The British government announced on Tuesday that it has authorized an investment of £60 million in Reaction Engine’s Skylon spaceplane. The funding boost comes after a successful feasibility test of a core component of the spacecraft’s revolutionary engine managed by the European Space Agency (ESA) last November and will be used to further develop the revolutionary SABRE engine, which is designed to power the Skylon into orbit and back without the need for outside boosters or tanks.

The Synergistic Air-Breathing Rocket Engine (SABRE) is a scramjet. That is, it reduces the propellant load because it acts as a jet while in the atmosphere and a rocket in space, so it doesn't have to carry as much oxygen to burn the liquid hydrogen fuel. It’s an idea that’s been around since the 1950s, but getting it to work involves overcoming a major technological hurdle.

The problem is that the limit of the engine is how hot it gets. Above a certain point, even the best metal alloys soften and melt. At hypersonic speeds, the air is coming into the engine at 25 times more force than that of a Category 5 hurricane and the heat is like something blasting out of a cutting torch. Paradoxically, before it can be burned, the air needs to be cooled dramatically, so it passes over a series of heat exchangers that use the cryogenic hydrogen fuel to cool it down from 1,000° C (1,832 ° F) to minus 150° C (minus 302 ° F) in 1/100th of a second.

“Ambient air comes in and is cooled down to below freezing in a fraction of a second,” explained Mark Ford, head of ESA’s propulsion section. “These types of heat exchangers exist in the real world but they’re the size of a factory. The key part of this is that Reaction Engines has produced something sufficiently light and compact that it can be flown.”

When the technology passes to the practical phase it will be used to power the 85-meter (278-ft) Skylon, a true spaceplane designed to take off and land from a conventional runway.

Source: ESA