The Tethered Satellite System as a new remote sensing platform

Abstract

The Tethered Satellite System is a joint US-Italian programme for the study and design of a sub-satellite deployed from the Shuttle by means of a long tether. Two preliminary demonstration flights (the first upwards, the second downwards to 100 km) have been proposed to conduct several scientific and engineering experiments. Furthermore an improved multipurposes tethered platform is under study, to be deployed by future space stations at different low altitudes, where free-flying satellites have a short lifetime. Starting from the existing characteristics, the authors analyse the improvements necessary to achieve the performance required for remote sensing operational missions. Several authors have shown that, in station keeping, a tether control allows the longitudinal and in-plane/out-of-plane oscillations to be damped. Therefore the sub-satellite position can be accurately controlled and measured, also using active tracking systems during the short observation time interval. As far as attitude is concerned, a deeper study is needed to identify the attitude measurement and control systems of the future multipurpose platform. In order to obtain a design value representing the most stringent condition, the along-track stereoscopic coverage using linear arrays is considered. After an analysis of the attitude stability rate required by STEREOSAT and MAPSAT, and of the geometric errors involved in this kind of observation, it is shown that a value of 10⁻⁴deg/s or better will allow the multipurpose tethered platform to be used for different remote sensing missions.