HIGH-PERFORMANCE LANDSAT/SPOT DUAL S-/XBAND TELEMETRY TRACKING AND RECEIVING SYSTEM

Abstract

A high-performance dual S/X-band telemetry tracking and receiving system has been developed to provide a low-cost earth station for receiving high-resolution data from current and future LANDSAT/Spot polar orbiting satellites. The antenna system consists of a dual S/X-band telemetry tracking feed in a Cassegrain configuration with a 10-meter parabolic reflector designed for 100 mph wind loading and 10 deg/sec accelerations. The 2 antenna system is mounted to a newly-developed elevation-over-azimuth tracking pedestal, which incorporates the latest technology in a dual brushless d.c. servo motor torque-biased drive train for each axis. This drive train provides an exceptionally wide dynamic range in trlcking velocities for very slow horizon tracking and very fast velocities for near-overhead passes. A microprocessor-based servo control system using the latest state variables feedback and adaptive control techniques is used to provide accurate tracking for both slow and fast rates. A 15-km satellite pass distance from overhead is used as a control system design criterion. For the narrow beamwidth X-band track this requires an acceleration error of less than 0.100 degree and an acceleration error constant of at least 90 sec . The requirement for a high-performance servo system with the low -2 structural resonances of a large antenna constitutes a difficult stability problem.