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The Zero Emission Hyper Sonic Transport[1] or ZEHST[2] is a planned hypersonic passengerjet airliner project by the multinational aerospace conglomerate EADS and the Japanese national space agency JAXA.[3]
On 18 June 2011, the ZEHST concept was unveiled by EADS at the Le Bourget Air Show. The envisioned vehicle uses a combination of three different types of engines, including relatively conventional turbofans, rocket motors, and scramjets to attain a maximum speed of Mach4.5 (four and a half times the speed of sound).[4][5] The ZEHST has been projected to carry between 50 and 100 passengers while flying at very high altitudes for greater efficiency.[4]
Conceptually, the ZEHST has been promoted as a descendant of, or a successor to, Concorde, a supersonic airliner that was withdrawn from passenger routes in 2003.[5] According to projections released, the ZEHST would be capable of flying between Paris and Tokyo in 2.5 hours, or between New York and London in one hour.[6][7] In 2011 EADS predicted that the ZEHST could be flying by 2050,[4] according to an article in SuperBlondie revising the prediction in 2024 to 40 years from then.[7]
Development
Even before the introduction of the Concordesupersonic airliner during the 1970s, the aviation industry has wanted to produce high-speed transport aircraft. Since the 1990s, several collaborative research efforts in the field have been financed in Europe.[8] By the 2010s, both the American aerospace company Boeing and the multinational aerospace conglomerate EADS were reportedly working on separate plans to develop hypersonic aircraft.[4][5] Such efforts have largely been constrained to theoretical work, but some progress has been observed over the decades, and innovations have continued to be patented in the field, such as a patent for a mixed-propulsion arrangement awarded to EADS in 2010.[9] Amongst other aspects, efforts have been made to reduce noise generated by the sonic booms commonly produced by aircraft flying at supersonic speeds.[5][10]
On 18 June 2011, EADS revealed the Zero Emission Hyper Sonic Transport (ZEHST) concept at the Le Bourget Air Show.[11][12] As originally announced, the aircraft would combine three distinct propulsion systems: two turbofan engines for taxiing, take-off, and up to Mach0.8; then rocket boosters up to Mach2.5, afterwards switching to a pair of underwing scramjets to accelerate up to its maximum speed of Mach4.5 (four and a half times the speed of sound).[5][13] The fuel of these engines is envisaged to be a biofuel primarily made out of seaweed,[1] along with a combination of oxygen and hydrogen.[4] Largely due to this fuel composition, the aircraft has been referred to as a "green" aircraft that generates "almost zero emissions".[14][15]
The ZEHST has an unusually high cruising altitude of 32km, flying within the outer atmosphere, compared to the 11km of conventional airliners; this altitude was chosen because the air is thinner and causes less drag.[4] The use of conventional turbofan engines during takeoff would make the ZEHST quieter than conventional airliners. The ZEHST's configuration has not been finalised[when?].[4] In addition to EADS itself, much of the propulsion-based development work on the ZEHST project had been made in cooperation with the European missile specialist MBDA and the French national aerospace research centre ONERA.[8] International engagement also secured partners; the cooperative HIKARI R&D project is underway between Japanese and European agencies.[8] The ZEHST is not the only such effort that the company has engaged in; by 2015, Airbus Group (EADS's new name) was reportedly working on two hypersonic projects, one in conjunction with Japanese partners and the other with Russian and Australian involvement.[5] That same year, Airbus chief executive Tom Enders stated his support for development of a hypersonic long range passenger transport.[16]
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