1. Introduction



[1] In September 1944, a general and a professor met in an Air Force car parked at one end of a runway of New York's LaGuardia airport. General of the Army H. H. Arnold, chief of the Army Air Forces and on his way to a meeting in Quebec, had arranged the meeting with Professor Theodore von Karman famed aerodynamicist and jet propulsion pioneer at the California Institute of Technology. The two had first met in 1936; they had discussed auxiliary rocket thrust for bombers in 1938 and the design of a new research wind tunnel in 1939. Now Arnold wanted von Karman to come to the Pentagon to draw up a plan for aeronautical research during the next twenty years.1 Confident that the war was won, Arnold had turned to the future.


When the group of scientists von Karman had organized for the task met in January 1945, Arnold stated his feelings bluntly: "I don't think we dare muddle through the next twenty years the way we have ... the last twenty years. . . . I don't want ever again to have the United States caught the way we were this time.2 Arnold was referring to technological superiority in the air.


When Arnold and the combined chiefs of staff met with Roosevelt and Churchill in Quebec, the tide of battle in Europe was decisively in favor of the Allies. Fleets of Allied aircraft were pounding Germany's industrial capacity into rubble. Eisenhower's armies were moving towards the Rhine and some units were on German soil near Aachen. In the Pacific, MacArthur was able to step up his plans for landing on Leyte by two months. U.S. production of aircraft and training of air personnel so far exceeded the demands of war that both were cut back in the fall of 1944 to save money.3


The air supremacy of the Allied European offensive in 1944 came not from technological superiority but sheer weight of numbers and better trained crews. Between May 1940 and September 1943, the United States alone produced 128000 aircraft and 349 000 engines.4 By 1944, however, there was ample evidence that pistonengine aircraft were rapidly becoming obsolete and that future military aircraft would be jet-propelled.


From the beginning, airplanes had been powered by the piston engine-propeller combination. Jet propulsion had been examined in the early 1920s but rejected as too inefficient at the prevailing aircraft speeds of 400 kilometers per hour. By the late 1930s, however, potential airplane speeds had doubled and this, along with other technical advances, made jet propulsion more attractive. Development began in Europe during the second half of the 1930s, but little work was done in the United States on gas [2] turbine engines until 1939.* Even then, the U.S. military was lukewarm about the potential of jet aircraft.5


The two most serious disadvantages of early gas turbine engines for aircraft were their low thrust, which made long take-off rolls necessary, and high fuel consumption, which limited range. These disadvantages chilled Navy interest in gas turbines as primary propulsion systems until 1943. The Army showed greater interest in rocket propulsion for aircraft, rather than gas turbine engines. The Army became interested in rocket propulsion in 1938; in February 1941, when Arnold learned from intelligence reports that the Germans were using rocket propulsion, he asked the National Advisory Committee for Aeronautics (NACA) to study jet propulsion. The NACA, the government's aeronautical research organization, set up an advisory committee headed by 83-year-old Dr. William F. Durand, eminent aerodynamicist at Stanford University. Durand's interest in turbine machinery directed the NACA study almost entirely towards gas turbine engines. Representatives from three firms proficient in turbine machinery-Allis Chalmers, Westinghouse, and General Electric-served on the Durand committee, and their firms were given study contracts by the military services.6


Arnold visited Great Britain in the spring of 1941 and was impressed by the Whittle gas turbine engine. He arranged for General Electric to manufacture it in the United States. On 2 October 1942, the Bell P-59A, powered by a General Electric I-A gas turbine engine, became the first American jet-propelled aircraft to fly. The I-A produced so low a thrust, however, that performance was disappointing. Despite later installation of a more powerful engine, the 1-16, the P-59A did not reach the production stage. The British developed the Meteor powered by a Rolls Royce W-2B gas turbine engine and used it in World War 11, although its performance was little if any better than that of the P-59A. By 1944, General Electric had developed a much more powerful gas turbine engine, the 1-40, which was used to power the Lockheed XP80A fighter, developed by Clarence L. (Kelly) Johnson in just 143 days.7 Production began before the war ended, but the P-80 did not reach tactical units until seven months after the war ended in Europe.


