Aeronautics to Astronautics: NACA Research

(1952 - 1957)

LITTLE known outside the military services and the aircraft industry, the National Advisory Committee for Aeronautics by the early 1950s had far outgrown its name and could look back on nearly four decades filled with landmark contributions to military and civilian aeronautics. NACA had matured much beyond its original "advisory" capacity, had established three national laboratories, and had become perhaps the world's foremost aeronautical research organization. Drag-reducing engine cowlings, wing fillets, retractable landing gear, thin swept wings, and new fuselage shapes for supersonic aircraft - these were only a few of the numerous innovations leading to improved airplane performance that were wholly or partially attributable to the agency. NACA had pioneered in institutionalized team research - "big science," as opposed to the "little science" of individual researchers working alone or in small academic groups - and over the years such activity had paid off handsomely for the Nation.¹ NACA's relative importance in the totality of American aeronautics had declined after the Second World with the enormous increase in military research and development programs, but NACA did not exaggerate when it asserted that practically every airplane aloft reflected some aspect of its research achievements.

The contributions of NACA in aeronautics were spectacular, but regarding the inchoate discipline of astronautics, especially rocket propulsion research, the agency, like the rest of the country, was skeptical, conservative, reticent. The prevailing prewar attitude within NACA toward rocket technology was expressed in 1940 by Jerome C. Hunsaker, then a member and later chairman of NACA's Main Committee. Discussing an Army Air Corps contract with the California Institute of Technology for rocket research in relation to current NACA work on the deicing of aircraft windshields, Hunsaker said to Theodore von Kármán CalTech, "You can have the Buck Rogers job."²

In the early postwar years the leaders of NACA viewed rocket experimentation, such as the program beginning in 1945 at the Pilotless Aircraft Research Station, on Wallops Island, Virginia, as essentially a tool for aerodynamics research furthering the progress of supersonic flight within the atmosphere. NACA's annual report for 1948, for example, mentioned the heating rates generated on the noses of the V-2s then being fired at White Sands, but discussed the problem of structural heating only in the context of aircraft.³

At the request of the military services, the Langley, Lewis, and Ames laboratories did study the theoretical performance of missiles, the operation of rocket engines, the composition of rocket fuels, and automatic control arrangements for supersonic guided missiles and aircraft. But such research accounted for only a small percentage of the total NACA workload and budgetary allotments. The annual budget cuts suffered by NACA, beginning in 1949 and reaching a high point in 1954 when the agency received only a little more than half its request, perhaps intensified the scientific conservatism of the NACA leaders, while the Korean War once again shifted most NACA laboratory work to the "cleaning up" of military aircraft.⁴ It was in this climate of declining support for flight research in 1953 that NACA Director Hugh L. Dryden, who less than ten years later would be helping manage a manned lunar-landing program, wrote, "I am reasonably sure that travel to the moon will not occur in my lifetime ...."⁵

NACA Moves Toward Space

In the early 1950s, however, as a full-fledged program to develop large ballistic missiles got underway and as the rocket research airplanes reached higher into the stratosphere, NACA began to consider the prospect of space flight and what contributions the organization could make in this new area of inquiry. On June 24, 1952, the Committee on Aerodynamics, the most influential of NACA's various technical committees, met at Wallops Island. Toward the end of the meeting, committee member Robert J. Woods, the highly respected designer of "X" aircraft for the Bell Aircraft Corporation, suggested that since various groups and agencies were considering proposals for sending manned and unmanned vehicles into the upper atmosphere, NACA should set up a study group on "space flight and associated problems." To Woods, NACA was the logical agency to conduct research in spacecraft stability and control; such work would be a proper extension of current NACA activity. After some discussion the other members of the committee approved Woods' suggestion. They formally resolved that NACA should intensify its research on flight at altitudes between 12 and 50 miles and at speeds of mach 4 through 10, and "devote a modest effort to problems associated with unmanned and manned flight at altitudes from 50 miles to infinity and at speeds from Mach number 10 to the velocity of escape from the earth's gravity." On July 14 the NACA Executive Committee, the governing body of NACA, composed of practically all the members of the Main Committee, approved a slightly revised version of this resolution.⁶

Less than a month after the action of the Executive Committee, Henry J. E. Reid, Director of the Langley Aeronautical Laboratory, appointed Clinton E. Brown, Charles H. Zimmerman, and William J. O'Sullivan, aeronautical engineers at the Virginia center, to work up a thorough proposal for research in upper-atmospheric and space flight. Specifically the Langley engineers were to suggest a suitable manned vehicle on which construction could be initiated within two years. Their proposal was to be reviewed by a board composed of representatives from the three NACA laboratories and NACA's High Speed Flight Station at Edwards Air Force Base, California.⁷

Throughout the next year and a half, the Langley study group, engineers at Ames and the flight station, and the review board worked on a plan for the new research instrument. There was wide divergence of opinion as to what should be the nature and objectives of the vehicle; some parties were even skeptical about the wisdom of any space-directed research. Reid, John Stack, and others at Langley favored modifying the X-2 research airplane, then under development by Bell Aircraft, to make it a device for manned flight above 12 miles.⁸ Smith J. DeFrance, one of the early Langley engineers who had become Director of the Ames Aeronautical Laboratory when it opened in 1941, originally opposed Woods' idea for a study group on space flight because "it appears to verge on the developmental, and there is a question as to its importance. There are many more pressing and more realistic problems to be met and solved in the next ten years." DeFrance had concluded in the spring of 1952 that "a study group of any size is not warranted."⁹

