History
The precooler concept is due to an idea originated by Robert P. Carmichael in 1955. This was followed by the liquid air cycle engine (LACE) idea which was originally explored by Marquardt and General Dynamics in the 1960s as part of the US Air Force's aerospaceplane efforts.
In an operational setting with LACE, the system was to be placed behind a supersonic air intake which would compress the air through ram compression, then a heat exchanger would rapidly cool it using some of the liquid hydrogen fuel stored on board. The resulting liquid air was then processed to separate out the liquid oxygen for burning in the engine. The amount of warmed hydrogen was too great to burn with the oxygen, so most was to be simply dumped overboard (nevertheless giving useful thrust.)
In 1989, after funding for HOTOL ceased, Bond and several others formed Reaction Engines Limited to continue research. The RB545's precooler had issues with embrittlement, relatively high liquid hydrogen consumption, patents and Official Secrets Act, so Bond went on to develop SABRE in its place.
As of November 2012, hardware testing of the "heat exchanger technology crucial to hybrid air- and liquid oxygen-breathing rocket motor" has been completed. This was an important step in the Sabre development process, as it demonstrates to investors that the technology is viable. The Sabre engine "relies on a heat exchanger capable of cooling incoming air to −150 °C (−238 °F), to provide liquid oxygen (LOX) for mixing with hydrogen to provide jet thrust during atmospheric flight before switching to tanked LOX when in space." The successful tests validate that the critical heat exchanger technology can perform as needed for the engine to obtain adequate oxygen from the atmosphere to support the low-altitude, high-performance operation.
The next stage of the SABRE engine programme includes ground testing a sub-scale engine able to demonstrate the entire cycle; ESA has expressed it's confidence that the demonstrator can be successfully built, and has declared that it would represent "a critical milestone in the development of this program and a major breakthrough in propulsion worldwide."
Read more about this topic: SABRE (rocket Engine)
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