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Power Lunch In The Action Room

August 5, 1999 ::

CXC's orbit - artist illustration
Illustration of Chandra's Integral Propulsion System (IPS) making two burns at perigee and three at apogee to raise and finalize the orbit. Intermediate orbits after the IPS-3 and -4 burns are not shown.
Illustration: NASA/NGST
For five very quiet minutes during the lunch hour yesterday, Chandra officials huddled anxiously around computer monitors in the Action Room. They watched colored indicators as the two redundant rocket engines of the Inertial Propulsion System (IPS) fired for the first time. No red lights flashed to warn that the engines were getting too hot and when they cut off at 12:41 p.m. EDT, there was a palpable sense of relief in the room.

Chandra orbit path
View orbit animations. Illustration: NGST
Chandra managers had decided, after reviewing the performance of the third IPS burn to switch to the back-up engines. There were some faulty temperature sensors on the original pair and one of the engines was not performing quite up to par. Although there was some feeling that they should continue to use the engines that had already been proven, it was ultimately considered prudent to go with the new, redundant engines. The choice proved to be a good one.

"It's great to have that one out of the way," said Roger Brissenden, Chandra Center manager. "I didn't expect anything to go wrong, but you never know. We were using different engines with different flow rates and different thrusts."

The burn raised Chandra's perigee (closest approach to Earth) to 3,535 miles (5,689 kilometers) and left the apogee, or high point essentially unchanged at 86,448 miles (139,125 kilometers). Now the observatory is set for its next firing on Saturday, August 6 which should raise Chandra's orbit to its planned perigee.

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