In July 1954, however, representatives of NACA disclosed to the Air Force and the Navy their conclusions regarding the feasibility of an entirely new rocket-powered research airplane and suggested a tripartite program for the manned exploration of the upper atmosphere. NACA's views were based mainly on the findings and proposals of the Langley study group, which had been working on the problem since 1952 and had made a more detailed presentation than research teams from Ames and the High Speed Flight Station. NACA envisioned an aircraft that would fly as high as 50 miles and whose speed would reach perhaps mach 7 (approximately 5,000 miles per hour). Such a craft would be especially valuable for studying the critical problems of aerodynamic heating, stability, and control at high altitudes and speeds. Data gathered on its flights "would contribute both to air-breathing supersonic aircraft … and to long-range high altitude rocket-propelled vehicles operating at higher Mach numbers." Realizing that the temperatures generated on its return into the heavier atmosphere would be greater than on any previous airplane, NACA suggested as a structural metal Inconel-X, a new nickel-chrome alloy "capable of rapid heating to high temperatures (1,200°F) without the development of high thermal stresses, or thermal buckling, and without appreciable loss of strength or stiffness."¹⁰

This long-range plan was shortly accepted by the Air Force and the Navy Bureau of Aeronautics and put into motion as the "X-15 project." In December 1954, NACA, the Air Force, and the Navy agreed to proceed with the project under operating arrangements roughly similar to the previous "X" aircraft ventures. The Air Force had responsibility for finding a contractor and supervising design and construction; both the Air Force and the Navy would provide financial support; and NACA would act as technical director.¹¹

As prime contractor for the X-15, the Air Force picked North American Aviation of Los Angeles. The performance specifications of the X-15 called for a rocket engine consuming anhydrous ammonia and liquid oxygen and providing some 57,000 pounds of thrust for as long as six minutes. This powerplant would be four times as big as that of the X-2. A highly sensitive flight-data system, thick upper and lower vertical stabilizers for aerodynamic control, small reaction jets burning hydrogen peroxide for control in the near-vacuum of the upper atmosphere, and a new structural material - these were some of the novel characteristics of the stub-winged craft.¹²

The X-15 would not fulfill its original design objectives until 1962, long after NACA had become NASA and in the same year that Project Mercury achieved its basic goals. Even so, the X-15 was by far the most ambitious, expensive, and publicized research undertaking in which NACA ever participated. Its eventual success stemmed largely from the imagination and ingenuity of the NACA engineers who had started planning for an advanced aerodynamic vehicle in 1952.

In 1954, the year of Major Arthur Murray's climb to about 17 miles in the X-1A, the idea of manned rocket flight to an altitude of 50 miles seemed exceedingly visionary. Most people in NACA, the military, the aircraft industry, and elsewhere assumed that over the years vehicles with substantial lift/drag ratios would evolve to higher and higher speeds and altitudes until, by skipping in and out of the atmosphere like a flat rock across the surface of a pond, they could fly around the world. Even then, however, there were those within NACA who took the Executive Committee's mandate for "research in space flight and associated problems" literally and who felt that the X-15 concept did not go far enough. They looked to the second part of the resolution adopted by the Committee on Aerodynamics and approved by the Executive Committee, which sanctioned "a modest effort" on the "problems associated with flight at altitudes from 50 miles to infinity and at speeds from Mach number 10 to the velocity of escape from the earth's gravity."

Some of the most "far out" aeronautical engineers working for NACA in the early fifties were employed at the Ames laboratory. As early as the summer of 1952, Ames engineers, experimenting at the supersonic free-flight, 10-inch-by-14-inch, and 6-inch-by-6-inch wind tunnels at the California site, had examined the aerodynamic problems of five kinds of space vehicles - glide, skip, ballistic, satellite, and interplanetary. They knew that the aerodynamic forces acting on a vehicle above 50 miles were relatively minor, as were problems of stability and control at such altitudes. They concluded, however, that a space vehicle should probably be controllable at lower altitudes, although it "may not be optimum from the point of view of simplicity, etc...."¹³

Reentry: Aerodynamics to Thermodynamics

The Ames study had been specifically requested by NACA Headquarters, which in its initial prospectus on the new research airplane project had identified stability and control in high-speed, high-altitude flight as one of two areas needing much additional research. The other and far more critical area was aerodynamic heating, which becomes acute as an object knifes into the atmosphere from the airless environment of space and collides with atmospheric molecules of ever-increasing density. For several years NACA researchers had been studying aerodynamic heating, which begins to be troublesome at about twice sonic speed. The X-15 program was established largely to return data on heating generated up to mach 7. But such investigations of thermal stress hardly approached the heating problem faced by the military services and the missile industry in their efforts to produce a durable warhead for an intercontinental missile. In a typical ICBM flight with a peak altitude of 900 miles and a range of 6,500 miles, the stagnation temperature in the shock wave at the front of the nose cone could reach 12,000 degrees F. This is some 2,000 degrees hotter than the surface of the Sun and 10 times the maximum surface temperature that was calculated for an X-15 trajectory.¹⁴ Of the myriad puzzles involved in designing, building, and flying the Atlas, the first American ICBM, the most difficult and most expensive to solve was reentry heating. The popular term "thermal barrier" to describe the reentry problem was coined as an analogy to the "sonic barrier" of the mid-1940s, although research in the fifties would reveal that the problem could have been described more accurately as a "thermal thicket."

