ROCKET-BORNE AND SATELLITE-BORNE X-RAY AND GAMMA-RAY EXPERIMENTS

The spectacular progress in X-ray astronomy during the last 3 decades has followed the successful refinements and adoption of measuring tech niques in the X-ray range. Various observational methods employed in t he astronomical observations are similar to those used in a radiation physics laboratory. The main considerations which characterize the exp eriments in X-ray astronomy are: (i) the strong attenuation of the X-r ay photons in the atmosphere thereby requiring observations at higher altitudes above 40 km and (ii) the photon limited regime, because the photon flux from even the strongest X-ray source is so low that indivi dual photon counting is unavoidable. This coupled with the fact that a bsorption cross-sections at higher X-ray energies are quite low, makes the choice of X-ray detectors for astronomical use rather limited. Th is, in turn, has limited the variety of experiments being conducted in the X-ray and gamma-ray regions. Presently, apart from the state-of-a rt detectors, many new concepts specifically applicable to X-ray bands age being explored. This paper traces the history of the rocket-and s atellite-borne instruments and presents a brief summary of the current practices and future projections.