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Proceedings Paper

Test Results And In-Orbit Operation Of The Infrared Astronomical Satellite Circumvention Circuit
Author(s): E C Long; D Langford
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Paper Abstract

The Infrared Astronomical Satellite (IRAS) is a satellite which is mapping the celestial sphere for infrared (IR) sources. One of the critical electronic circuits in the instrument is the circumvention circuit which eliminates the unwanted charged particle pulses from the IR signal. The circumvention circuit was designed to allow IRAS to function throughout its orbit and into part of the South Atlantic Anomaly (SAA), through most of the north and south polar horns, and in the presence of cosmic x-rays. This paper describes the operation of the circumvention circuit along with preflight and in-orbit testing. Ground testing of the brassboard circuit, using a simulated preamplifier output, showed the circuit would perform the circumvention function as designed. The initial testing of the IRAS flight circumvention, circuit and remaining electronics was done using ten prototype detectors and preamplifiers. This testing showed that the system noise exceeded the 0.5 millivolt detection threshold set for the circumvention circuit. Increasing the threshold to 2 millivolts was the only change required to the flight circumvention circuit. When all the flight detectors and preamplifiers became available the circuit was tested using a gamma source to simulate charged particle sources. With the low energy deposited in the detectors (20 keV average) the noise was reduced by up to 5 times with the circumvention circuit turned on. In-orbit results show the circumvention circuit decreases the unwanted charged particle background noise up to two orders of magnitude. The difference in the results with the circumvention off and on are so great that the science team has recommended that no data be taken with the circumvention circuit off. Figures are presented showing in-flight results with and without the circumvention circuit.

Paper Details

Date Published: 9 January 1984
PDF: 8 pages
Proc. SPIE 0445, Instrumentation in Astronomy V, (9 January 1984); doi: 10.1117/12.966156
Show Author Affiliations
E C Long, Ball Aerospace Systems Division (United States)
D Langford, Jet Propulsion Laboratory (United States)

Published in SPIE Proceedings Vol. 0445:
Instrumentation in Astronomy V
Alec Boksenberg; David L. Crawford, Editor(s)

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