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Updated 07 July 2007:
The instrument far-ultraviolet (FUV) detector resumed full operation in early July 2006. All parameters are nominal and the detector is now operating for the normal time of 25 to 30 minutes per orbit. There is no indication of any damage to the FUV detector or change to the detector response.
The near-ultraviolet (NUV) detector operation continues to be nominal.
Background:
On March 30, 2006, the far-ultraviolet (FUV) detector high voltage was turned off when the on-board fault protection noted an overcurrent from the high voltage power supply. Testing at low voltage indicated a similar anomaly to the one in March 2005, which we believe was caused by a short in one micro-channel-plate (possibly caused by microscopic debris). We recovered from the March 2005 by on-off cycling of the voltage at gradually increasing voltage levels; this effectively "hi-pots" the problem area (burns off or wears down the debris by repeated hi-voltage pulses).
Software changes implemented since spring 2005 allowed us to bring the detector back to nearly full science-ops voltage during the first two weeks of April. However, the FUV then began to experience excess charge accumulation (possibly as a result of operating on the orbit dayside too much), and it began to experience more overcurrents (apparently from the incomplete smoothing down of the defect). Voltage cycling was restarted from a lower level, and proceeded with much longer "stays" at each voltage level until operating levels were reached.
Implications:
GALEX missed observing during the months of April-June for two years sequentially, and is still recovering targets missed in the time July-September 2005. However, we anticipate (knock on wood) recovery from the backlog by the end of calendar year 2007, and thus no particularly oversubscribed regions for calendar year 2008.
Responsible NASA Official:
Curator: