TETHERED-SATELLITE SYSTEM (TSS) - PRELIMINARY-RESULTS ON THE ACTIVE EXPERIMENT CORE EQUIPMENT

The first Tethered-Satellite System (TSS-1) Electrodynamic mission has been launched aboard the Space Shuttle STS-46 on July 31, 1992, as a joint mission between the United States and Italy. A 500 kg spherical Satellite (1.6 m diameter) attached to the Orbiter by a thin (0.24 cm) , conducting, insulated wire (Tether), has been reeled upwards from th e Orbiter payload bay to a distance of 257 m when the Shuttle was at a projected altitude of 300 km. ASI, the Italian Space Agency, had the responsibility for developing the reusable Satellite, while NASA had t he responsibility for developing the Deployer system and the Tether, i ntegrating the payload and providing transportation into space. One of the main scientific goals of this first mission was to demonstrate th e possibility of energy conversion from mechanical to electrical by us ing a long Tether orbiting through the Earth's magnetic field. ASI des igned and developed an active experiment, referred to as Core Equipmen t, in order to carry out this demonstration. The experiment used two E lectron Generator Assemblies (EGAs), located on the Orbiter, to re-emi t into the ionosphere as an electron beam the electrons collected on t he Satellite from the ionosphere. Each EGA had the capability to emit an electron beam with a programmed intensity from 10 mA up to 750 mA w ith a resolution of 3 mA. The perveance of each EGA was 7.2 microperv, and the beam energy, up to 3 kV, was provided as part of the e.m.f. i nduced across the TSS due to its motion through the Earth's magnetic f ield. Other instruments provided current, voltage, and ambient-pressur e measurements, and allowed, via a series of switches, different elect rical configurations of the TSS. Moreover, the Core Equipment provided a dynamic package, to study the TSS dynamics, as a first goal, and to verify the possibility of using the TSS Satellite as a platform for f uture experiments in the microgravity field. The expected voltage acro ss the TSS was estimated to be 5 kV for a full Tether deployment of 20 km. During the mission, and due to unforeseenable reasons, the Tether deployment achieved was only of 257 m. Despite this limitation,there is evidence that the experiment was working nominally in the very low- voltage range across the TSS. This result strongly increases the confi dence in the possibility of high-voltage operation of the electrodynam ic TSS, as the Tether deployment will achieve the 20 km, as expected i n the future reflight. The paper describes the experiment, and reports some preliminary results achieved during the first mission.