FLUG REVUE June 2004: X-43A fies Mach 7 record mission

WORLD RECORD FOR HYPER-X

By Matthias Gründer

After the first hypersonic X-43 research vehicle had had to be destroyed due to technical problems shortly after separation of the booster rocket from the launch vehicle, the second attempt by NASA engineers was finally crowned with success.

X-43A launch from B-52

The second of the three X-43A research vehicles which have been built was supposed to prove that such a scramjet (supersonic combustion ramjet) can achieve speeds of this order of magnitude. A ramjet operates by subsonic combustion of fuel in a stream of air compressed by the forward speed of the aircraft itself. A scramjet is a ramjet engine in which the airflow through the engine is supersonic.

After the botched premier, the second attempt was actually originally scheduled for the middle of last year, but the accident investigation delayed matters. It was not until the autumn of 2003 that the causes of the crash were clarified – a defective flight profile, in which for cost reasons the Pegasus booster rocket had been released at too low an altitude. As a result it had been exposed to twice the dynamic pressure during the transonic flight phase, leading to excessive vibration and destabilisation of the control system.

Preparations for the critical test were now extremely thorough, and although the X-43 team gave the go-ahead for the test in February 2004, there was a further delay due to a rudder actuator problem on the Pegasus booster. Despite this, on 27 March at 12.40am local time the B-52B launcher took off from the runway of Edwards Air Force Base in the Mojave desert, California, bound for the Western Test Range, a military testing area some 650km to the west of the Dryden Flight Research Center, above the Pacific.

It took 20 minutes to get to the launch zone, where the booster was released at an altitude of about 12km. This altitude was necessary in order to ensure that the X-43's initial velocity would be sufficiently high, about Mach 5, for its engine to function properly. The Pegasus carried its uncovered payload, mounted at the vertex, to an altitude of about 31km, at which point it then released it with ultra-precision for its mission.

Built by ATK GASL, formerly known as MicroCraft Inc. in Tullahoma, Tennessee, the X-43A had already achieved an initial velocity of around 5,600km/h, enough to sufficiently compress the air flowing through the engine. All that now remained to accelerate the 3.75m long, 1.3t air vehicle on a 22km trajectory at a peak speed of Mach 7.7 was for the fuel carried to be injected and combusted in a burning time of about 10 seconds. Up to now the world record for a jet-propelled aircraft had been held by an SR-71, which in 1976 had attained the then incredible speed of 3,529km/h.

Already the engineers from the Langley Research Center and the Dryden Flight Research Center of NASA, the manufacturer and the Boeing Phantom Works, which had been responsible for the design, thermal protection and onboard systems, had every reason to celebrate. But the mission was not over yet. On the subsequent, approx. six minute long unpowered descent, the X-43A transmitted additional measurement data gathered from over 500 installed sensors before sinking irretrievably into the depths of the Pacific after a total flight of 650km. Due to financial constraints, there have never been any plans to salvage the wreckage.

TESTS BENEFIT THE MILITARY

Chief engineer Griffin Corpening was extremely satisfied with the test results and pointed out that these would shortly be made available in their entirety to industry and the military. That is still not the end of the programme, as the third X-43A remains to be launched later this year and should reach Mach 10.

However, that will probably bring research under the Hyper-X programme to an end for the time being, whereas NASA had once had hopes of making discoveries through this programme that would pave the way for novel forms of spacecraft propulsion. Plans to develop a further variant, which would be known as the X-43C, have been put on the back burner, given that President Bush's spaceflight plans are geared towards the development of new, manned spacecraft. NASA managers are doubtful that funding for such tests will be available in the future. To date the trials have cost $250 million.

Whereas previous NASA plans included not just fast space shuttles on low earth orbit but also revolutionary passenger aircraft for the installation of scramjets, which from 2050 or so would be capable of reaching any point in the earth in a mere two hours' flying time, civilians will no doubt have to continue to make do with conventional propulsion systems for the time being.

Meanwhile the military are already very interested in the lightning-quick flying vehicles, but President Bush is calling for the development of unmanned combat air vehicles to assist with the “global war on terror”. By a strange coincidence, these are required to be capable of effectively attacking targets anywhere in the world within two hours. So it is virtually certain that sufficient funds will be found in the Air Force budget for further leading research work.

From page 84 of FLUG REVUE 6/2004

Last updated 7 May 2004

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