, it was found, by constructing the nozzle of thin, transverse, water-cooled segments or laminations separated from each other by insulating material in the form of boron nitride washers. Boron nitride was a good electrical insulator yet provided some thermal conduction.
The principles just mentioned were incorporated in a new unit called the supersonic arc plasma jet:, which was designed and built in 1962. Preliminary tests with this unit indicated that enthalpies of 30,000 Btu per pound could be obtained. The arc-jet had now proved itself ready for research use; in fact, some research had already been performed with Plasmadyne and concentric-ring units. At this stage, late in 1962, a number of papers on arcjet technology were being prepared by such authors as Howard Stine, James Jedlicka, Charles Shepard, and Velvin Watson. An earlier Ames paper, presented in 1962 at the Second Symposium on Hypervelocity Techniques, was entitled "A Wind Tunnel Using Arc-Heated Air for Mach Numbers of 10 to 20," by Forrest E. Gowen and Vaughn D. Hopkins.
A Plasmadyne arc heater was incorporated in 1959 or 1960 into the 8-inch low-density wind tunnel and later two complete arc-jets, of the concentric-ring type, were installed in the 1- by 3-foot wind-tunnel building, now called the fluid mechanics laboratory. Later, two constricted-arc units were installed in flow channels in the old low-density heat-transfer building, now called the space technology building. These installations were small and mostly of an experimental character, but Glen Goodwin and Dean Chapman had come to the conclusion that the arc-jet offered sufficient promise to justify the construction of a major facility to exploit the device for studies of ablation and other heating phenomena. Glen and Dean each prepared specifications for the facilities they had in mind and when later these were combined and submitted to Ames management, the estimated cost of the proposed "mass transfer and aerodynamics facility," as it was called, was $15 million. Smitty DeFrance was not very enthusiastic about the proposal, and Jack Parsons knocked the allowable price down to $5 million. The proposal....
....was then submitted to NASA Headquarters, where Ira Abbott, head of OART at the time, cut the price to $4 million, at which level it was approved. The facility, now called the "gasdynamics laboratory," was put under construction in 1960-1961 and completed in 1962. It was located just north of the Unitary Plan wind tunnels.
The gasdynamics laboratory designed for the exploitation of the arc-jet consisted not so much of the arc-jets themselves as of the mighty auxiliaries necessary to operate arc-jets of any reasonable kind or size. Positions were provided in the facility for the installation of three separate arc-jet units. Of the $4 million spent on the gasdynamics laboratory, approximately $1.7 million went for air-handling auxiliaries (evacuator and collector), another $1.36 million was spent on the 15-megawatt electrical power supply, and the remainder, nearly $1 million, was invested in wind-tunnel controls, data-handling facilities, and building. The facility so constructed had a great deal of operational flexibility and was well suited for the purpose intended: the further development of arc-jets, fundamental studies of ablation, and the effects of ablation on the aerodynamic characteristics of reentry bodies. It was not long before concentric-ring and constricted-arc-jets were installed and operating in the new laboratory.
Flight simulators were at this time beginning to take on the character of major facilities. The analog-computer elements associated with the simulators already had become quite extensive. In 1960 it was found desirable to assign responsibility for these elements, and all of the other simulator hardware, to a special group. This group, headed by John Dusterberry, was the Analog and Flight Simulator Branch of the Full Scale and Systems Research Division. Research to be conducted with the equipment, however, was planned by other branches.
Of the several elements of which a flight simulator was composed, the most difficult to develop, and most costly, was the motion generator. Owing to development difficulties and costs, the motion generator was omitted from early simulators; in fact, it was not always felt to be needed. In 1957-1958, Ames built the pitch-roll chair, a relatively crude device which provided motions about either the pitch or the roll axis. In 1960 this device was improved somewhat to allow, in flight-simulation exercises, any combination of two angular accelerations to be impressed on the pilot. The motions were produced by an amplidyne-controlled, 10-horsepower, electric motor. Two other devices for generating angular motion, one in which a large sphere was freely floated on an air bearing, were built but were not especially successful.
Harry Goett was the main driving force in getting Ames started in the flight-simulator business; when he departed for Goddard, Bill Harper car-....
