MOJAVE, California -- The first X Prize flight of SpaceShipOne prompted concern on the ground Wednesday morning -- followed quickly by rumors in the news and on the Internet -- as observers watched the rocketplane repeatedly roll as it sped toward the fringes of space.
However, in an e-mail message to reporters Friday, Burt Rutan, the spacecraft's chief designer addressed what he described as a number of "incorrect rumors about the rolls," and offered an account of what took place as pilot Mike Melvill sped to high altitude above Earth.
"The complex reason on why the rolling departure occurred will be described in a report we will post at a later date," Rutan wrote reporters.
Extremities of the atmosphere
The first roll of SpaceShipOne occurred at a high true speed, about Mach 2.7 (2.7 times the speed of sound), Rutan advised. The aerodynamic loads on the vessel were quite low and were decreasing rapidly, "so the ship never saw any significant structural stresses."
"The reason that there were so many rolls was because shortly after they started, Mike was approaching the extremities of the atmosphere," Rutan stated. Nearly all of the 29 rolls were done in continuous fashion without aerodynamic damping -- as opposed to how an aerobatic airplane performs rolls at a much lower altitude and within a much thicker atmosphere.
"In other words, they were more like space flight than they were like airplane flight. Thus, Mike could not damp the motions with his aerodynamic flight controls," Rutan said.
Time to relax
Rutan said that pilot Melvill elected to wait until he feathered the boom-tail in space -- a large tail section of the craft used to slow down during reentry -- before using the reaction control system thrusters (RCS) to take out the roll rate of the vehicle.
"When he finally started to damp the rates he did so successfully and promptly. The RCS damping, to a stable attitude without significant angular rates was complete well before the ship reached apogee (337,600 feet, or 103 kilometers)," Rutan stated.
"That gave Mike time to relax, note his peak altitude, and then pick up a digital high-resolution camera and take some great photos out the windows. Those photos are now being considered for publication by a major magazine," Rutan added.
"While we did not plan the rolls, we did get valuable engineering data on how well our RCS system works in space to damp high angular rates," Rutan said. "We also got a further evaluation of our 'Care-free Reentry' capability, under a challenging test condition."
Videos of the flight clearly show that the SpaceShipOne righted itself quickly and accurately without pilot input as it fell straight into the atmosphere, Rutan said. No other winged, horizontal-landing spaceship -- the X-15, the Russian Buran, nor the Space Shuttle -- has this capability, he said.
The report that Melvill defied a ground request to shut down the motor and let it run a few more seconds in order to reach the 100 kilometer altitude is not true, Rutan advised.
"While a Mission Control aerodynamist did discuss a possible abort a few seconds earlier, Mike immediately shut down the motor on the first advisory call over the radio. Mike himself was monitoring the apogee predictor during the initial rolls and was in the process of going for the thrust termination switch as he heard the advisory call," Rutan said.
No maintenance squawks
Meanwhile, work is underway at the Mojave Spaceport in readying SpaceShipOne for Monday's X2 flight - the second of the two space shots required to win the $10 million Ansari X Prize.
A full inspection of the vessel after its X1 flight last week has been completed, Rutan told SPACE.com, with no problems in readying the craft for another rendezvous with history.
"Absolutely no maintenance squawks on the ship," Rutan said. "The new motor and passenger ballast was installed yesterday. We mate today [with the White Knight carrier plane] and load oxidizer Sunday."
Target time for rolling down the runway is 6:30 AM local time Monday.
"It actually could be done faster if we had to," Rutan said.
- X Prize and SpaceShipOne: Full Coverage