Reaction Engines in the UK have been developing a space plane for two decades and they made progress on the core technology.

The Foreign Comparative Testing campaign was a success. Reaction Engine's joint U.S. and UK team achieved over 10 megawatts of transferred thermal energy using the same style of precooler tested under the HTX campaign. This result was more than three times the energy transfer achieved in our previous test program. The results from this test further expand the operational envelope of our heat exchanger technology and prove its rightful place in the high-Mach regime.

They will develop an air breathing engine. This will mean they will not need to carry the liquid oxygen. Liquid oxygen is most of the mass for rocket fuel.

Traveling at high speeds heats up the air. They need to cool the air very rapidly to make an efficient hypersonic engine.