Turnaround Time

The twenty-nine rolls not only caused great concern for safety, but now doubt and skepticism started to creep into the back of people’s minds. One or two rolls wouldn’t have been so dramatic, and would not have left such a vivid impression. But with twenty-nine, even the most inexperienced spectator could tell things weren’t going as planned. The public had not yet bought into the whole idea of personal space travel. There was a big difference between being enthusiastic and thinking something was cool and being willing to put your own butt in the seat strapped to a rocket engine. Some people would of course be willing to take any risk to get into space. But that certainly wouldn’t be the best way to jumpstart an industry in this day and age. Sometimes perception, unfortunately, weighs heavier than fact.

“We saw this rolling departure, and that was cause for concern,” Binnie said. “Not from a safety or structural standpoint but a concern of perception. Others thought, ‘Well, they are just loose cannons out there. They don’t understand what they are doing. They are certainly not ready for prime time or carrying the trusting public.’ And so the clock is ticking.

“We had planned this to where we could potentially pull off three flights in two weeks if need be. But we were all getting kind of tired. We really didn’t want to have a problem on our second attempt. Everybody on the team was well aware of what was at stake and what would all be necessary should it have to come to a third flight. And any number of things could put us there. It could be bad weather, an avionics hiccup, range issues, telemetry things, and issues totally unrelated to flying the vehicle could have scuttled that event and forced us into a third evolution.”

The fact was that after evaluating the data from X1, the team determined Melvill had done too good of a job at pointing SpaceShipOne straight up. In this orientation, SpaceShipOne had no aerodynamic lift to correct unwanted motion. “You’ve got to be careful that you don’t go over on your back,” Melvill said. “It is real easy to pull so hard that you end up overturning.”

With the nose of SpaceShipOne pointed straight up, a degree or two off one way or the other was not much of a change in angle. But it turned out to be a tremendous change in terms of SpaceShipOne’s stability. So, when Melvill went beyond 90 degrees, he naturally tried to bring the nose back on track. This caused the angle of attack, the direction SpaceShipOne was pointing in relation to the direction of actual motion, to go to zero.

“The wing wasn’t lifting anymore, there was zero lift on the wing, then it departed,” Melvill explained. “It did a snap roll. And that was caused by the design of the airplane. The airplane was designed with a high wing and swept leading edge. Had that been a low wing, it would not have done what it did. We learned that lesson. On the next flight, we didn’t change the airplane at all. We just changed the pull – up schedule.”

The new plan for the trajectory was a more gradual pull-up during boost while making sure never to go to vertical. “And as

long as that wing is lifting, it won’t stall like that. But when it gets to zero lift, then you get separation on it, and the slightest little perturbation of airplane will cause it to roll or do something odd,” Melvill said.

None of the flights previous to XI had flown at high Mach numbers while at a zero angle of attack. Essentially, SpaceShipOne lost directional stability, so there was no way Melvill could counteract the weak thrust asymmetry, a wandering thrust line, coming from the rocket engine at the time. SpaceShipOne was still rocketing up, so by the time the first few rolls occurred, the atmosphere had disappeared. Aerodynamic forces were not longer causing the rolls, but since there was no air pressure to resist the rolling motion, once SpaceShipOne started to roll, it just kept going and going.

The structural loading on SpaceShipOne from the rolling was very low. Melvill’s safety was never in jeopardy, only his breakfast, which thanks to all of the unusual-attitude training in the Extra 300 aerobat­ic plane, remained in place. The very next day, Scaled Composites not only figured out what caused the rolling departure but also deter­mined a way to keep it from happening again.

As with the first rocket-powered launch of SpaceShipOne, Rutan wanted to fly on a significant day in aviation history. The anniversary of the first man-made object to orbit Earth was approaching. Russia’s Sputnik, as shown in figure 9.9, was launched on October 4, 1957, and circled Earth about 1,400 times at a peak apogee of 588 miles (947 kilometers). This milestone of spaceflight sent the space programs of the United States and the USSR into warp speed.

“We had three days to finesse this in the simulator,” Binnie said. “Between Mike’s flight and the final flight, it was Friday, Saturday, Sunday. It looked promising, but it was still only our sixth powered flight in the vehicle. There was no guarantee that we really under­stood it or that there weren’t some other gremlins that were going to leap out and get us.”