Reaction Engines is presently engaged on an EU 50% funded project as part of Framework 6. This study is to examine the propulsion concepts and technologies required
"...to reduce long-distance flights, e.g. From Brussels to Sydney, to less than 2 to 4 hours. Achieving this goal intrinsically requires a new flight regime for commercial transport with Mach numbers ranging from 4 to 8."
To fulfill this mission, a hypersonic aircraft with near antipodal range (20,000 km) is required. To achieve the range requirement liquid hydrogen fuel is mandatory since the specific calorific energy of hydrocarbon fuels is too low. Reaction Engines have conceived the Scimitar pre-cooled engine concept which exploits the unique thermodynamic properties of liquid hydrogen.
This engine is capable of sustained Mach 5 flight whilst achieving an effective exhaust velocity of order 40,900 m/s. In addition the engine has a second operating mode that features a high bypass airflow permitting efficient subsonic flight and moderate take-off noise.
For more on this aircraft, visit Reaction Engines - LAPCAT A2