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39.2 Instrument Capabilities and Design

The HSP had five detectors: four image dissector tubes and one photomultiplier tube (PMT). There were two image dissectors with photocathodes sensitive to visual wavelengths (VIS and POL) and two sensitive to the near UV (UV1 and UV2). There were no moving parts in the HSP because the target star was positioned in the desired aperture filter combination (each detector had many filters and apertures) by moving the telescope. A particular aperture was sampled by the detector read beam which was positioned by deflection coils in the detector assembly.

The HSP was designed to obtain high speed photometry with the VIS, UV1, and UV2 detectors in any one of the following modes:

Single color photometry.
Star-sky photometry.
Prism. The HSP could also be used in the SPLIT mode. In SPLIT mode, simultaneous observations were done using the PMT and the VIS detectors. A complete description of the HSP and its method of operation was given by Bless et al. (1992) as updated by Bless et al. (1997).
The HSP collected two types of data: digital and analog. Digital data consisted of the count of pulses from a pulse amplitude discriminator for a time equal to the integration time. Analog data was the output of the 12-bit analog-to-digital (A/D) converter. Analog data always produced two bytes of data. There were three science data collection modes:
Single color photometry.
Star-sky photometry using one or two detectors.
Area scans. Additional detailed information is in the final version of the HSP Instrument Handbook.

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