28 Mar 04. The FT reported that space scientists from Nasa on Sunday claimed a breakthrough after an aircraft with a revolutionary jet engine flew at seven times the speed of sound.
The successful flight of the X-43A – an unpiloted, 12-feet-long cross between a spaceship and an aeroplane that looks like a winged surfboard – was hailed as a significant advance for space travel and long-haul civil aviation.Nasa, the US space agency, said it could eventually lead to more frequent and lower-cost space travel and shorter travel times for inter-continental flights.
In Saturday’s flight off the California coast, the X-43A was carried to a height of 40,000 feet under the wing of a B-52 bomber. Rocket boosters then propelled it up to 95,000 feet before it flew under its own power. The craft then exceeded Mach 7, about 8,000 km/hr, for some 11 seconds before plunging into the Pacific Ocean.
“A little over 100 years ago, a couple of guys from Ohio flew for 40 metres in the first controlled power flight,” said Lawrence Huebner, lead propulsion engineer, referring to the Wright brothers. “We did something very similar in the same amount of time, but our vehicle under air-breathing power went over 20km”. The X-43A project centres on the craft’s “scramjet” – or supersonic combustion – engine, which straddles the gap between conventional jet and rocket propulsion. Previously, speeds of Mach 5 – five times the speed of sound – were only possible using rocket technology, where both hydrogen fuel and the oxygen it burns are carried on board.
The X-43A is “air-breathing” like a conventional jet engine. Its fuel tanks carry only hydrogen and the oxygen it needs for combustion is pulled from the atmosphere. Although there are few or no moving parts involved, the supersonic air-flow through the engine means achieving proper ignition and combustion is a considerable engineering challenge. Nasa said the value of the $250m project lay in the weight savings to be made from not carrying heavy tanks filled with oxygen. This could make space travel more efficient by increasing the payload capacity of reusable space launch vehicles, increasing their range or reducing their size for the same payload. Scramjet engines could also be more flexible since they have much better throttle response than normal rockets. Later this year, Nasa hopes to test the X-43A at Mach 10, or about 11,000 km/hr.
The flight of NASA’s X-43A at seven times the speed of sound got a lift from Boeing research expertise with hypersonic vehicles and spacecraft.
Boeing Phantom Works is teamed with prime contractor ATK GASL to develop and build the X-43A or Hyper-X for NASA. Boeing designed the vehicle, the airframe thermal protection systems and flight control and navigation systems. ATK GASL was responsible for vehicle fabrication, assembly, systems integration and testing in addition to providing the scramjet engine. The booster is a modified Pegasus rocket built by Orbital Sciences Corp.
Hypersonic flight, defined as flying at least five times the speed of sound, remains a mostly unexplored region. At those speeds, metals can melt or vaporize almost instantly, and aerodynamic control must be extremely precise. Additionally, strong shockwaves are created that can cause exceptionally high temperatures and forces on various parts of the airframe.
To meet these challenges, the X-43A employs a tile-based thermal protection system, carbon-carbon composites, and high temperature-resistant metals; a control system designed to deal with the rapid changes in forces and motions expected at Mach 7; and a special control technique to sense and prevent disruption of the supersonic airflow through the inlet, which would dramatically reduce engine thrust. Boeing has explored the challenges of hypersonic flight since the 1950s, beginning with the X-15 to the space shuttle to the X-43A. Phantom Works is currently teamed with P