During June 1952, in the same summer that NACA had decided to move toward space flight research and had proposed an advanced research aircraft, one of the scientist-engineers at Ames had made the first real breakthrough in the search for a way to surmount the thermal barrier. He was Harry Julian Allen, a senior aeronautical engineer at Ames and chief of the High-Speed Research Division since 1945. The burly Allen, who signs his technical papers "H. Julian" but who is known familiarly as "Harvey," was 42 years old in 1952 and looked more like a football coach than a scientist. Holder of a bachelor of arts degree in engineering from Stanford University, Allen in 1935 had left the Stanford Guggenheim Aeronautical Laboratory, where he had received the degree of aeronautical engineer, to join the NACA staff at the Langley laboratory. When Ames was opened in 1941, he went west with Smith DeFrance and others from Langley.¹⁵

At Ames, Allen had invented a technique of firing a gun-launched model upstream through a supersonic wind tunnel to study aerodynamic behavior at high mach numbers. This notion led to the construction of the Ames supersonic free-flight wind tunnel, opened in 1949. The tunnel had a test section 18 feet long, one foot wide, and two feet high. By forcing a draft through the tunnel at a speed of about mach 3 and by firing a model projectile upstream at a velocity of 8,000 feet per second, the Ames researchers could simulate a mach number of about 15. Schlieren cameras set up at seven stations along the test section, three on the side and four on the top, made shadowgraphs to show airflow characteristics over the model and thus determine the aerodynamic forces experienced. During the 1950s the facility, constructed at an original cost of only about $20,000, was to prove one of NACA's most valuable tools for hypersonic investigation.¹⁶

As a member of one of the panels of the Department of Defense Research and Development Board, a group charged with supervising weapons research, Allen was intimately familiar with the payload protection dilemma confronting the Air Force and Convair, the prime contractor for the difficult Atlas project.¹⁷ In their designs the Convair engineers had already provided that at the peak of the Atlas' trajectory, its nose, containing a nuclear warhead, would separate from the sustainer rocket and fall freely toward its target. These exponents of the ICBM knew that without adequate thermal protection the nuclear payload would burn up during its descent through the atmosphere.

Fifty years of progress in aeronautics had produced more and more slender and streamlined aircraft shapes, the objective being to reduce aerodynamic drag and increase speed. In approaching the Atlas reentry enigma, the Convair group drew from the huge reservoir of knowledge accumulated over the years by aerodynamicists and structures experts dealing with airplanes, rockets, and air-breathing missiles. The men at Convair fed their data into a digital computer, which was supposed to help them calculate the optimum design for structural strength, resistance to heat, and free-flight stability in the separable nose section of a long-range rocket. The computer indicated that a long, needle-nosed configuration for the reentry body, similar to that of the rocket research airplanes, would be best for the ICBM. But tests of this configuration, using metal models in the supersonic wind tunnel at Ames and in rocket launches at Wallops Island, showed that so much heat would be transferred to the vehicle that the warhead would shortly vaporize as it plunged through the atmosphere. No protection system known at that time could prevent its destruction by aerodynamic heating.¹⁸

This disclosure evoked another spate of predictions that an intercontinental military rocket would not be feasible for many years. And while relatively few people were thinking seriously about manned space flight in the early fifties, those who were also understood that something radical would have to be done on the problem of reentry before it would be practicable to send a man into space and recover him.

The man who did something radical was Allen. As Allen put it, the Convair engineers "cut off their computer too soon." He took the sharp-nosed Atlas reentry shape and began making mathematical calculations, using only a pad and pencil. Eventually he reached a conclusion that seemingly contradicted all the years of aeronautical research and streamlined aircraft design. For Allen's analysis showed that the best way to cut down reentry heating was to discard a great deal of one's thinking about orthodox aerodynamics and deliberately design a vehicle that was the opposite of streamlined. "Half the heat generated by friction was going into the missiles," recalled Allen. "I reasoned we had to deflect the heat into the air and let it dissipate. Therefore streamlined shapes were the worst possible; they had to be blunt." The Ames researcher determined that the amount of heat absorbed by an object descending into the atmosphere depended on the ratio between pressure drag and viscous or frictional drag. The designer of a reentry body, by shaping the body bluntly, could alter pressure drag and thus throw off much of the heat into the surrounding air. When the bluff body collided with stratospheric pressures at reentry speeds, it would produce a "strong bow shockwave" in front of, and thus detached from, the nose. The shock wave, the air itself, would absorb much of the kinetic energy transformed into heat as the object entered the atmosphere.¹⁹

Allen personally submitted his findings to select persons in the missile industry in September 1952. A secret NACA report memorandum embodying his conclusions on the blunt-nose design, coauthored by Alfred J. Eggers of Ames, went out to industrial firms and the military the next spring. The report bore the date April 28, 1953, but six years passed before the paper was declassified and published in the annual report of NACA.²⁰

For his conception of the blunt-body configuration, Allen received the NACA Distinguished Service Medal in 1957. The award brought sharp criticism from H. H. Nininger, director of the American Meteorite Museum at Sedona, Arizona, who asserted that he had first proposed the blunt nose for reentry vehicles. In August 1952, Nininger, a recognized authority on meteorites, had suggested to the Ames laboratory that a blunt shape appeared promising for missile warheads. Nininger based his conclusion on his studies of tektites and meteorites, contending that the melting process experienced by a meteorite during its descent through the aerodynamic atmosphere furnished a lubricant enabling the object to overcome air resistance. Nininger's letter evidently came to Ames some weeks after Allen, assisted by Eggers, had completed his calculations on the relationship between warhead shape and heat convection. At any rate, what Allen wanted to do was exactly the reverse of Nininger's suggestion: deliberately to shape a reentry body bluntly in order to increase air resistance and dissipate a greater amount of the heat produced by the object into the atmosphere.²¹

