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."
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