Part II : 1950 -1957

5. NACA Research on High-Energy Propellants



Conference on Propellant Selection


[76] Apparently as a direct result of the visit by Wright Field officials, the NACA called a meeting of rocket experts at the Lewis laboratory on 19 May 1950 to discuss the selection of rocket propellants for long-range missiles.12 A secondary purpose was to use the meeting as a "test run" to determine if a NACA subcommittee on rockets was desirable and feasible.


Propellant selection for any mission is always a compromise between performance and other desired characteristics such as density, cooling capacity, storability, handling, and availability (appendix A-4). The selection process had advanced through several levels of sophistication. The simplest method used exhaust velocity as the criterion, since range varies approximately with the square of exhaust velocity. This ignores the effect of propellant density, which affects tank and vehicle size and mass. In 1947, Richard Canright of the Jet Propulsion Laboratory developed a method of relating exhaust velocity and propellant density for large rockets and found that exhaust velocity was the more important of the two. Combinations using liquid hydrogen ranked the highest, although Canright favored hydrazine for its overall characteristics (p. 47-48). Later studies involved more complex considerations of missile design and flight than Canright's, but all suffered from lack of data that could be obtained only when rockets were designed, built, and flown.


In addition to the major flight parameters, the military was very interested in the logistics problems of propellants-such characteristics as vapor pressure, freezing point, stability during storage, corrosiveness, toxicity, availability, and cost.


At the Lewis meeting, the military representatives and their contractors presented their views and research results. The NACA-Lewis recommendation for propellants, presented by the author, consisted of a primary selection and alternatives. The primary fuel was liquid hydrogen and the primary oxidizer was liquid fluorine. If propellant density proved too great an obstacle for liquid hydrogen in a practical application, the alternate fuels selected were hydrazine, ammonia, or a mixture of the two. The Lewis choice of alternative oxidizer was oxygen.


The NACA recommendation, its first firm choice of liquid hydrogen as a rocket fuel, was not opposed by anyone at the meeting. After all, the selection was for research [77] purposes, not for a development. The selection of alternatives reflected the uncertainty over the effect of fuel density on long-range missile design and performance. The NACA position satisfied both those who believed in the potential of liquid hydrogen and those who did not.


Views about using liquid fluorine, however, varied considerably. During the morning session, William Doyle, of Ohio State University, listened with growing impatience to presentations by Rocketdyne and Aerojet on their fluorine experiments. As a strong advocate of both liquid hydrogen and liquid fluorine, he felt that the presentations were too pessimistic. He could hardly wait to rebut them, but lunch intervened. After lunch, the meeting chairman, Abe Silverstein, noted the meeting was behind schedule and cancelled discussion of the morning papers. This was too much for the peppery Doyle who jumped to his feet, announced that he knew more about fluorine than anyone else present, and proceeded "to lambast the hell out of the two fluorine papers" for their pessimism. Silverstein allowed Doyle to make his point before clamping down.13


Following the May propellant selection meeting, the NACA rocket group planned experiments with liquid hydrogen but faced the familiar problem: how to get a supply of it. Obtaining dewars of liquid hydrogen from Herrick Johnston at Ohio State University and transporting them to Cleveland was rejected as impractical. Since it was not available commercially, the only course open was to build a liquefier at the laboratory. Since the money needed was too much to come from operating funds, the NACA, for the first time, went to Congress in 1951 with a request specifically for rocket research. The fiscal year 1952 budget for construction of facilities contained an item of $150 000 to buy a hydrogen liquefier and a building to house it. The justification stated in part:


Of the chemical combinations that are available as propellants for rocket engines for maximum range, liquid hydrogen offers great potentialities. With certain oxidizers liquid hydrogen has the greatest thrust-per-pound propellant flow [exhaust velocity] of any of the chemical combinations, an important factor for long flight. Insufficient experimental research has been done in this Nation on the use of liquid hydrogen with suitable oxides [sic].... Although there are no commercial cuppliers of liquid hydrogen, simple liquefaction equipment developed during the war, is available commercially.14


Congress approved the request and NACA contracted with the Arthur D. Little Company of Cambridge, Massachusetts, for a hydrogen liquefier scaled up from a Collins cryostat. The company ran into some difficulties which delayed delivery, and the NACA spent the interim period investigating other high-energy rocket propellants.