Significance

[28] The first experimental investigation of liquid hydrogen as a fuel for aircraft and rockets was started in 1945 by the research arm of the Air Force, as part of a long tradition of searching for new and improved fuels. Hydrogen, the ultimate fuel in energy content, needed to be investigated for its potential application in air-breathing and rocket engines. The availability of hydrogen liquefaction equipment and the experts at Ohio State University provided the catalyst for starting the experimental investigation.

The Ohio State research on hydrogen for air-breathing engines never progressed beyond a few exploratory experiments. These showed that hydrogen burned readily over a wide range of conditions-a result that could have been predicted from earlier work. That more was not done with hydrogen for air-breathing engines could have come from one or more of the following: (1) hydrogen's low density, long its outstanding disadvantage for aircraft applications, as pointed out by Tsiolkovskiy in 1930; (2) rising interest in boron compounds as high-energy fuels for ramjets, as sponsored by the Navy; (3) greater interest in rocket applications by Wright Field; and (4) lack of equipment needed for research on air-breathing engines.

Ohio State University investigators focused their engine research on rocket engines and made many contributions to liquid hydrogen technology. The high performance potential of liquid hydrogen-liquid oxygen was verified, and it was also found that liquid hydrogen was a satisfactory regenerative coolant. Research established that centrifugal pumps were capable of pumping liquid hydrogen to the high pressures needed for rocket engines. It was also found that ball bearings for pumps would operate satisfactorily when immersed in liquid hydrogen without the usual oil lubrication, showing that design of practical pumps was feasible. Pump tests with water produced data that were valid in predicting performance with liquid hydrogen a decided convenience in determining several design parameters. Finally, it was shown that the performance of liquid hydrogen-liquid fluorine was higher than for liquid hydrogen-liquid oxygen, and density was higher also.

With such significant results with liquid hydrogen, then, why did Air Force interest in sponsoring further research begin to wane in the late 1940s? Several possible reasons come to mind, one being the shift in Air Force interest from rockets to air-breathing propulsion in the late 1940s. Another possibility is that the Air Force managers may have felt the exploratory research had fulfilled all of its objectives and without an application, there was no need for further work. There is, also, the ever-present possibility that the sum of all of hydrogen's disadvantages-formidable for military applications-may have overwhelmed Wright Field's attraction to the high energy of hydrogen in the same manner experienced earlier by both Tsiolkovskiy and Goddard.

The scientific and technological progress made at Ohio State with liquid hydrogen served as the foundation for contributions by other groups. Running parallel to Air [29] Force interest in hydrogen as a fuel was Navy interest, which also faded by the end of the 1940s. Unlike the Air Force, however, the Navy had a specific application in mind and its efforts to secure approval to develop a hydrogen-oxygen rocket will be discussed next.