Allen's high-drag, blunt-nose principle was of enormous interest and benefit to the missile designers. It led directly to the Mark I and Mark II nose cones developed by the General Electric Company for the Atlas and later for the Thor. Years after the discovery, James H. Doolittle, chairman of NACA's Main Committee, pointed out that "every U.S. ballistic missile warhead is designed in accordance with his once radical precept."²² In 1952 the problems of the missilemen were not of immediate concern to designers of manned flight systems, not even to those drawing up plans for the X-15, which would encounter a greater heating load than any previous airplane. Yet Allen's presentation of a new way to minimize the aerodynamic heating of reentry not only made possible an ICBM within a few years but "marked the potential beginning of manned space flight, with all of its attendant new structures and materials problems."²³

The blunt-nose concept was just that - a concept. Succeeding years would see much experimentation with spheres, cylinders, blunted ogives, and even concave shapes at the supersonic free-flight tunnel, ballistic ranges, and various other facilities at Ames, at the 11-inch hypersonic tunnel at Langley, and at the Pilotless Aircraft Research Station on Wallops Island.²⁴ As aerodynamicists began thinking about space flight they would propose a variety of configurations for potential manned space vehicles, although all of the designs would feature some degree of bluntness. Finally, blunting a reentry body furnished only part of the solution to the heating problem. Allen's calculations presupposed that some kind of new thermal protection material would be used for the structure of a high-drag body. In 1952, aircraft designers and structures engineers were working mainly with aluminum, magnesium, and titanium, and were giving some attention to such heat-resistant alloys as Monel K, a nickel-and-steel metal used in the X-2, and Inconel-X, the basic alloy for the X-15.²⁵ But it would take much "hotter" materials to protect the payloads of the intercontinental and intermediate-range ballistic missiles - the Atlas, the Thor, the Jupiter, and later the Titan. Far more materials research was needed before the recovery of a manned spacecraft would be practicable.

Early in 1956, the Army Ballistic Missile Agency at Huntsville, Alabama, modified some of its medium-range Redstones in order to extend the studies of reentry thermodynamics that the Army had pursued at Redstone Arsenal since 1953. As modified, the Redstone became a multistage vehicle, which Wernher von Braun and his colleagues called the "Jupiter C" (for Composite Reentry Test Vehicle). Meanwhile the Air Force conducted its own investigations of reentry in conjunction with its nose-cone contractors, General Electric and the Avco Manufacturing Corporation, using a special multistage test rocket called the X-17, manufactured by the Lockheed Aircraft Corporation.²⁶

Two principal techniques for protecting the interior of the nose cone offered themselves - "heat sink" and "ablation." The heat sink approach involved using a highly conductive metal such as copper or beryllium to absorb the reentry heat, thus storing it and providing a mass sufficient to keep the metal from melting. The major drawback of a heat sink was its heaviness, especially one made of copper. In the ablation method the nose cone was covered with some ceramic material, such as fiber glass, which vaporized or "ablated" during the period of reentry heating. The vaporizing of the material, the conversion of a solid into a gas, dissipated or carried away the heat. Thus the essence of the ablation technique was deliberately burning part of the exterior surface of the reentry body, but designing the body so that the surface would not burn through completely.²⁷

Apparently no consensus existed among students of the reentry problem by late 1957. The "first generation" ICBM nose cones produced by General Electric, the Mark I and Mark II, were blunt, heavy copper heat sinks, and the Air Force had decided to use the Mark II on its Thor intermediate-range missile. But the Air Force's full-scale tests of the lighter, more sophisticated, but more difficult and less tidy ablation process had not begun yet. Meanwhile, the Army and the Vitro Corporation, using the exhaust of liquid rocket motors as a heat source and the hybrid Redstone in reentry simulations, demonstrated to their own satisfaction the practicability of consuming part of the structural material during its use, the principle of ablation. The Army's Jupiter-C shot of August 8, 1957, carrying a scale model Jupiter nose cone to an altitude of 600 miles and a range of 1,200 miles, supposedly "proved the feasibility of the ablative-type nose cone" and "fulfilled the mission of the reentry test program."²⁸ Yet the Ballistic Missile Agency engineers at Redstone Arsenal were working only on the intermediate-range Jupiter, not on an ICBM. The question of whether an Atlas warhead or a manned reentry vehicle could best be protected by the heat-sink or ablation method, or by either, remained undetermined. Much time and effort would be expended before the Army's claims for ablation would be fully verified and accepted.

NACA's official role in this accelerated program of materials research was that of tester and verifier. Even so, the NACA experimenters greatly enlarged their knowledge of thermodynamics, became well grounded in the new technology of thermal protection, and prepared themselves to cope with the heating loads to be encountered in manned space flight.

At the request of the Air Force, the Army, and also the Navy (which was involved with the Polaris after 1956), NACA devoted an increasing portion of its facilities and technical staff to tests of such metals as copper, tungsten, molybdenum, and later beryllium for heat sinks, and of ablating materials like teflon, nylon, and fiber glass. During 1955-1956 the installation of several kinds of high-temperature jets at the Langley and Lewis laboratories greatly aided NACA thermodynamics research. These included, at Langley, an acid-ammonia rocket jet providing a maximum temperature of 4,100°F and a gas stream velocity of 7,000 feet per second, an ethylene-air jet yielding temperatures up to 3,500°F, and a pebble-bed heater, wherein a stream of hot air was passed through a bed of incandescent ceramic spheres. Both Langley and Lewis had electric arc jet facilities, in which a high-intensity arc was used to give energy to compressed air and raise air pressure and temperatures. The hot, high-pressure air then shot through a nozzle to produce a stream temperature of about 12,000°F. NACA investigators used these high-temperature jets and other research tools, including the 11-inch hypersonic tunnel at Langley, to gather data eventually reinforcing the Army's contention that ablation was the most effective thermal protection method.²⁹