....-ried on the movement with equal or greater vigor and with the effective support of George Rathert. It was, however, under Goett's direction that the pitch-roll chair was built and it was also owing to his persistent efforts that action was initiated in 1959 on the construction of what was called the "five-degrees-of-freedom motion simulator." This simulator incorporated a centrifuge of 30-foot radius. The simulated cockpit, located in a hooded cab at the end of the centrifuge arm, was driven by motors, as required by the simulation, about each of its three axes (pitch, roll, and yaw). The cab was also driven through a limited range of motion along the vertical axis and of course was driven by the centrifuge arm along a curved path of fixed radius in the horizontal plane. Thus the motions that could be simulated in the cab were three angular motions, one translational motion, and a curvilinear combination of the remaining two translational motions. The curvilinear motions, and associated accelerations, were, of course, fairly representative of airplane flight.
The motion simulation achieved by the new facility was quite good except that the rates of motion were limited by power, the range of motion was limited by structure, and the accuracy of movement was limited by precision of the controls. To have greatly reduced any of these weaknesses would have cost much more money than was available to Goett for this project. The five-degrees-of-freedom simulator was built largely of spare parts scrounged from all possible sources, and the fact that a successful device of such complexity could be built in this manner was in no small way attributable to the ingenuity of Sam Davidsen and others of the Engineering Services Division. The simulator was placed in operation early in 1961.
In the design of flight simulators, an interesting substitute had been developed for the costly and complicated motion generator. This arrange-....
 ....-ment made use of optical trickery to give the pilot the impression that he was moving while in actuality he was at rest. Such a scheme was employed in a landing-approach simulator built at Ames in 1961-1962. The simulator had a stationary transport-airplane-type cockpit incorporating more or less conventional controls and instruments. Apparent motion was provided by a commercially developed device known as the Dalto Visual Simulator. With it, a TV picture of a model moving-belt runway was projected on a screen in front of the windshield. The image thus presented gave the impression of an actual landing situation in which the attitude, elevation, and approach speed of the airplane were indicated. The landing-approach simulator was the usual closed loop consisting of pilot, controls, programed analog computer, motion generator, and cockpit instruments except that in this case the generated motion, controlled by the computer, was applied to the TV camera rather than to the cabin itself. The pilot was thus visually able to go through a landing maneuver with any airplane for which the computer had been programed. All six degrees of motion were simulated in the picture.
Another unusual, but useful, flight simulator built at Ames in 1961 was the "height control test apparatus." This device, which was attached to an exterior wall of the 40- by 80-foot tunnel building, was designed to simulate the vertical motions of an airplane, helicopter, or V/STOL aircraft. The device consisted of a cab, simulating a two-man cockpit, which by means of a motor-driven winch was moved vertically through distances of up to 100 feet at speeds as high as 22 feet per second and accelerations as high as ±1.5g. Arrangements were made whereby a TV monitor could be used to present an artificial landing scene in lieu of the real view of an open field. The height control test apparatus, which cost about $170,000, was put into use in 1962.
In none of the flight simulators built so far had motion in each of the six degrees of freedom been independently provided. In the five-degrees-of-freedom simulator, for example, the translational motions along the two axes in the horizontal plane were not independent and the motion in the vertical direction was limited to only ± 2 feet. What was really needed, Ames engineers felt, and this particularly for V/STOL work, was a truly six-degrees-of-freedom simulator that would provide a reasonably large range, say ± 10 feet, of translational motion along each axis. Such a simulator would obviously be rather large and expensive; but Bill Harper, feeling that the need was urgent, applied enough pressure to get the project under way in 1962. It would be ready for use in 1963.
The use of digital electronic computers for theoretical computations and data workup had become so extensive as to require a separate building for that purpose. A proposal for the construction of such a building, at a cost of about $2.5 million, was approved in 1959. The approved facility, named the "data reduction building," was constructed in 1960-1961 and occupied early in 1962.
In 1961 the Center's IBM 7040 was replaced by an IBM 7090 (later modified to 7094), and during the same year a Honeywell H 800 machine was leased. The H 800 had hard-wire connections to the 6- by 6-foot, the 14-foot, and the Unitary wind tunnels and was used exclusively for data workup. With the procurement of the H 800, the Electrodata machines were retired.
The use of electronic computers for administrative work at the Center was increasing steadily, and in 1962 an IBM 1401 machine was leased to handle this load. Additionally, the IBM 7094 was used for certain administrative tasks.