Reaction Engines’ precooler has successfully run at Mach 5 temperatures, validating for the first time the capability of the novel heat exchanger design to operate at hypersonic flight conditions for atmospheric and space access applications.

The breakthrough test is pivotal to Reaction’s goal of using the lightweight heat exchanger (HTX) to boost high-speed turbojets for supersonic and hypersonic vehicles as well as for developing the company’s Synergistic Air-Breathing Rocket Engine (Sabre), which is targeted at low-cost, repeatable access to space.

Forming the culmination of a DARPA contract awarded in 2017, the Mach 5 run took place in the second week of October at the company’s TF2 test facility at the Colorado Air and Space Port near Watkins. Established on an all-new site just 22 months ago, the high-speed test comes seven months after the heat exchanger demonstrated operation at supersonic conditions equal to Mach 3.3. Heated air for the tests is generated by a General Electric J79, which operated at military power for the supersonic runs and in maximum afterburner for the tests up to Mach 5.

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The precooler is made up of 16,800 thin-walled tubes (equal to more than 27 mi. of tubing) through which helium is pumped to remove heat. In the Colorado tests, the heat is rejected into water that boils off to the atmosphere, but in a Sabre it would be cooled by a hydrogen heat exchanger. “In the Mach 5 test, the temperature was reduced from around 1,000C to roughly 100C in less than 1/20th of a second,” says Dissel.

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For high-speed turbojet applications in the nearer term, the HTX significantly reduces compressor delivery temperature (T3). This maintains sea-level conditions in front of the compressor over a wider range of speeds, thus maximizing net thrust. For space access applications, the HTX will pass chilled air to a turbo-compressor and into a rocket thrust chamber, where it will be burned with subcooled liquid hydrogen fuel.

I find this technology really cool.

While right now, they are testing with liquid hydrogen fuel for launches to orbit, I’m think that liquid methane would likely be used for any potential hypersonic transport or air breathing weapon.