Meanwhile Maxime A. Faget, Paul E. Purser, and other members of the Langley Pilotless Aircraft Research Division, working under the supervision of Robert R. Gilruth, used multistage, solid-propellant rockets for studying heat transfer on variations of Allen's basic blunt heatshield configuration. Robert O. Piland, for example, put together the first multistage vehicle to attain mach 10. Faget served as a regular NACA member and Purser was an alternate member of a Department of Defense panel called the Polaris Task Group, set up to give advice on the development of the Navy's intermediate-range, solid-fueled Polaris, which was to be launched from submerged submarines. NACA worked with the Atomic Energy Commission and the Lockheed Aircraft Corporation, prime contractor for the Polaris, in developing the heat-sink nose cone used on the early versions of the sea-based missile.³⁰

Although there were some 30 different wind tunnels at Langley, the members of the Pilotless Aircraft Research Division (PARD) firmly believed in the superiority of their rocket-launch methods for acquiring information on heating loads and heat transfer, heat-resistant materials, and the aerodynamic behavior of bodies entering the atmosphere. As Faget said, "The PARD story shows how engineering experimentalists may triumph over theoreticians with preconceptions. Our rockets measured heat transfer that the tunnels couldn't touch at that time." Joseph A. Shortal, chief of PARD since 1951, recalled, "PARD made us more than aeronautical engineers and aerodynamicists. We became truly an astronautically oriented research and development team out at Wallops."³¹

The Ames experimenters, on the other hand, were just as firmly convinced that their wind tunnels and ballistic ranges represented the simplest, most economical, and most reliable tools for hypersonic research. To the Ames group, rocket shots were troublesome and expensive, and rocket telemetry was unreliable. As one Ames engineer put it, "You might get a lot of data but since you didn't control the experiment you didn't know exactly what it meant."³²

The Ames devotion to laboratory techniques, the determination to do more and more in heating and materials research without resorting to rockets, furnished the impetus for a new test instrument devised by Alfred J. Eggers, Jr., in the mid-fifties. Eggers, born in 1922 in Omaha, had joined the research staff at Ames in the fall of 1944, after completing his bachelor of arts degree at the University of Omaha. He pursued graduate studies at Stanford University in nearby Palo Alto, where he received a Master of Science degree in aeronautical engineering in 1949 and a Ph.D. in 1956.³³ For years Eggers had worked with Allen and others at Ames on the aerodynamic and thermodynamic problems of hypervelocity flight, and as a conceptualizer at the California center he came to be regarded as second only to the originator of the blunt-nose reentry principle.

Eggers assumed that the major heating loads of reentry would be encountered within an altitude interval of 100,000 feet. So he designed a straight, trumpet-shaped supersonic nozzle with a maximum diameter of 20 inches and a length of 20 feet, which in terms of the model scale used was equivalent to 100,000 feet of thickening atmosphere. A hypervelocity gas gun launched a scale model upstream through the nozzle to a settling chamber. While in free flight through the nozzle to the chamber, the model passed through ever-denser air, thus closely approximating the flight history of a long-range ballistic missile. Since the apparatus simulated both motion and heating experiences, Eggers called the combination of hypervelocity gun and supersonic nozzle "an atmosphere entry simulator."³⁴

Eggers calculated that using a model only .36 inch in diameter and weighing .005 pound, he could simulate the aerodynamic heating generated by an object three feet in diameter, weighing 5,000 pounds, and having a range of 4,000 miles. "In the simplest test," he said, "the simulator could provide with one photograph of a model rather substantial evidence as to whether or not the corresponding missile would remain essentially intact while traversing the atmosphere." The reentry research technique, proposed in 1955, went into operation during the next year. Construction of a larger version began in 1958. Eggers' atmosphere entry simulator proved especially useful in materials research at Ames. Like the high-temperature jets at Langley and Lewis, the rocket tests at Wallops Island, the Army's Jupiter-C shots from Cape Canaveral, and other experimental methods, it yielded data that later pointed toward ablation as the best method for protecting the interior of reentry bodies.³⁵

Although the official focus of the NACA materials test program remained on missile warhead development, such activity was an obvious prerequisite to manned space flight. And the experience of men like Gilruth, Faget, Purser, and Shortal in the years before the Sputniks had a direct influence on their plans for shielding a human rider from the heat of atmospheric friction. Meanwhile other NACA engineers, especially at Langley and at the High Speed Flight Station, were working closely with the Navy, the Air Force, and North American Aviation on the X-15 project. At Cleveland, Lewis propulsion specialists were studying rocket powerplants and fuels as well as cooperating with Langley and Flight Station representatives in designing, operating and studying reaction control systems for hypersonic aircraft and reentry vehicles.

A Moon for a Man

Others in NACA, sensing the potential for manned space exploration that accompanied propulsion advances in military rocketry, began considering designs for a vehicle with which man could take his first step above the atmosphere. Early in 1954, Eggers, Julian Alien, and Stanford E. Neice of Ames put together a classic theoretical discussion of different space flight configurations in a paper entitled "A Comparative Analysis of the Performance of Long-Range Hypervelocity Vehicles." The research engineers examined the relative advantages, in terms of range and the ratio between payload and total weight, of three kinds of manned hypersonic vehicles: ballistic, a blunt non-lifting, high-drag projectile skip; and glide, the last two designs also having fairly blunt noses but possessing some lifting ability. For satellite missions all three vehicles might be booster to orbital velocity by a rocket and could then separate from the rocket and go into free flight, or orbit.

