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Mission Status Report #82      Star Date: February 23, 2005

Progress Toward Recovery

Background info on Reaction Wheel Anomaly. (Jan. 7, 2005.)

The FUSE spacecraft remains in a safe and stable attitude while corrective measures are taken to allow the resumption of science operations. As reported last month, this safe configuration has FUSE essentially pointing straight "down" (toward the center of the earth) as it orbits, rather than pointing "inertially" (at a single spot on the celestial sphere) as would be done for science operations. In this configuration, there are almost no disturbances on the spacecraft from "gravity gradient" torques, and so it remains stable. Sufficient charging on the solar panels occurs on each day pass to keep the batteries charged.

Significant progress is being made on a revised control alogorithm that should allow a resumption of science operations in the near future. Tests and simulations in the laboratory indicate the new algorithm can provide three-axis controlled sub-arcsecond pointing, as needed for science operations, at least in favorable attitudes on the sky with respect to attitude disturbances and magnetic field orientation. When testing is complete, we will upload the flight software patch, and then cautiously try to bring the satellite back online for testing. This will be a days-long process, as the satellite is returned to inertial pointing mode, carefully warmed up to operating temperature, and thermalized. Then the front doors will be opened, and the detector high voltages will be brought up slowly for the first time since late December. We will be back to limited science operations.

Initially, we will stay close to the northern continuous viewing zone (close to the orbit pole) and make a restricted set of observations while we test out the new pointing system. Then we will "learn as we go," trying more sophisticated maneuvers and pushing the envelope to verify our stability simulators and planning software and learn how to operate in this new mode. This closely parallels what happened back in 2001 as we first came online again in two-wheel mode. We have a lot of learning to do, but we are optimistic about our chances of returning FUSE to science operations!

I will post further updates as they are warranted. Stay tuned.

Reported by: Bill Blair, FUSE Chief of Observatory Operations

Last Update: February 15, 2005

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