It is now generally recognised that liquid hydrogen offers a considerable increase in vehicle performance over the more conventional fuels, despite its relatively low density.

A design study on an upper stage, which uses a liquid hydrogen/ liquid oxygen chemical propulsion system, revealed a number of problem areas which extend beyond the current levels of experience and knowledge in rocket technology existing in the U.K. This study was made on the third stage of a communication satellite launching vehicle, and a number of the problems high-lighted during the course of the investigation, covering both the propulsion system and the structure, are described and discussed in terms of their importance and their effects on the launcher system. Solutions are suggested where possible—although, lacking practical confirmation, these must be tentative in the circumstances.

While no fundamental difficulties are anticipated in the development of a rocket engine using hydrogen, it is essential to accumulate some background of data and experience to ensure that early policy and designs are sound; the importance of beginning practical work as soon as possible is emphasised.