Oxygen-Powered Jet Might Someday Travel The World In 4 Hours If Technology Proves Viable And Meets Actual Market Demand At Acceptable Cost<p>Near as I can tell, the article is mixing up two different things. SABRE is being tested as a rocket engine - it recently got some press on here because they had a successful heat exchanger test which, while pretty cool, does not an engine make. As I understand it since that test the ESA has given the nod to SABRE and believes there isn't any technical reason why the engine won't work.<p>The article mentions that the main advantage will be that "aircrafts can carry less load in terms of on-board liquid oxygen". This is presumably actually referring to rockets, not aircraft, since conventional jet aircraft already use regular old air. "massive throw-away first stages", again, hopefully refers to rockets, otherwise there might be some expensive property damage when your passenger jet drops its first stage on La Guardia.<p>There is an actual passenger jet piece, though. A separate initiative called the A2, a hypersonic passenger jet based on a derivative of SABRE. If built, it could apparently travel at Mach 5 and take you halfway around the world in something like 4.6 hours, which is pretty close to 4 if you squint.<p>All of this stuff is being planned by the same company, and Wikipedia says the plane's coming within 25 years "if there is market demand" - so although this all sounds good, and it's nice they've had a successful test, I think it's safe for now to treat this new oxygen-powered jet as vapourware.<p>(sorry)