Astronomische Nederlandse Satelliet (ANS)

photo of ANS in clean room

* Mission Overview

The Astronomische Nederlandse Satelliet (ANS) was a collaborative effort between the Netherlands and USA. The spacecraft was built by the Industrial Consortium Astronomical Netheralands Satellite (Fokker-VFW and Philips) and it was lauched on an American Scout rocket. ANS was launched from the Western Test Range, California, on August 30 1974 into a high inclination (97.6 degrees), sun-synchronous orbit. Due to a first-stage guidance failure the desired 500 km circular orbit was not obtained. Instead the satellite was placed in a elliptical orbit (initial perigee at 280 km and apogee at 1150 km period 98.2 minutes) that caused initial problems with the background radiation and complicated the scheduling of the obsevations. The spacecraft was a three-axis stabilized with one axis always pointed to the Sun (Z-axis). The experiments were mounted perpendicular to the Sun line (X-axis) and the spacecraft could be pointed, with an accuracy of 1 arcminute, towards any position in the sky perpendicular to the sun-axis. In 6 months, ANS made a complete circle in the sky. The satellite contacted the ground station once every 12 hours. The observing time was divided equally between the experiments on a one-orbit-per experiment basis. Typical data acquisition on a known point source consisted of the detector pointing either at the source continuously for ~1000 s, or pointing at the source for ~128 s, then pointing off for background accumulation. ANS was operational for one and a half year and the spacecraft re-entered in the Earth atmosphere June 14 1977.

* Instrumentation

The scientific payload consisted of an UV-spectrophotometer from the University of Groningen (15000Å-3300Å) and two X-ray experiments one from the University of Utrect (SXX; 0.16-7 keV) and the other from AS&E/MIT (HXX; 1.5-10 keV).
  • The Soft X-Ray Experiment (SXX) consisted of 2 parts. The Utrecht soft X-ray detetcor, sensitive from 0.2-0.28 keV, consisted of a grazing-incidence parabolic collector (effective arae of 144 cm2) with a small-area 3.6 micro polypropylene proportional counter in the focal plane. The sensitivity was such that 1 count/s (0.2-0.28 keV) was about 0.53 photons/cm2/s/keV at 0.28 keV. The second part, known as the Utrecht medium X-ray detector, was a proportional counter with a 1.7micro titanium window. It was sensitive in the 1-7 keV band, divided in 5 pulse-height channels, and an effective area of 45 cm2.
  • Hard X-Ray Experiment (HXX). The HXX also consisted of 2 major parts: the large area detector (LAD) and the Bragg Crystal Assembly (BCA). The LAD was a pair of narrowly collimated proportional counters sensitive to the energy range 1.5-30 keV, with a total area of 60 sq-cm. Each counter in the pair was collimated by 10' x 3 degrees. There was a 4' offset between the pair in the narrow direction. The LAD energy data from 1-30 keV were distribute over 15 pulse height channels and recorded with a resolution of either 4 and 64 seconds. A single channel collecting data from 1-7 keV could be read out every 1 or 4 or 16 sec. High time resolution (uo to a 1 ms) was also available. One ANS HXX count in the 1.5-7 keV was equivalent to 15 Uhuru counts. The Bragg Crystal Assembly is a pair of PET crystals and proportional counters aligned to search for silicon emission lines near 2 keV.

    * Science

    ANS made three important discoveries: detection of the first coronal emission from Capella, the detection of X-ray flares from the flares stars UV Ceti and YZ CMi and the discovery (along with Vela5A and 5b) of X-ray bursts. The first X-ray burst event was detected from the globular cluster NGC 6624 .
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