Abstract. The Soft X-ray focusing Telescope (SXT), India's first X-ray telescope based on the principle of grazing incidence, was launched aboard the AstroSat and made operational on October 26, 2015. X-rays in the energy band of 0.3-8.0 keV are focussed on to a cooled charge coupled device thus providing medium resolution X-ray spectroscopy of cosmic X-ray sources of various types. It is the most sensitive X-ray instrument aboard the AstroSat. In its first year of operation, SXT has been used to observe objects ranging from active stars, compact binaries, supernova remnants, active galactic nuclei and clusters of galaxies in order to study its performance and quantify its characteriztics. Here, we present an overview of its design, mechanical hardware, electronics, data modes, observational constraints, pipeline processing and its in-orbit performance based on preliminary results from its characterization during the performance verification phase.

Charged Particle Monitor (CPM) on-board the AstroSat satellite is an instrument designed to detect the flux of charged particles at the satellite location. A Cesium Iodide Thallium (CsI(Tl)) crystal is used with a Kapton window to detect protons with energies greater than 1 MeV. The ground calibration of CPM was done using gamma-rays from radioactive sources and protons from particle accelerators. Based on the ground calibration results, energy deposition above 1 MeV are accepted and particle counts are recorded. It is found that CPM counts are steady and the signal for the onset and exit of South Atlantic Anomaly (SAA) region are generated in a very reliable and stable manner.

The use of a tungstic oxide semiconductor as a sensor for ozone at concentration levels relevant to atmospheric monitoring applications is an important advance in attempts to produce cheap, lightweight and reliable instruments. Problems of stability are a possible obstacle to this application. A model that describes the response of these sensors to ozone is proposed here and using it an explanation for the drift of resistance with time at constant concentrations of ozone is given. Consideration of this drift model enables a measurement routine to be employed that compensates for the drift observed experimentally, thus producing a reliable calibration of the sensor.

The behaviour of gas-sensitive resistors based on WO3 towards small concentrations of ozone in air can be understood with a simple model involving the reaction of ozone with surface oxygen vacancies. This model has been validated by comparison with experimental results for the effects of varying oxygen partial pressure on the ozone response. A complete description of the behaviour of devices constructed by printing WO3 as porous layers onto an impermeable substrate requires consideration of the effects of the microstructure of such a device upon its response. A very simple series-parallel equivalent circuit model captures the effects and allows a simple interpretation of the sensor behaviour, including the quadratic limiting steady state resistance response to ozone and the effects of variation of device thickness. An important fact that allows WO3 to be used at rather high temperatures as an effective ozone sensor is that ozone does not decompose at any discernible rate on the oxide surface. Saturation of the oxide surface at ambient temperature with water vapour inhibits the ozone response when the sensor is subsequently heated. The effect can be removed by heating at sufficiently high temperature. Water vapour also gives a high-temperature sensor response, but appears to act at sites different to those that mediate the response to ozone.

A novel X‐ray diffraction (XRD) technique, which exhibits almost complete insensitivity to the morphology of and distance to the sample, is presented for the first time. This technique applies energy‐dispersive XRD (EDXRD) in a back‐reflection geometry, with 2θ≃ 180°. Although this geometry leads to low resolution of diffraction peaks and the greatest overlap with fluorescence peaks, it nevertheless yields a combination of properties that are unique in the field of X‐ray diffractometry. It is likely that diffraction patterns can be obtained with no or very minimal sample preparation. Furthermore, the intrinsic geometry of the method and the simplicity inherent to EDXRD enables a compact lightweight instrument design, suitable for field‐portable or hand‐held XRD and X‐ray fluorescence analysis. Application to geological and planetary science is emphasized in this paper. The characteristics of the technique are elucidated via theoretical considerations and ray‐trace modelling, and the simplest possible implementation is described.