Mission Status Report #15 Star Date: August 23, 1999
NOTE: Mission Status Reports on the web page will continue roughly once a week, as events unfold.
The Satellite Control Center at JHU.
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Checkout Progress Slowed by Solar Activity
The last week has seen continued progress on FUSE checkout activities, but at a slower pace, due to some difficulties both on the satellite and ground support system. In particular, it appears that at least some of these problems may have been triggered by high solar activity and an ensuing (but temporary) change in the radiation environment of the satellite.
Certain electronic components in FUSE are sensitive to the influx of high energy particles. One of these areas is the computer memory of the detectors in the spectrographs. The control software is run in two redundant areas of memory (let's call them "upper" and "lower" memory), so that if a particle event (called a "single event upset", or SEU) is detected in (say) upper memory, we can switch to lower memory, and vice versa, with no operational impact. The occurence of SEUs is typically one per 5 days or so, and so the chances of getting an SEU in both upper and lower memory in the same time period on the same detector is very low. Well, you guessed it--it happened early last week, and furthermore, it happened to the detector we had fully ramped up and were using for testing! Analysis after the fact showed that the solar X-ray flux had increased by a factor of 100, implicating high solar activity as the probable culprit.
Our protocol for this situation is to turn off the affected detector, turn it back on, reload the memory areas again, and then continue. We also had to ramp the high voltage back up to operating values, which takes a full day. We are now back up and operating normally.
Another unexpected problem cropped up late in the week, when we lost functionality in our primary ground station antenna at the University of Puerto Rico Mayaguez. A fire at a power sub-station in Mayaguez terminated power to the antenna and support equipment. The backup generator carried things for awhile, but when the power was not restored in time, the site lost power entirely. When power was restored, the system did not boot back up properly, possibly indicating a hardware problem. (This is still being diagnosed.) Thus. continued operations have been occurring through the commercial Hawaii station of Universal Spacenet.
Despite these difficulties, progress was made this week. We have taken numerous "background" exposures with the detector and seen airglow lines (emission from the residual atmosphere above FUSE). We have run tests that have shown the relative pointing positions of the two separate telescope mirrors that use detector 1. (This is basically a practice run for what will have to be done to get all four mirrors aligned.) And we have performed a successful "gyro calibration" which should help in smoothing out future target acquisitions.
We still expect to be able to ramp up the high voltage on detector 2 this week, depending somewhat on the situation at the Puerto Rico ground station. With both detectors ramped up, we can then begin the process of alignment and focus of all four telescopes!
It is important to note that, while many problems have been encountered during checkout,, they are of the annoying "slow-you-down" kind. The satellite is healthy, and the hardware is working! It just takes time.
Reported by: Bill Blair, Chief of Mission Planning
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