Caption: Graphic showing how FUSE might look on-orbit. The telescopes are looking toward the upper right in this picture, and only two of the four telescope doors are visible from this angle. The blue rectangles represent the solar panels, which connect to the spacecraft at the bottom. (Figure courtesy NASA and the FUSE project.)

The FUSE spacecraft experienced a significant anomaly May 8, 2007, involving the skew reaction wheel. See earlier status reports for details.

Several significant steps have occurred since my last report. Firstly, we have had the wheel spinning two more times, although for briefer periods than the initial restart described in my last report. These tests permitted us to assess ways we might control the satellite in a power-positive attitude while keeping the wheel spinning. Also, we have had time to study telemetry both from the time period leading up to the anomaly and from the restart periods. This analysis confirms the presence of excess friction on the wheel, and eliminates an electronic problem as the cause of the anomaly. Plans are now underway for additional wheel restart attempts, taking what has been learned into account.

Data from the week or two prior to the wheel problem is quite interesting. While there was evidence in the telemetry from this period for increased friction on the wheel, the pointing performance was unchanged, and the science data acquired during this period appears nominal. Hence, this provides hope that we might be able to bring the satellite back into service, so long as the wheel performance does not degrade further. But there are no guarantees.

I want to express my continued thanks to the many people who are putting in long hours to keep FUSE safe during this difficult period, and who are helping us troubleshoot the problem. I have said this before during our previous anomalies with FUSE: it is amazing to experience firsthand the creativity and problem solving skills of these incredibly technical people as they work to first understand and then attempt to resolve a problem. Let's just hope they have one more rabbit to pull out of the hat.

We request the continued patience of the community while we perform further tests to understand the wheel's performance and adjust our plans accordingly. More information will be provided here, electronically to the FUSE users mailing list, and through the NASA project scientist's office at NASA/Goddard as the information becomes available.

For background on reaction wheels, see this report from an earlier wheel problem on FUSE from Jan. 2005.

Reported by: Bill Blair, FUSE Chief of Observatory Operations

Last Update: May 24, 2007

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