FUSE Mission Status Report

Mission Status Report #9      Star Date: July 8, 1999

Photo: FUSE soars up into the heavens aboard the Delta II rocket. (Photo: B-G Andersson)

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Mission Status Reports on the web page will occur when news-worthy events occur (but at least weekly!) for the time being.

-- Bill Blair


The FUSE satellite remains healthy and the In-Orbit Checkout phase is still in progress. The Satellite Control Center at JHU is routinely in contact with the spacecraft through the Puerto Rico and Hawaii ground stations, and occasionally through TDRSS contacts. Thermal control has been thoroughly tested, with the spectrograph ready for "bake-out" mode prior to reducing temperatures as we approach normal operations.

The Ops team has been exercised by several issues, some of which are still being worked at this writing. During the weekend, some anomalous behavior was detected in the telemetry at several different times; careful analysis after the fact of the timing of these incidents showed a direct correlation with passages through the highest background regions of the South Atlantic Anomaly (SAA), a portion of the orbit that intercepts the earth's radiation belts. Since this behavior have not repeated on SAA passes since the weekend, it is hoped that these were "unlucky" events, possibly related to the increased solar activity at that time, and not an on-going problem. Still, analyzing such occurences with a new satellite takes time and effort, and has helped to push the checkout behind our nominal pre-launch schedule. On the plus side, the behavior of the Fine Error Sensor CCD cameras in passing through the SAA has been characterized, and it looks like we should be able to maintain tracking of guide stars without loss of lock.

Another area being worked involves the Attitude Control System (ACS). The spacecraft uses a combination of onboard information and data uplinked from the ground to understand exactly where it is in its orbit at any given time. While this can nominally be calculated with accuracy, small changes in the orbit parameters occur due to variations in atmospheric drag and other second-order effects. If the ACS thinks the information it has and the information uplinked from the ground are incompatible (over some threshold), it basically says "I don't like this!" and puts the spacecraft into a "Safe Pointing Mode" until ground controllers analyze the situation. Such an event happened over the holiday weekend, and since this is the first such occurrence of the FUSE mission, it is being thoroughly analyzed before we proceed. (Since the telescope doors are still closed, there is no safety concern.)

Not all checkout activities involve specific spacecraft pointing orientation, and so the ordering of checkout events has been shuffled somewhat to continue to make forward progress. The planning team has responded well to these "replan" cycles, and operations continue to run smoothly.

Over the next week, we hope to proceed to opening one telescope door and taking our first test images of the sky with the FES guide camera. This will allow the telescope focus to be assessed and permit our first attempts to actually guide on stars. However, the FUV spectrograph detectors will still remain at low voltage until the telescope structure has more time to outgas in the near-vacuum of space.

Reported by: Bill Blair, Chief of Mission Planning

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