The HEAO-A Scanning Modulation Collimator Instrument

The Scanning Modulation Collimator X-ray instrument for the HEAO-A satellite was designed to measure celestial radiation in the range between 1 and 15 KeV and to resolve, and correlate, the position of X-ray sources with visible light sources on the celestial sphere to within 5 arc seconds. The positional accuracy is made possible by mechanical collimation of the X-ray sources viewed by the instrument. High sensitivity is provided from two systems each containing four gas fllled proporticnal counters followed by preamplification, signal summing, pulse height analysis, pulse shape discrimination, X-ray event accumulators and telemetry processing electronics.