The engine functions as both an air breathing jet, and then switches to use stored liquid oxygen, as does a rocket engine. Their studies show that single stage to orbit rocketry is possible with that engine. Also, an aircraft with such rockets can reach Mach 5, so that a journey halfway around the world would only require 4 or 5 hours.
The SABRE engine incorporated in a new aircraft, known as Skylon, could potentially be used to deliver satellites to orbit, and would then return to earth. The engines are designed to operate much like a conventional jet engine at up to around Mach†5.5 at 26 km altitude. Then, air inlet closes and the engine operates as a highly efficient rocket to orbital speed. The proposed SABRE engine is not a scramjet, but a jet engine running combined cycles of a precooled jet engine, rocket engine and ramjet. The key technology for this type of precooled jet engine is a light weight heat exchanger.
In a Nov. 28 press release, Reaction Engines announced successful tests of such a heat exchanger. More than 100 test runs have been completed. The tests were funded and overseen by the European Space Agency. The heat exchanger uses liquid helium to cool air from 1,000 degrees Celsius to about minus 150 degrees Celsius. And there is no frost problem with the exchanger.