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.