Astronomical Institute, 251 65 ONDREJOV, Czech Republic

The scientific and operational aims of the Hard X-Ray Spectrometer (HXRS) are discussed. The principal operating characteristics of the instrument such as the temporal resolution, energy band selection, spectral sensitivity, and the in-flight calibration procedure are described as well as the technical details of the spectrometer including: detectors, shielding (against charged particles) and electronic design. The Multispectral Thermal Imager (MTI) host satellite, its orbit and operational schedule are briefly described.