In mid-1944, the Allies confirmed that the Germans were using turbojet interceptors against Allied bombers. By January 1945, a special German squadron of sixteen ME-262 turbojet fighters, armed with twenty-four 55 mm rockets, operated against Allied bomber formations with high success. In early April 1945, a German pilot, tired of the war, landed an ME-262 at an Allied airfield. Arnold questioned the pilot about its capability and arranged for shipment of the aircraft to Wright Field for evaluation.8


Robert Schlaifer, who studied the development of aircraft engines through World War II, saw the lag of jet propulsion in the United States as a lesson in the importance of avoiding delays in adopting new technology:


[3] The most serious inferiority in American aeronautical development which appeared during the Second World War was in the field of jet propulsion. Had the Germans put their jet fighters in production a year sooner, as they were technically able to do, or had the Allied campaign in Europe come a year later, the use of jet fighters by the Germans might have had a most serious effect on the course of the war.9


What about the aeronautical research laboratories of the NACA and Air Force? Why had they not led in investigating advanced forms of propulsion? They had been slow in recognizing, during the second half of the 1930s, that the time of the gas turbine engine had come. A few investigators in NACA, particularly Eastman Jacobs and Benjamin Pinkel, began to realize this and were working on the problem by 1939, but progress was slow. The Durand committee provided new stimulus, but by that time war was close. The policy of mass production of piston engines led U.S. aeronautical laboratories to concentrate on solving urgent problems arising from their production and operation. Improvements were made in aviation fuels, in engine components such as the turbosupercharger, and in numerous operating problems. The laboratories of the NACA were at the disposal of the military services for this effort, giving first priority to war-related problems, leaving little time for long-range work on advanced propulsion systems.


In spite of concentration on piston engine problems, however, NACA continued some research on jet engines and rockets. In December 1943, both the Army and Navy asked the NACA to evaluate their jet engines developed under contracts originally recommended by the Durand committee. The first test was made in the unique altitude wind tunnel at NACA's engine laboratory in May 1944, and by fall the tunnel was used exclusively for jet engine research. The same year, NACA's director of research, George Lewis, authorized the engine laboratory in Cleveland to spend $43 000 for the construction of some simple rocket test stands; and about the same time, researchers at the NACA Langley laboratory began eyeing rockets as a means of propelling experimental models to transonic and supersonic speeds for aerodynamics and controls research.10


Late in 1944, the government aeronautical laboratories felt an easing of the pressure to concentrate on ad hoc problem solving, freeing men and funds for advanced concepts. The suppression of the long-felt desire by researchers to work on advanced propulsion was accentuated by reports of German accomplishments in jet propulsion and rockets, particularly the V-2. Teams of scientists and engineers were dispatched to obtain German technical data in the wake of advancing Allied armies and to interrogate German technical specialists. Plans were made to bring a group of German rocket experts to the United States. The mood in the government propulsion laboratories was the same as that expressed by Arnold to his advisory group-to catch up and not ever fall behind again in advanced propulsion.


Parallel to NACA research on aeronautics during the war was research and development in other fields of military importance by a large group of scientists and engineers, coordinated by the Office of Scientific Research and Development (OSRD). Among the many significant contributions OSRD made was rocketry. At the time of the Pearl Harbor attack, the U.S. military did not have a single rocket in service use; [4] but by the end of the war, $1.35 billion worth of solid-propellant rockets were being produced annually, mostly for the Navy. These were short-range, armament rockets. OSRD also sponsored work on liquid-propellant rockets for assisted take-off of aircraft. Information on the German V-2 was available to OSRD by mid-1943, but there were no plans for long-range rockets.11 Like their fellow researchers in aeronautics, OSRD initially had their hands full with pressing war problems, with little time left for future systems. About 1944, however, an OSRD panel was formed on jet propulsion with Edwin R. Gilliland as its chief. **


Among the studies of the OSRD jet propulsion panel was a very significant one on fuels for jet propulsion reported by Alexis W. Lemmon, Jr., in May 1945.12 The Lemmon report, or "blue book"-from the color of its cover-became a standard reference for researchers in jet propulsion and rocket fuels in the early postwar years. It marked the beginning of such research in the U.S.


