For a spaceflight revolution? 'The design comprises a single combined cycle rocket engine with two modes of operation.[4] The air breathing mode combines a tur

For a spaceflight revolution? 'The design comprises a single combined cycle rocket engine with two modes of operation.[4] The air breathing mode combines a turbo-compressor with a lightweight air precooler positioned just behind the inlet cone. At high speeds this precooler cools the hot, ram-compressed air leading to an unusually high pressure ratio within the engine. The compressed air is subsequently fed into the rocket combustion chamber where it is ignited with stored liquid hydrogen. The high pressure ratio allows the engine to continue to provide high thrust at very high speeds and altitudes. The low temperature of the air permits light alloy construction to be employed which gives a very lightweight engine—essential for reaching orbit. In addition, unlike the LACE concept, SABRE’s precooler does not liquefy the air letting it run more efficiently. ... The combination of high fuel efficiency and low mass engines permits a single-stage-to-orbit approach, with air breathing to mach 5.14+ at 28.5 km altitude, and with the vehicle reaching orbit with more payload mass per take-off mass than just about any non-nuclear launch vehicle ever proposed' https://en.wikipedia.org/wiki/SABRE_(rocket_engine) https://en.wikipedia.org/wiki/SABRE_(rocket_engine)