Satellite Laser Ranging Precise Time Transfer Techniques: Some Comments on the Possible Indian Contribution

Abstract

Following the proposal by Bureau International de L' Heure (BIH), Paris the European Space Agency (ESA) has implemented an experimental space mission on-board SIRIO-2 geosynchronous satellite, a payload package, known as LASSO (Laser Synchronization from Stationary Orbit). The LASSO consists of body-mounted array of corner cube retro-reflectors, laser detectors, event timer, precise time standard, TTL-type memory unit and the communication link between satellite and the ground control. The LASSO/SIRIO-2 experiment is designed to employ laser technique for Intercontinental comparisons of clocks at the sub-nanosecond level and for disseminating reference time (UTC) to the user community on a global basis. The satellite is proposed to be launched by ESA in early 1982. Initially, it is planned to position the satellite at a longitude around 25°W, subsequently the satellite will be moved to 20:E. The latter position of SIRIO-2 (20°Ei is the one which will be used in Indian experiments.

As the principle, method, instrumentation and corrections needed for accurate epoch determination are dealt with in another paper in this volume, these have been only briefly touched upon as relevant to Indian experiments. The effects of laser energy, pulse width, beam divergence and receiver characteristics (both at the satellite and at the ground station) on the experiment are analysed in detail. A scientific collaboration between National Physical Laboratory (NPL) and Indian Space Research Organization (ISRO) and European Space Agency (ESA) for conducting LASSO/SIRIO-2 experiment is outlined.