By Joel Achenbach
Washington Post Staff Writer
Friday, March 13, 2009
Part of an old rocket motor threatened to collide yesterday with the international space station, forcing three astronauts to take refuge in an attached Russian spacecraft that serves as an emergency lifeboat.
No collision occurred, and the evacuation of the station lasted only 11 minutes. But the unusual event offered a reminder that astronauts and spacecraft are increasingly playing a nerve-jangling game of space-debris dodge ball.
The speeding object, about five inches in diameter, was a motor component that had been circling Earth since the 1993 launch of a Navy global positioning system satellite, said NASA orbital debris program manager Eugene G. Stansbery.
Although the U.S. Strategic Command (STRATCOM) tracks about 19,000 objects, including dead satellites, rocket boosters, and debris from space collisions, the motor component is quirky, with a highly elliptical orbit that ranges 2,485 miles above Earth to 89 miles. At the lowest point of that orbit, the object scrapes the atmosphere and slows down, making its future trajectory harder to predict with precision.
STRATCOM notified NASA officials late Wednesday that there would be a "conjunction" -- a potential collision -- at 12:39 p.m. EDT yesterday. The object was projected to miss the station by a little less than three miles, too close for NASA's comfort, given the inherent uncertainties in tracking orbital debris.
Typically, the flight team at NASA has three or four days' warning of a conjunction, enough time to maneuver the space station, currently 217 miles above Earth, out of harm's way. In this case, according to NASA, there wasn't enough time to plan and execute an avoidance maneuver.
The three astronauts -- two Americans, Mike Fincke and Sandra Magnus, and a Russian, Yury Lonchakov -- were not told of the situation until 11:40 a.m. EDT, about an hour before the conjunction, just as they were waking up. Capsule communicator Kathryn Bolt, speaking from Mission Control at the Johnson Space Center, told space station commander Fincke of the change in plans for the day.
"We have information about a red conjunction; the information came in late, and with the uncertainty of it, we are wanting to take a conservative approach," she told Fincke. She said there was low probability of a collision but then reeled off the protocol for putting the space station in unmanned mode and taking refuge in the Soyuz.
"So, you want us to execute this right now?" Fincke asked.
"Mike, that is correct," Bolt said.
The astronauts entered the Soyuz spacecraft at 12:35 p.m. Ten minutes later, they had the all-clear -- the object "has passed with no impact. . . . great news," Bolt said -- and they returned to the station.
Space debris drew headlines last month when two satellites collided 491 miles above Earth. Hundreds of fragments are now dispersed in two debris trails that completely circle Earth.
The impact of even a very small object moving at orbital velocity could be catastrophic to the space station. The motor component zoomed past the station Thursday at more than 21,000 mph. How close it came to a direct impact remains unknown.
"The folks at the U.S. STRATCOM were unable to get a good lock on it because it was so small," NASA spokesman Kelly Humphries said. "We probably will never know how close it came."