Eggers, Alien, and Neice found that the skip vehicle, which would return to Earth by performing an intricate series of progressively steeper dips into the atmosphere, would need an extremely powerful boost to circumnavigate the globe and also would encounter a prohibitively large amount of aerodynamic heating.³⁶ By contrast, the glider, although heavy, would require less boost and would keep the g forces imposed on the pilot during reentry at a quite acceptable level. Like the skip craft, the glider would provide the advantage of pilot control during the landing phase. It would radiate heat well, but since its thermodynamic load still would be high, the glider might experience dangerous interior heating during a "global" satellite) mission. So the authors suggested a high-lift glider; like the high-lift-over-drag glider, it would have a delta-wing configuration but also would feature thick, rounded sides and bottom to minimize interior heating. It would enter the atmosphere at a high angle of attack, then level off at lower altitudes to increase the lift/drag ratio.

The ballistic vehicle, the simplest approach of the three, could not be controlled aerodynamically, but its blunt shape provided superior thermal protection, and its relatively light weight gave it a longer range. If it entered the atmosphere at a low angle, deceleration forces could be kept at or below 10 g, with 5 g lasting for 1 minute and 2 g for not over 3 minutes. Therefore the three NACA researchers concluded that "the ballistic vehicle appears to be a practical man-carrying machine, provided extreme care is exercised in supporting the man during atmospheric entry."³⁷

As time passed, Eggers personally became convinced of the overall desirability of the manned satellite glider as opposed to the ballistic satellite. He revealed his preference in a modified version of the earlier paper done with Alien and Neice, which he read before the annual meeting of the American Rocket Society in San Francisco, in June 1957. Eggers was skeptical about the relatively high heating loads and the deceleration forces characteristic of ballistic reentry, even at a small entry angle. He warned that "the g's are sufficiently high to require that extreme care be given to the support of an occupant of a ballistic vehicle during atmospheric reentry," and pointed out that such an object, entering the atmosphere along a shallow trajectory so as to hold deceleration down to 7.5 g, would generate a surface temperature of at least 2,500 degrees F. Thus, in Eggers' judgment, "the glide vehicle is generally better suited than the ballistic vehicle for manned flight at hypersonic velocities."³⁸

Eggers realized that his glider design, if actually built, would be too heavy for the military rockets then under development. At the same time he remained concerned about the deceleration loads imposed on the space pilot and the heating loads on the spacecraft structure. He also saw the difficulty of recovering a ballistic satellite, which since it was noncontrollable in the atmosphere, would have to land somewhere in a target area of several thousand square miles. As a consequence of these apprehensions, during the last half of 1957 he sketched a semiballistic device for manned orbital flight, blunt but having a certain amount of aerodynamic lift, with a nearly flat top and a round, deep bottom for heat protection. This design, which Eggers called the "M-1," fell about halfway between the high-lift glider and the ballistic vehicle discussed in his 1954 NACA study with Allen and Neice. About 10 feet wide and nearly seven feet long, the M-1 from above looked like an isosceles triangle rounded at its apex³⁹ A more graphic description was offered by Paul Purser, who called it a "¼ egg lifting shape." ⁴⁰40 The M-1's limited amount of lift would give it about 200 miles of lateral maneuverability during its descent through the atmosphere and about 800 miles of longitudinal discretion over its landing point. Eggers' calculations indicated that skillful piloting could keep reentry deceleration at about 2 g. 41⁴¹

Air Force Provides a Need

The work of Eggers and others on designs for man-carrying space vehicles had been stimulated not only by general progress in long-range rocketry but also by the growing interest of the Air Force in manned space flight. Eggers knew that ever since the war the Air Force, through the Rand Corporation, had been considering the military potential of space technology, and that since early 1956 the service had been proceeding cautiously with contract feasibility studies of manned satellites.

The impetus for these feasibility studies came from a staff meeting at the headquarters of the Air Research and Development Command ARDC at Baltimore, on February 15, 1956. During the course of the meeting, General Thomas S. Power, Commander of ARDC, expressed-impatience with the failure of his "idea men" to propose any advanced flight systems that could be undertaken after the X-15. Work should begin now, he declared, on two or three separate approaches beyond the X-15, including a vehicle that would operate outside the atmosphere without wings. He suggested that a manned ballistic rocket might be "eventually capable of useful intercontinental military and commercial transport and cargo operation." But the main benefit of having an advanced research project underway, Power pointed out, was that the Air Force could more easily acquire funds for the "general technical work needed."⁴²

Thus prodded into action, Power's staff quickly proposed two separate research projects. The first called for a "Manned Glide Rocket Research System" - a rocket-launched glider that would operate initially at an altitude of about 400,000 feet and a speed of mach 21. The other, termed "Manned Ballistic Rocket Research System," would be a separable manned nose cone, or capsule, the final stage of an ICBM. Such a vehicle could lead to the "quick reaction delivery of high priority logistics to any place on Earth," as suggested by Power, or to a manned satellite. Power's staff argued that the manned ballistic concept offered the greater promise, because the solution to the outstanding technical problems, the most critical of which was aerodynamic heating, would result from current ICBM research and development; because existing ICBMs would furnish the booster system, so that efforts could be concentrated on the capsule; and because the ballistic vehicle possibly could be developed by 1960. Either program, however, should be pushed rapidly so that the Air Force could protect its own interests in the field of space flight!⁴³

In March 1956, ARDC established two research projects, one for the glide rocket system, the other, known as Task 27544, for the manned ballistic capsule. ARDC planners shortly held briefings on the two proposed systems for its missile-oriented Western Development Division, in California, and for its pilot-oriented Wright Air Development Center, in Ohio. Other briefings were held for NACA representatives and for aircraft and missile contractors. Then, in October, Major George D. Colchagoff of Power's staff described the basic aspects of the two advanced systems to a classified session of the American Rocket Society's annual meeting in Los Angeles.⁴⁴

