Ariel V was launched into a low inclination (2.8 degrees) orbit from the
San Marco launch platform in the Indian Ocean on 15 October 1974. The
satellite was placed in a nearly circular orbit with an altitude of ~520 km,
had a nominal spin period of 6 s, and had an orbital period of ~100 min. The
on-board experiments were operational only during the sunlit portion of the
orbit, typically 60-min in duration. The satellite re-entered the Earth's
atmosphere on 14 March, 1980.
The Ariel V satellite monitored the X-ray sky with 6 different instruments.
Four of the instruments were aligned with the spin axis: a Rotation Modulation
Collimator (RMC), operating in the energy range 0.3-20 keV and capable of
determining source positions to ~2 arcmin; a high resolution proportional
counter spectrometer, with 128 channel pulse height analyzer over the range
2-30 keV; a polarimeter/spectrometer, operating in the range 2-8 keV and
capable of detecting polarization of 3%; and a Scintillation Telescope (ST),
devoted to temporal and spectral studies of sources at energies upto 40 keV.
While these 4 experiments were devoted to a detailed study of a small region of
the sky within ~10 degrees of the satellite pole, the 2 other experiments
covered wide regions of the sky. These 2 experiments were the All-Sky Monitor
(ASM) and the Sky Survey Instrument (SSI). The ASM provided coverage in the
range 3-6 keV with a pair of ~1 cm2 each pinhole cameras. It viewed
the entire sky with the exception of an ~8 degree wide band centered on the
spacecraft's South Pole. It was intended as an early detection system for
transient events, and as a continuous monitor of relatively bright (> 0.2 Crab)
galactic sources. The SSI consisted of two pairs of proportional counters (LE
system and HE system) each having an effective area of 290 cm2. Due
to a slow post-launch leak, one LE detector was switched off early in the
mission, reducing the effective area of that system to 145 cm2.
The detectors were located in the spacecraft's equatorial region and scanned a
20 X 360 degree wide band of the sky every satellite spin. The two systems had
a 1.2-5.8 keV (LE) and 2.4-19.8 keV (HE) energy range. Each pair of detectors
had a field of view collimated to 0.75 X 10.6 degrees (FWHM). The SSI primary
science goals were to conduct a high-sensitivity survey of the sky and obtain
locations, intensities, and spectra of interesting sources.