EADS revealed the proposal at the Le Bourget air show (June 18, 2011). It is expected to fly at mach 4, 32km above the ground, and it will carry 50 to 100 people. It will combine three propulsion systems: two turbofans for take-off and up to Mach 0.8, then rocket boosters up to Mach 2.5, then two underwing ramjets would accelerate it to Mach 4.
The so called Zero Emission Hypersonic Transportation (Zehst) system notionally should fill the high-end market niche left unmet since the retirement of Concorde, says Jean Botti, chief technical officer at EADS.
Technology underpinning Zehst still would require some time to mature, with a commercial offering not expected to emerge until around 2040, but Botti says an unmanned technology demonstrator could already be flying in about ten years to help validate the concept. EADS officials are not pushing a military application, but acknowledge that may be possible.
Despite the use of three propulsion systems, Botti argues the system will not be cost prohibitive. “I am not sure that this equation will be that expensive,” he says, noting that does not mean it would be cheap either. One reason is that the rocket motors are relatively small, merely aimed at giving the aircraft a boost, rather than lifting the entire vehicle from a standing start. “I don’t think it is that complex,” Botti says of the system.
The maximum acceleration the passengers would be exposed to is around 1.2g.
Botti says one of the program goals is to minimize emissions and also limit the impact of the sonic boom by trying to direct it to have a small footprint on the ground.