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An X-ray astronomy experiment for the study of spectral and temporal characteristics of cosmic X-ray sources was developed jointly by TIFR and ISRO Satellite Center (ISAC). The payload consists of three identical pointed proportional counters (PPC) and one X-ray Sky Monitor (XSM). Each of the detectors are controlled by independent microprocessor based processing electronics. A common electronics sub-system acts as an interface with the satellite bus. An oven controlled oscillator (accuracy one part in 109) provides high timing accuracy. The Indian satellite IRS-P3, carrying the X-ray astronomy instruments was launched on 1996, March 21 with Indian Polar Satellite Launch Vehicle PSLV-D3 from Shriharikota Range, India..

 (P.C. Agrawal, A.R. Rao, B. Paul, M. R. Shah, J.P.Malkar, K. Mukherjee, S. Sardesai, D.K. Dedhia, P. Shah, M.N. Vahia, J.S. Yadav, S.V. Damle, V.M. Gujar, S.S. Mohite, D.P. Pawar, A.N. Patil, A.P.K. Kutty) 

The Indian Cosmic Ray Experiment Anuradha on board Space Shuttle Spacelab-3 was specially designed to measure the ionization states of low energy cosmic rays in near earth space. The experiment used high resolution large area CR-39 (DOP) track detectors and a mechanical device to provide time resolution. This instrument was flown in space in NASA's Space Shuttle Spacelab-3 during 1985 April 29 to May 06 at an altitude of 370 Kms and inclination of 57 . This experiment provided first unambiguous direct measurements of ionization states of individual Nitrogen, Oxygen and Neon ions of ACR. For further details see

http://meghnad.iucaa.ernet.in/~astrosat/sxt_specs.html

The X-ray Sky Monitor(XSM) on The Satellite IRS-P3 ----------------------------------------------------------------

 The XSM is a planar position sensitive proportional counter with a pin-hole of 1 cm2 positioned 16 cm above the detection plane. The FOV is 90o X 90o. The detection plane consists of 32 proportional counter cells with a resistive wire (NiCr?) as the anode. Position resolution along the wires is achieved by charge division and perpendicular to the wires it is achieved by cell placing (1 cm). It is estimated that for bright sources (100 mCrabs) a source localization accuracy of 0.1 degree can be achieved. The energy range of the detector is 3 to 6 keV. The front end electronics of XSM is mounted at the back side of the detector. It includes command controllable HV DC/DC convertor, 17 charge sensitive amplifiers and an intricate logic circuit. The layout of these electronics cards are carefully designed to accommodate all the circuit in the minimum available space. The logic circuit evaluates the X-ray events and digitizes the outputs from the two ends of the anodes such that the charge division can be done digitally. The onboard processor controls the detector, accepts the digitized data for each X-ray event and calculates position and arranges the data in the available 512 kbytes memory. Coarse time resolution (1 minute) count rates; two second count rates for each anodes; pixel matrices etc. constitute the onboard data.
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