Hypersonic travel, and maybe even a new type of orbital launcher, has come closer to reality after Boeing and Rolls-Royce today announced substantial investments in the British advanced propulsion systems company Reaction Engines Limited (REL). Part of a US$37.3 million Series B funding round that also included BAE Systems, it follows a £60 million (US$85.6 million) investment in the company by the British government in 2013.
Reaction Engines has been working on its plans for a hypersonic spaceplane long before the company was founded in 1989. Based on the work of engineer Alan Bond, it began life as the HOTOL project, which was a joint project by Rolls-Royce and British Aerospace. When that fell through due to technical problems, Bond, along with engineers John Scott-Scott and Richard Varvill, formed REL, which has concentrated for the past 29 years on developing variants of the Synergetic Air-Breathing Rocket Engine (SABRE) engine.
The main component of REL’s Skylon spaceplane, SABRE is a hypersonic hybrid engine that acts like a conventional jet at speeds below Mach 5 (3,704 mph, 5,961 km/h), but at hypersonic speeds it converts into a pure rocket engine burning hydrogen and liquid oxygen to achieve speeds of up to Mach 25 (17,521 mph, 29,808 km/h). Key to this is a revolutionary heat exchanger that protects the engine against melting as it approaches hypersonic velocity.
At speeds approaching Mach 5, even the best metal alloys soften and melt, and at hypersonic speeds, the air coming into the SABRE engine has 25 times the force of a Category 5 hurricane and heat like something blasting out of a cutting torch. This means that the incoming air needs to be cooled dramatically, so it passes over a series of ultralight heat exchangers that use the cryogenic hydrogen fuel to cool it down from 1,000° C (1,832° F) to -150° C (-302° F) in 1/100th of a second.
Such an engine could be used to launch payloads into orbit using the reusable Skylon spaceplane, but what is probably most attractive to Boeing through its HorizonX ventures initiative is its potential application for hypersonic point-to-point commercial travel.
“As Reaction Engines unlocks advanced propulsion that could change the future of air and space travel, we expect to leverage their revolutionary technology to support Boeing’s pursuit of hypersonic flight,” says Steve Nordlund, vice president of Boeing HorizonX.