NASA's Terra Satellite Moved to Avoid Chinese ASAT Debris

by Brian Berger, Space News Staff Writer

Date: 06 July 2007 Time: 09:28 AM ET

This story was updated at 1:18 p.m. EDT.

WASHINGTON ? Flight controllers at NASA?s Goddard Space Flight Center, Greenbelt, Md., had to maneuver the Terra environmental spacecraft in late June to avoid orbital debris created by the Jan. 11 test of a? Chinese anti-satellite (A-Sat) weapon.

NASA officials said July 5 that the event marked the first time the agency has had to move one of its spacecraft to avoid a potential collision with debris created by the controversial Chinese A-Sat test.

A defunct Chinese weather satellite, Fengyun 1-C, was orbiting at an altitude of roughly 528 miles (850 kilometers) when it was destroyed Jan. 11 after being struck by a kinetic energy A-Sat weapon, producing a cloud of debris that is being tracked by the U.S. military?s Space Surveillance Network.

A ?Terra Mission Status Update? posted on the U.S. space agency?s Web site says Goddard flight controllers briefly fired Terra?s thrusters June 22 after a week of tracking and analysis showed a 7-percent chance of the satellite being hit by Fengyun-1C debris the following day. The maneuver boosted Terra by 0.8 miles (1.3 kilometers) and reduced the chance of collision to zero, the status report says.

Lauri Newman, Goddard?s conjunction assessment manager for the agency?s Earth science satellite constellation, said an orbital debris report she received from the U.S. Air Force June 18 showed that a single piece of Fengyun-1C debris measuring about 15 inches (40 centimeters) across was on course for a possible collision with Terra later during that week.

?We found the event on a Monday during routine analysis and did the maneuver on Friday,? she said.

Because of the advanced warning, NASA only had to fire Terra?s engine for a relatively short 1.3 second burst to move the satellite out of harm?s way. The resulting momentum raised Terra?s orbit by 0.8 miles over the next 24 hours.

NASA typically fires Terra?s engine three to five times a year for about eight seconds at a time to compensate for normal atmospheric drag.

NASA does not know for sure whether the Fengyun-1C debris would have hit Terra if it had not been moved out of the way. But subsequent analysis, Newman said, showed that a collision was still possible.

?We got one final prediction after we did the maneuver and that showed that it was still in the error bands that we were showing before,? she said.

Asked if she considered the June debris event a close call, Newman said, ?from what we?ve seen so far, yes.?