Failures of trim controls for pitch, yaw and roll set back Scaled Composites' bid for to take $10 million X-Prize
Scaled Composites' drive to claim the $10 million Ansari X-Prize is on hold while the company scrutinises a series of critical malfunctions tarnishing SpaceShipOne's breakthrough suborbital flight on 21 June.
Pilot Mike Melvill credits back-up flight controls for stabilising his craft after trim controls for pitch, yaw and roll failed as he neared the ascent's apogee of 328,491ft, slightly above the 100km threshold for space. Melvill says he noticed the problem while trying to trim the nose to gain even more altitude as he approached the top of his climb.
In 5s of uncontrolled flight, says Melvill, SpaceShipOne slanted about 22 miles off-course as it began a Mach 2.9, 5g re-entry into the atmosphere. The vehicle's north-east trajectory over the isolated Mojave Desert swerved to the south, closer to more urban areas. Scaled Composites founder Burt Rutan acknowledged the deviation violated a 5 mile "airspace box" imposed by the US Federal Aviation Administration.
Melvill's successful recovery allowed Scaled Composites and financier Paul Allen, co-founder of Microsoft, to break the space barrier using a privately funded manned vehicle. The flight also served to validate a relatively cheap - roughly $20 million - suborbital launch capability for an embryonic space tourism industry seeking investors and customers.
But a mix of serious in-flight errors were considered a major setback and clearly dampened Rutan's post-flight exhilaration. Scaled Composites was expecting to announce plans to claim the X-Prize within days of the launch.
"There is no way we would fly again without knowing the cause and assuring that we would have fixed it," says Rutan, who had earlier described the 21 June launch as inherently less risky than a previous envelope expansion flight in May.
SpaceShipOne's glitches began a few seconds after separation from mothership White Knight at 50,000ft. As Melvill ignited an estimated 73-76s rocket burn, the vehicle unexpectedly rolled 90° left. Melvill corrected with a sharp rudder input, but the cause of the uncommanded manoeuvre was not immediately clear.
The performance of the SpaceDev-built rocket motor is uncertain. For the first time in four powered flights of SpaceShipOne, Rutan refused to provide timing data for how many seconds elapsed between rocket ignition and cut-off. Partly, he said, this was because he did not know how the motor turned off - either by Melvill, automatic shutdown or engine failure.
But it is certain Melvill's ascent ended prematurely. SpaceShipOne's flight profile and fuel load called for a climb-out to 360,000ft.
The flight also saw the first use of a 25:1 turndown ratio engine nozzle, upgraded from a 10:1 nozzle previously used. A carbonfibre fairing was added to reduce drag by about 4%, but the thin material shrouding the nozzle buckled during the flight. Melvill says that could be the source of two "bangs" heard during the ascent, possibly degrading engine performance.
STEPHEN TRIMBLE / MOJAVE
Source: Flight International