Since the Weapons Systems Plans Office of ARDC Headquarters never received the $200,000 it had requested for its own feasibility studies, the command had to content itself with encouraging privately financed contractor research.⁴⁵ In particular Avco, then trying to develop serviceable nose cones for the Thor and Atlas missiles, was urged to study the manned ballistic capsule. In November 1956, Avco submitted to the Research and Development Command a preliminary study embodying its conclusions on the ballistic approach to manned space flight. ARDC still was short of funds, so Avco and other corporations continued to use their own money for further investigations.⁴⁶

While ARDC promoted these systems studies and sponsored extensive research in human factors at the School of Aviation Medicine in Texas, at the Aeromedical Field Laboratory in New Mexico, and at the Aeromedical Laboratory in Ohio, it also sought to gain acceptance for its ideas within the Air Force organizational structure. On July 29, 1957, the Ad Hoc Committee of the Air Force Scientific Advisory Board, meeting at the Rand Corporation's offices in Santa Monica, California, heard presentations from the Ballistic Missile Division on ballistic missiles for Earth-orbital and lunar flights, and from ARDC Headquarters on the two advanced flight systems then under study. Brigadier General Don D. Flickinger, ARDC's Director of Human Factors, stated that from a medical standpoint sufficient knowledge and expertise already existed to support a manned space venture.⁴⁷

Although the industrial firms investigated mainly the manned ballistic capsule, NACA, following the traditional approach of building up to higher and higher flight regimes, centered its efforts on the glide-rocket concept for most of 1957. Since late the previous year, when NACA had agreed in principle to an ARDC invitation to cooperate on the Manned Glide Rocket Research System, as they were doing for the X-15, small teams of engineers at the Langley, Lewis, and Ames laboratories had carried on feasibility and design studies.⁴⁸ In January 1957 the Ames group reported its conclusions on a new rocket-powered vehicle for "efficient hypersonic flight," featuring a flat-top, round-bottom configuration. Interestingly enough, the Ames document contained as an appendix a minority report written by Langley aerodynamicists mostly from the Flight Research, Instrument Research, and Pilotless Aircraft Research Divisions - recommending that a nonlifting spherical capsule be considered for global flight before a glide rocket.⁴⁹ "The appendix was widely read and discussed at Langley at the time" recalled Hartley A. Soulé, a Langley senior engineer, "but there was little interes expressed in work on the proposal." He continued:

…aside from the environment that limited the NACA mission to terrestrial transportation, the proposal was criticized on technical grounds. The report suggested that landings be made in the western half of the United States, not a very small area. The spherical shape was suggested so that the attitude would not be important during reentry. The shape was specifically criticized because the weight of material to completely shield the surface from the reentry heat would probably preclude the launching with programmed ICBM boosters. Further, the lack of [body] orientation might result in harm to the occupant during the deceleration period.⁵⁰

NACA study groups continued their investigations of manned glide rocket concepts through the spring and summer. In September 1957 a formal "Study of the Feasibility of a Hypersonic Research Airplane" appeared, bearing the imprimatur of the whole NACA but influenced primarily by Langley proponents of a raised-top, flat-bottom glider configuration.⁵¹

A few days later, on October 4, Sputnik I shot into orbit and forcibly opened the Space Age. The spectacular Russian achievement wrought a remarkable alteration in practically everyone's thinking about space exploration, especially about the need for a serious, concerted effort to achieve manned space flight. New urgency attended the opening of a long-planned NACA conference beginning October 15 at Ames, which was to bring together representatives from the various NACA laboratories in an effort to resolve the conflict in aerodynamic thinking between advocates of round and flat bottoms for the proposed hypervelocity glider. Termed the "Round Three Conference," the Ames meeting produced the fundamental concept for what would become the X-20 or Dyna-Soar for dynamic soaring project a delta-wing, flat-bottom, rocket-propelled glider capable of reaching a velocity of mach 17.5, almost 13,000 miles per hour, and a peak altitude of perhaps 75 miles.⁵²

Although they had been working mainly on the hypersonic glider, as requested by the Air Force, the research engineers of PARD, in tidewater Virginia, also had been speading more and more time thinking about how to transmute missile reentry bodies into machines for carrying man in low Earth orbit. Their advocacy, along with that of other Langley workers, of a spherical capsule early that year had indicated their growing interest in making the quantum jump from hypersonic, upper- atmospheric, lift drag flight to orbital space flight in a nonlifting vehicle. At the Round Three Conference, Faget and Purser compared notes with Eggers, perhaps the leading hypervelocity theoretician in NACA. Eggers related his own conclusions: for orbital flight the design giving the highest proportion of payload to total weight was the compact, low lift drag vehicle, having little or no wings, and embodying Allen's blunt-nose principle. He discussed the analytical studies of his semiballistic M-1, which had some lift but would, he estimated, weigh from 4,000 to 7,500 pounds. Eggers cautioned his NACA colleagues that a nonlifting, or pure ballistic, vehicle might subject the passenger to excessive deceleration forces.⁵³

Faget and Purser returned to Langley convinced that a maximum concentration of effort to achieve manned orbital flight as quickly as possible was imperative.⁵⁴ Obviously this meant that in the months ahead their research should focus on the ballistic-capsule approach to orbiting a man. Both the hypersonic glider, which called for progressing to ever higher speeds and altitudes, and Eggers' M-1, also too heavy for any existing booster system, would take too long to develop. The manned ballistic vehicle combined a maximum of simplicity and heat protection with a minimum weight and offered the best chance of getting a man into space in a hurry. Henceforth the aerodynamicists in PARD, and space enthusiasts in other units of the Langley laboratory, turned from NACA's historic preoccupation with winged, aerodynamically controllable vehicles and devoted themselves to the study of "a man in a can on an ICBM," as some in the Air Force called it.⁵⁵

