A HGI2 X-RAY INSTRUMENT FOR THE SOVIET MARS 94 MISSION

Considerable progress has been achieved in recent years in the manufacturing and performance of ambient temperature HgI2 X-ray detectors and their associated low noise electronics, so they are now being considered for space applications. The Soviet Mars '94 is the first mission to investigate the surface and the atmosphere of the planet Mars with a complex series of instruments. An Alpha backscattering instrument with alpha, proton and X-ray modes has been proposed and selected for that mission. The X-ray mode of the instrument uses ambient temperature HgI2 X-ray detectors and low noise electronics with expected resolution of 200-250 eV FWHM at 5.9 keV. Such an instrument will obtain the detailed and complete chemical composition (except hydrogen) of the Martian surface at several sites. In the paper, the design of the X-ray flight instrument, the detectors and the low noise electronics, as well as mission operation and the expected results, will be described in detail. Laboratory performance of a HgI2 based detector system will be shown.