¶SABRE engine gets the green light. UK-based Reaction Engines’ air-breathing hybrid ramjet/rocket engine received investment from the ESA (€10m) and UKSA (£50m). The air-breathing phase of launch can take the proposed autonomous Skylon SSTO vehicle 22% of the way to orbital velocity, allowing the vehicle to carry 40% less oxidizer mass, thus increasing its relative payload capacity and making SSTO plausible. SABRE’s core technology is its insane pre-cooler which is rated at over 1 GW/m3 of heat transfer. It can cool super hot compressed intake air that is moving at up to Mach 5.4 by ~1000° K in a twentieth of a second, allowing the engine to be built out of the lighter weight alloys critical to attaining orbit. By using helium in the pre-cooler, and then running it through a heat exchanger with incoming cryogenic hydrogen propellant, the engine avoids challenges with hydrogen embrittlement that would compromise its 50 km (!!) of 30 micron-walled tubing. While recent coverage touts SABRE as ‘new’, Reaction Engines was established in 1989 to continue work on a canceled British Aerospace Horizontal Take-Off and Landing vehicle that was conceived of in 1982 as a cheaper alternative to the Space Shuttle. Testing SABRE’s pre-cooler was funded by DARPA in 2017. They’ll be conducting high-temperature airflow tests by shooting exhaust from an F-4’s turbojet engine into the pre-cooler at 1000° C. Look for this testing to begin in the next month or so.