After Sputnik I, the aircraft and missile corporations also stepped up their research on the ballistic capsule; throughout November and December their design studies and proposals flowed into ARDC Headquarters. The most active of the firms considering how to put a man on a missile still was Avco. On November 20, 1957, it submitted to ARDC its second and more detailed study of systems for manned space flight, entitled "Minimum Manned Satellite." The Avco document concluded that "a pure drag reentry vehicle is greatly superior in satisfying the overall system requirements," and that the best available rocket for boosting a manned satellite into an orbit about 127 miles from Earth was the Atlas. Still unproven, the Atlas was to make its first successful short-range flight (500 miles) on December 17, 1957. An Atlas-launched satellite, according to the Avco idea, would be a manned spherical capsule that would reenter the atmosphere on a stainless-steel-cloth parachute. Shaped like a shuttlecock, the parachute was supposed to brake the capsule through reentry. Then air pressure would expand the parachute to a diameter of 36 feet, and the capsule would land at a rate of 35 feet per second.

Avco requested $500,000 to cover the expense of a three-month study and the construction of a "mockup," or full-scale model, of the capsule containing some of its internal systems. But because the Ballistic Missile Division was skeptical about the drag-brake apparatus, and because ARDC was uncertain about Air Force plans in general, a contract was not awarded. Avco engineers, believing that the limiting factor in putting a man in orbit was not the capsule but the development of a reliable booster, focused on the Atlas and began holding discussions with representatives of Convair, builder of the Atlas.⁵⁶

Jockeying for Position

On October 9, only five days after Sputnik I, the Ad Hoc Committee of the Air Force Scientific Advisory Board urged the development of "second generation" ICBMs that could be used as space boosters, proposed the eventual accomplishment of manned lunar missions by the Air Force, and recommended the launching of Air Force satellites for reconnaissance, communications, and weather prediction purposes as soon as possible. A few days later, Secretary of the Air Force James H. Douglas appointed a committee of 56 academic and corporate scientists and Air Force officers, headed by the eminent but controversial nuclear physicist Edward N. Teller, to "propose a line of positive action" for the Air Force in space exploration. Not surprisingly, the Teller Committee in its report of October 28 recommended a unified space program under Air Force leadership.⁵⁷

Then, on December 10, 1957, Lieutenant General Donald L. Putt, Air Force Deputy Chief of Staff, Development, set up a "Directorate of Astronautics" for the Air Force. Brigadier General Homer A. Boushey, who sixteen years earlier had piloted the first rocket-assisted aircraft takeoff in this country, became head of the new office. The move quickly met opposition from Secretary of Defense Neil H. McElroy, who was chary about any of the services using the term "astronautics," and from William M. Holaday, newly appointed Defense Department Director of Guided Missiles, whom the New York Times quoted as charging that the Air Force wanted to "see if it can grab the limelight and establish a position." The furor within the Defense Department caused Putt to cancel the astronautics directorate on December 13, only three days after its establishment.⁵⁸

Sputnik II, the dismayingly large, dog-carrying Soviet satellite, had gone into orbit on November 3. As the mood of national confusion intensified in the last weeks of 1957, Headquarters USAF ordered the Air Research and Development Command to prepare a comprehensive "astronautics program," including estimates of funding and projected advances in space technology over the next five years. ARDC, which had been working on its own 15-year plan for Air Force research and development in astronautics, now boiled its findings down to a five-year prospectus. ARDC's report went to Headquarters USAF on December 30, and at the end of the year of the Sputniks the five-year plan was under consideration in the Pentagon.⁵⁹

In any Air Force push into astronautics, NACA presumably would play a key role as supplier of needed research data. The agency had done this for nearly four decades in aeronautics. Proceeding on this premise, Putt wrote NACA Director Dryden on January 31, 1958, formally inviting NACA's participation in a man-in-space program with the Air Force, including both the boost-glide research airplane, soon to be dubbed Dyna-Soar, and "a manned one-orbit flight in a vehicle capable only of a satellite orbit… ."⁶⁰ Dryden promptly approved NACA cooperation on the first approach, although the research agency and the Air Force would not sign their formal agreement on the subject until the following May.⁶¹ Regarding the satellite project offer, however, Dryden informed Putt that NACA was working on its own designs for a manned space capsule and would "coordinate" with the Air Force late in March, when NACA completed its studies.⁶²

Behind NACA's apparent reluctance to follow the Air Force lead into manned satellite development was a conviction, held by some people at NACA Headquarters, but mainly by administrators and engineers of the Langley and Lewis laboratories, that the agency should broaden its activities as well as its outlook. Moving into astronautics, NACA should leave behind its historic preoccupation with research and expand into systems development and flight operations - into the uncertain world of large contracts, full-scale flight operations, and public relations. NACA should, in short, assume the leadership of a new, broad-based national space program, having as one of its principal objectives to demonstrate the practicability of manned space flight.

So in the 10 months between the first Sputnik and the establishment of a manned space program under a new agency, NACA would follow a rather ambivalent course. On one hand it would continue its traditional research and consultative capacity, counseling the Air Force on space flight proposals and imparting its findings to industrial firms. But at the same time ambitious teams of engineers here and there in the NACA establishment would be preparing their organization and themselves to take a dominant role in the Nation's efforts in space.