The US air force and NASA have launched a joint research push to advance hypersonic flight technology. The air force research lab and space agency are seeking university and industry partners, and are offering $30m in funding.
Hypersonic for this purpose is defined as five times the speed of sound or faster. Thus far, very few vehicles have operated in such flight regimes. In general, when seeking to move extremely fast around the world, it is more normal to lift a craft out of the atmosphere on a rocket - as in the case of intercontinental missiles. A few jet aircraft can briefly exceed Mach 3 (the MiG-25 Foxbat interceptor could do so just once if required, knackering its engines in the process), and the famous turbo-ramjet SR-71 "Blackbird" Cold War spyplane could reach such speeds repeatedly. But so far no known runway-landing, air-breathing plane has beaten Mach 4.
"We have identified three critical research areas: Air-breathing propulsion, materials and structures, and boundary layer control," said James Pittman, top NASA hypersonics boffin, in a statement released yesterday.
"These three areas are the biggest hurdles to successful hypersonic flight and low-cost space access using an air-breathing engine."
NASA has longed hoped to develop reliable aircraft which could take off and land on runways, and fly many times faster than sound while still inside the atmosphere using air-breathing engines. Such planes would avoid one of the big problems of today's orbital-launch rockets - the need to carry oxidiser as well as fuel. An airbreather engine could instead use oxygen from the atmosphere, saving large amounts of weight.
The hope is that re-usable hypersonic space planes of tomorrow might accelerate almost to orbital speed needing very little oxidiser, perhaps mainly using relatively ordinary jet fuel rather than exotic rocket juice. All this could cut down the present enormous costs of access to space - or alternatively allow the military's missiles, planes etc. to go a lot faster.
But the problems of getting fuel to burn in a hypersonic airstream are huge, and so is the matter of preventing an airframe from simply melting when shoved through relatively dense air at terrific speed. Then, as Pittman says, there's the matter of boundary layer control - preventing dangerous turbulence developing close to the speeding aircraft, which could easily wreck it or send it out of control.
The Pentagon's famous bad-boy scientists, DARPA* - who slap the pendulous jowls of established wisdom with the gauntlet of disregard - had previously suggested that all these issues could be sorted out on the fly. DARPA's wingnut-boffins reckoned they should be given $750m from 2009 to get on with building a runway hyperjet which would be able to barrel-roll at Mach 6. However, sceptical politicos on Capitol Hill have given the so-called "Blackswift" project a severe trimming, making near-future success even more doubtful than it would be ordinarily.
It now appears that NASA and the USAF reckon to commit relatively minor funds to basic research before starting work on any actual aircraft. There's more on becoming a National Hypersonic Science Center and getting hold of the grant money here. ®
* The Defence Advanced Research Projects Agency.