Rutan explains SpaceShipOne rolls
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: October 2, 2004
Burt Rutan, designer of SpaceShipOne, said in a website posting Saturday that more than two dozen rolls experienced by pilot Mike Melvill during last week's Ansari X Prize flight occurred in what amounted to a space environment and that the vehicle was never in any danger.
Melvill flew SpaceShipOne to an altitude of 337,600 feet - 63.9 miles - last Wednesday in the first of two flights needed to win the $10 million X Prize, which goes to the first team to build and launch a commercial spacecraft into suborbital space twice in two weeks. Rutan plans to send SpaceShipOne aloft on its second X Prize flight Monday morning. The identity of the pilot has not yet been announced.
Fifty seconds or so into powered flight last week, SpaceShipOne began rolling about its vertical axis, alarming reporters on the ground who feared the craft was out of control. Even the official commentators discussing the flight on an X Prize webcast expressed alarm.
But Melvill stopped the roll as the ship climbed out of the atmosphere and he completed a flawless re-entry and landing. It was reported at the time that flight controllers had ordered Melvill to shut down the craft's engine and that the pilot delayed long enough to ensure he reached the minimum 100-kilometer altitude required by the X Prize competition.
Not true, said Rutan. Here is the text of his explanation:
"The complex reason on why the rolling departure occurred will be described in a report we will post at a later date. What I am intending to do here is merely address some of the incorrect rumors about the rolls that have been seen in various news stories and web discussion groups.
"While the first roll occurred at a high true speed, about 2.7 Mach, the aerodynamic loads were quite low (120 knots equivalent airspeed) 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. Nearly all of the 29 rolls that followed the initial departure were basically at near-zero-q, thus they were a continuous rolling motion without aerodynamic damping, rather than the airplane-like aerodynamic rolls seen by an aerobatic airplane. 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.
"Mike elected to wait until he feathered the boom-tail in space, before using the reaction control system thrusters (RCS) to damp the roll rate. 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 Km). 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.
"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. We also got a further evaluation of our Care-free Reentry capability, under a challenging test condition. As seen on the videos of the flight, the ship righted itself quickly and accurately without pilot input as it fell straight into the atmosphere. No other winged, horizontal-landing spaceship (X-15, Buran, Space Shuttle) has this capability.
"Some publications have stated that Mike defied a request to shut down the motor and let it run a few more seconds in order to reach 100 Km altitude. This is not true. 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."