Reaction Engines' hypersonic SABRE air-breathing rocket engine has taken a major step towards flight after a key component passed the first phase of high-temperature testing. Under conditions simulating supersonic flight, the engine's precooler unit quenched a 420° C (788° F) intake airflow in less than 1/20th of a second.

The Synergetic Air-Breathing Rocket Engine (SABRE) engine is a hypersonic hybrid design that draws in air like a conventional jet while accelerating to speeds of up to Mach 5 (3,704 mph, 5,961 km/h), then converts to a pure rocket engine burning hydrogen and liquid oxygen, making speeds of up to Mach 25 (17,521 mph, 29,808 km/h) possible.

The idea is that by breathing air during low-speed acceleration, SABRE can drastically reduce the amount of oxidizer needed to feed the engine, reserving liquid oxygen for only the hypersonic, high-altitude phase when it acts like a pure rocket. In this way, SABRE can power hypersonic aircraft or even orbiters like the Skylon spaceplane.

The problem is that when the air is coming in at supersonic speeds, it has a force 25 times that of a category 5 hurricane, generating temperatures that would melt any material that the engine might be made of. It's for this reason that the precooler unit is so vital to the SABRE engine's operation as it will one day use recirculated cryogenic hydrogen fuel to cool incoming air down from 1,000° C (1,832° F) to -150° C (-302° F) in 1/100th of a second.

The current tests that began in early March were nowhere near that range. According to Reaction Engines, the test at the company's TF2 test facility at the Colorado Air and Space Port in Aurora, Colorado used a General Electric J79 turbojet engine originally built to power the McDonnell Douglas F-4 Phantom to feed air into the precooler at the equivalent to Mach 3.3 (2,127 knots, 2,448 mph, 3,939 km/h) or the speed of the SR-71 Blackbird aircraft.

Reaction Engines says the compact precooler worked as expected and managed a heat transfer of 1.5 MW, or equivalent to the energy demands of 1,000 homes. Later tests will simulate Mach 5 flight. It has also been extensively tested at the TF1 test facility at Westcott, Buckinghamshire, UK, where it operated under ambient air temperatures. It's at TF1 that the engine core is being tested.

"This is a hugely significant milestone which has seen Reaction Engines' proprietary precooler technology achieve unparalleled heat transfer performance," says Mark Thomas, Chief Executive, Reaction Engines. "The HTX test article met all test objectives and the successful initial tests highlight how our precooler delivers world-leading heat transfer capabilities at low weight and compact size. This provides an important validation of our heat exchanger and thermal management technology portfolio which has application across emerging areas such as very high-speed flight, hybrid electric aviation and integrated vehicle thermal management."

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