For jet engines using the oxygen in air to burn the fuel, as in turbojet and ramjet engines, Lemmon considered eleven hydrocarbons and eleven high-energy fuels in the diborane and borohydride family.*** High-energy fuels yield more heat in burning than conventional fuels, such as gasoline or kerosene, and therefore have the potential for greater performance. Lemmon concluded, however, that little change could be expected in fuels for jet engines using air and that "high density and high heat of combustion fuels will be used for minor applications but no major change from present fuel of gasoline or kerosene is probable."13 In the years to come-extending into the second half of the 1950s-the government spent a quarter of a billion dollars investigating high-energy fuels containing boron and light metals for air breathing engines before abandoning them. Lemmon's early conclusion was right.


On rocket fuels, Lemmon presented the performance of 25 fuel-oxidizer combinations, 14 monopropellants, and 6 solid propellants. **** Separate fuels and oxidizers, when mixed and burned, yield higher energy than either monopropellants or solid propellants. This advantage of higher energy is sometimes offset by the undesirable physical or chemical properties of fuel, oxidizer, or both. Of all the rocket fuel and oxidizer combinations that he considered, Lemmon found that the combination of liquid hydrogen-oxygen gave the highest performance, but he rejected it. "Although the liquid hydrogen-liquid oxygen system has by far the highest specific impulse performance of any system considered in this report, the low average density of the fuel components almost completely eliminates this system from all but very [5] minor applications." 14 Low density meant that large tanks were required, which added mass and drag to the vehicle. Lemmon went on to point out that the development of equipment to produce liquid hydrogen would be difficult, the cost high, and handling hazardous.


On the practical application of liquid hydrogen to flight, Lemmon was proved wrong. In 1958 and 1959, decisions were made to use liquid hydrogen in the upper stage of the Centaur launch vehicle for unmanned space missions and the upper stages of the Saturn launch vehicle for manned voyages to the moon. Both decisions turned out to be sound; both vehicles were remarkably successful. Liquid hydrogen-oxygen emerged as the first high-energy rocket propellant combination to find practical application among many candidates investigated. To explain why and how this happened, and why it took so long, is the purpose of this book.


* A gas turbine engine, the most common form of which is the turbojet, consists of an air inlet, a rotary fan or compressor, one or more combustion chambers, a turbine driven by hot, expanding combustion gases, and a exhaust nozzle. The turbine drives the compressor; the thrust comes from expanding and accelerating the hot air and combustion gases through through the nozzle.
** Other members: Neil P. Bailey, Howard E. Emmons, Ernst H. Krause, Alexis W. Lemmon, Jr., Lloyd W. Morris, John C. Quinn, Edward M. Redding, Theodore H. Troller, Merit P. White, Glenn C. Williams, and Harold A. Wilson.
*** A ramjet engine uses atmospheric air but no mechanical compressor or turbine. Essentially an open duct. the ramjet depends upon high-speed flight and ram air for compression. Fuel is injected and burned and the hot gases expand through a nozzle to provide thrust.
Diborane (B2 H6) and pentaborane (B5 H9) were of great interest in the late 1940s and the 1950s. Lemmon listed as borohydrides compounds containing light metals such as sodium, beryllium, aluminum, and magnesium.
**** A fuel-oxidizer combination, also called bipropellant, is a fuel and an oxidizer which are injected and burned in the rocket combustion Chamber a monopropellant decomposes and gives off heat in the process; a solid propellant contains both fuel and oxidizer elements and burns to yield heat.