Performance Problems in Large Rocket Engines

Extract

In the context of this paper, the term “large rocket engines” refers to those liquid propellant engines at present being built for use with ballistic missiles. The engineers concerned with their development however, are always hoping that the same units may be used for launching satellites and for the early stages of space flight.

Now it is axiomatic that in such vehicles the take-off thrust should exceed the weight. On the other hand, common propellant combinations only give an impulse of about 240 pound seconds per pound of propellants. Thus it follows that the duration of one stage of powered flight at constant thrust could not exceed 240 seconds, even if the net take-off acceleration were zero and the whole missile consisted of propellants. Allowing for sensible take-off accelerations, and for the weight of structure, engines and payload, a more realistic figure would be 150 seconds. As re-use of the engine system is not usually contemplated, the entire operational life of a large rocket engine is probably less than three minutes.