Photograph of ALEXIS in the clean room

* Mission Overview

The AstroSat mission is the first dedicated Indian asrtonomy mission. It is equpped with instruments to observe over a wide span of the electromagnetic spectrum, including visual, near and far ultraviolet, and X-ray wavelengths. The satellite was launched on September 28, 2015 from the Satish Dhawan Space Centre, in Sriharikota, India. AstroSat was placed in a 650 km altitude orbit with a 6 degree equatorial inclination. First light occured in early October, 2015. The initial mission plan calls for a five year duration, which is likely to be extended.

* Instrumentation

AstroSat carries several astrophysics instruments from ultraviolet to hard X-ray wavelengths. These include:

  • The Ultraviolet Imaging Telescope (UVIT), a pair of twin telescopes covering wavelengths 350–600 nm (near UV and optical) and 130–300 nm (far UV)
  • Large Area Xenon Proportional Counter (LAXPC), a trio of proportional counters for hard X-rays in the energy range of 3–100 keV. The combined counters provide an effective area of 8000 cm2 at 10 keV.
  • Soft X-Ray Telescope (SXT) for soft X-rays in the energy range 0.3–10 keV. SXT has a set of conical foil mirrors and a CCD detector with an effective area of 120 cm2 at 1 keV. The CCD array is thermal-electrically cooled to -80°C.
  • Cadmium-Zinc-Telluride Imager (CZTI) for hard X-rays in the energy range 10–100 keV. CZTI has a 6° field of view and a 490 cm2 effective area below 100 keV. The top of the instrument is covered by a Tantalum plate with a coded aperature mask, allowing image reconstruction from the shading pattern. The detector has four quadrants with 16 pixels in each quadrant, with each pixel having a cross-section of 2.5 mm x 2.5 mm, with timing accuracy of 20 microseconds. The detector elements are made of CdZnTe with a spectral accuracy of 0.5 keV (5%) at 10 keV.
  • Scanning Sky Monitor (SSM) for survey of sky in the energy range 2–10 keV. The SSM instrument uses a set of three one-dimensional position-senstive proportional counters equipped with coded masks. SSM is mounted on a single platform capable of being rotated to provide different orientations.
  • Charge Particle Monitor (CPM) to detect high energy particles, putting instruments in a temporary safe hold in event of extreme radiation. Although AstroSat’s low inclination orbit avoids the most intense areas of the South Atlantic Anomaly, the satellite does encounter the SAA: CPM monitors to ramp down high voltage systems to prevent instrument damage

* Science

AstroSat is performing simultaneous multi-wavelength monitoring of intensity variations for a broad range of cosmic sources. This includes monitoring the X-ray sky for new transient sources, performing sky surveys in hard X-ray and UV wavelengths, and collecting broad-band spectroscopic data on X-ray binaries, active galactic nuclei, supernova remnants, galaxy clusters, and stellar coronae.

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Last modified: Thursday, 24-Sep-2020 17:21:49 EDT