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Based on information from "HEAO-1 A-2 Experiment: The Configuration of
the Hard X-ray Detectors" F.E. Marshall 1983.
The HEAO-1 spacecraft was launched on 12 August, 1977 (day 244 of
1977). The first week of operation was devoted to turning the
detectors on and to calibrating their performance. The detectors
gradually achieved long-term stability. On day 232.04, the detectors'
high voltage was changed to their normal state, where it remained for
the rest of the mission. Stability was achieved for the HEDs at day
234.95; MED stability was achieved at 248.15.
Changes during the Mission
From Day 233.01 to Day 233.09, events in Window 1B were not
processed by any of the HEDs as a calibration.
From Day 234.03 to Day 234.53, the bit to identify in which layer
the X-ray occurred was dropped and the least significant bit of the
pulse height was included for all detectors. After day 304.93, the
same processing occurred for all detectors except HED 2.
From Day 235.63 to 245.69, the MED did not process events in
Window 2B because the PHA Window Layer 2 was inadvertently changed to
not include Window 2B.
From Day 432 the LED heaters were on part of the time to increase
the temperature of the LEDs. However, there was a sharp increase in
temperature of all the detectors.
From Day 510 the heater in the gas system was on part of the time
to increase the temperatures of the HEDs and the MED. After Day 510
the temperatures were less stable.
From Day 645 until the end of the mission, HED 2 and HED 3
included only Layer 2 in the multiscalar rates.