Design of a single-axis platform for balloon-borne remote sensing

Abstract

We describe the design of two telescope pointing systems for remote optical sensing of the stratosphere from a balloon-borne gondola. The telescope pointing accuracy is ±0.02° in elevation, from a gondola which has static and dynamic tilts up to ±3°. Each system consists of a telescope, an elevation control subsystem, and a pitch-stabilized single-axis reference platform. The Mark I unit has performed successfully on each of its two balloon flights, for a total of over 16 h in the stratosphere; the Mark II unit is currently under construction. The single-axis platform is referenced to a rate-integrating gyroscope and an inclinometer for high- and low-frequency pitch-angle variations, respectively. The Mark I platform is supported by ball bearings, driven by a brush-contact torque motor, and is subject to a small, permanent pitch angle error which depends directly on the gyro drift rate. The Mark II platform uses flex-pivot supports, a brushless motor, and for even a relatively large gyro drift rate, is designed to asymptotically approach zero angular offset error.