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Serendipitous background monitoring of the Hubble Space Telescope's Faint Object Spectrograph

John E. Fitch, Glenn Schneider, Pierre Y. Bely, James B. Breckinridge
1993 Space Astronomical Telescopes and Instruments II  
The nature of the Hubble Space Telescope's (HST) low Earth orbit imposes scheduling restrictions and interruptions in the data collection periods for it's compliment of scientific instruments. During many of these times the Faint Object Spectrograph (FOS) is in a full operational configuration and is taking detector background measurements which are continually reported in HSTs engineering telemetry stream. These data are primarily used to monitor the instrument for changes in behavior
more » ... n behavior resulting, principally, from intermittently noisy diodes in its digicon arrays. These same data may be used to monitor temporal changes in the charged particle environment of HSTs near-earth orbit. The FOS has its own microprocessor which controls observations. When a given observation ends, the microprocessor continues to accumulate data in the last commanded configuration, but no longer transfers and sums that data in its science data buffer. The FOS microprocessor does however, collect the accumulated data in a separate engineering buffer as a means of detecting excessive current draw on the photocathode. This so called 'Overlite' telemetry represents the summation of the counts from all the active diodes over the previous 60 seconds. During the times when the FOS is in a stable operate condition, and no photons are being collected from a target, the Overlite sum gives an accurate representation of the dark background for the detector during that minute. 214
doi:10.1117/12.158772 fatcat:jupixtrhe5ba3h3qzwrpyzgp4i