After a little less than three months, SpaceShipOne was ready to return to the air again, with Pete Siebold at the controls. However, its rocket engine would be quiet during this test flight.
“It was after the famous 11P flight, which resulted in significant damage to the aircraft on the hard landing,” Siebold recalled. “It was
in one respect what we would call a functional check flight after any major modifications to the airplane. We wanted to go fly it in a semi – benign environment and try and shake down any of the problems that we may have overlooked or additional problems that had been created due to the modifications.
“The other reason was we made some modifications to the aerodynamic shape. We added the thermal protection to the aircraft. If you look at the artwork of that flight, it shows the red leading edges and shows the TPS addition. That actually changed the wing shape slightly and the aerodynamic shape. So, we wanted to go and fly that and see if there were any ill effects to that modification for the flight.”
Siebold started off his second time flying SpaceShipOne at an altitude of 48,500 feet (14,780 meters), which was the highest point that White Knight ever released SpaceShipOne. Scaled Composites had originally planned on releasing SpaceShipOne from an altitude of 50,000 feet (15,240 meters). However, White Knight had a very difficult time flying this high and too frequently had come out of afterburners or flamed out altogether at an altitude even below this one. The lower launch altitude did actually work in SpaceShipOne’s favor.
During powered flight, the first thing that SpaceShipOne had to do was “turn the corner” as soon as it possibly could, but the higher the altitude, the less air there was for the wings to bite into in order to make a quick turn upward. So, in terms of utilizing the energy from the rocket engine as efficiently as possible, launching below 48,000 (14,630 meters) feet gave better overall performance, since SpaceShipOne would spend more time pointing up than over.
However, since Siebold wasn’t concerned with lighting off the rocket, he wanted all the altitude he could get for the glide flight. “There were some minor glitches,” he said. “The thermal protection system started cracking at low temperatures, and I think there was actually a formulation change made between that flight and the actual powered flight.”
But the thermal protection system (TPS) wasn’t the only system being checked out. Siebold also evaluated the reaction control system (RCS) that would be used to maneuver SpaceShipOne while in the absence of the atmosphere. This and other testing worked out smoothly, and SpaceShipOne touched down safely, even in the presence of a strong crosswind.