Propulsion technology mostly unchanged after 50 years

Although it's been a half century since America entered the space age, the basic propulsion concepts used to push Explorer I into space will be the same type of propulsion that the nation will use to begin the next half century of space exploration.

It was 31 January 1958 when a Redstone-Jupiter C rocket developed in Huntsville, Ala., lifted the 30-pound artificial satellite into space.

Clark Hawk, director of the Propulsion Research Centre at The University of Alabama in Huntsville (UAHuntsville) has seen most of the advances that have taken place in rocket propulsion. He has spent 50 years conducting research in the field.

'Chemical propulsion will be with us for the foreseeable future as the means to escape the Earth's gravity,' said Dr Hawk, who worked with the Air Force Propulsion Laboratory at Edwards Air Force base, before joining UAHuntsville nearly 20 years ago.

'Large forces are required for periods of several minutes to accomplish this and chemical systems do this well and relatively cheaply,' he said.

Hawk, however, concedes there have been technological strides that make current propulsion systems superior to those early engines.

NASA is making plans to return to the moon in the next decade. The nation's space agency is using rocket motors similar in design to the Saturn launch vehicles but will incorporate newer features. These new engines, called J-2 during the 1960s development of Saturn vehicles, will be called J-2X.

'There have been advances in materials and hardware design that one might wish to incorporate into the J-2X,' Hawk said. 'For example, the coolant of the J-2 thrust chamber passed through a number of tubes arranged in parallel. The new design would use the milled channel fabrication method used on the space shuttle main engine.

'It features improved heat transfer through the use of copper alloy materials and the 'fin effect' attendant to that design concept. The injector, which is the heart of the engine, would benefit from advancements in understanding of the effects of various design features upon performance and combustion stability since the initial development of the J-2.'

Hawk's research centre at UAHuntsville has unique research capabilities that will provide NASA and contractors a greater measure of safety and performance. 'We have the ability to run rockets on campus with both liquid oxygen and liquid methane. Also, we have a unique combustion stability research tool of which there are only three in the world and ours is the only one in the U.S.A.

'This gives us a research tool for evaluating the combustion stability of a single, full scale, injector element,' Hawk said. 'We could, conceivably, test a variety of injector designs of interest to NASA in order to evaluate their combustion stability characteristics.

'The bench scale hardware is a low-cost approach to obtaining data applicable to full scale injector elements and would facilitate through evaluation of a number of concepts to help identify the most promising designs. Having better knowledge of an injector's susceptibility to combustion instability is an essential ingredient to arriving at a design that will enhance mission safety.'

Meanwhile, as UAHuntsville continues to look at ways to make improvements in chemical propulsion technologies, the university's researchers continue to investigate future propulsion concepts.

'The application of advanced propulsion concepts such as plasma propulsion devices or others that rely upon energy sources other than chemical is for in-space use,' Hawk said. However, he explained that while NASA is not actively pursuing these devices currently, the university continues that research.

'We continue to work such advanced devices to continue to provide better understanding of the associated physics so that when NASA is able to bring its attention to the next level of propulsion needs, we will have provided a foundation from which to build.'