Filter Wheel Synchronisation with Scan Mirror Stepping in Sounder Payload of Insat 3D

摘要

Sounder is a payload used for sounding and atmospheric modeling onboard the INSAT 3D meteorological satellite. It is a 19 channel discrete radiometer used to generate specific data parameters for atmospheric vertical temperature and pressure profiles, surface and cloud top temperature from geostationary orbits. The Scan Mirror Assembly with an elliptical mirror with associated drive electronics and the filter wheel are the vital parts of the Sounder payload. While the scan mirror scans the earth and its environs, the filter wheel places the interference filters in the optical path sequentially for the sounding operation. The Scan Mechanism Assembly (SMA) consists of the Scan Mirror Mechanism (SMM), Filter Wheel Mechanism (FWM) and Scan Mirror electronics (SME). SME drives the elliptical Silicon carbide mirror on a two axes gimbaled Mechanism. The scanning is effected by independent East- West movement in every 100ms, followed by North-South stepping of the SMM. The filter wheel driver rotates a mechanism housing eighteen filters at 600rpm in synchronism with the elliptical mirror for sounding.A novel method has been developed for synchronization of the Filter Wheel rotation with the Scan mechanism stepping. The controller ensures that the speed of the Filter wheel is maintained precisely at 600 rpm and instantameous positions variation is within ±100 μS in terms of time. In this paper, details of the method developed and used for the synchronization has been presented.The system is qualified and operational onboard INSAT-3D. The filter wheel synchronization to mirror is achieved well below 50 μS in time in all environments on ground and onboard.