today

The European Union (EU) has agreed further funding for a European civil hypersonics project whose goal is to achieve passenger flights from Brussels to Sydney in "two to four hours", at speeds of Mach 4 to 8. A proposed hydrogen-fuelled hypersonic airliner catchily dubbed "Configuration A2". The A2 would be powered by Scimitar engines, a modified version of previous plans for a Single-Stage-to-Orbit reuseable spaceplane drive called Sabre. "essentially a... rocket engine with an additional precooled turbo-compressor". The use of almost-liquefied air from the turbo will allow Scimitar/Sabre propulsion to operate without onboard liquid oxygen up to Mach 5.5. Unlike a ramjet or scramjet, this kind of engine can fire up happily while stationary on the runway, too, removing the need for a separate booster to get up to ignition speed. It would also feature a special high-bypass mode, allowing it to operate fuel-efficiently at subsonic speeds. This would permit the economic use of longer overland routes, something which Concorde couldn't really do.

IMO: It may operate from hydrogen but surely it can hardly be considered "green" if used for routine business flights as envisaged. It looks like turning back the clock, how about really adequate teleconferencing at a lot less cost, or isn't that amusing enough for the faceless Brussels bureaucrats.