|
The era of space-age tethered operations moves toward reality with the launch of TSS-1. The primary objective of this mission is to demonstrate the technology of long tethered systems in space and to demonstrate, through scientific investigations, that such systems are useful for research.
Engineering Goals
Manipulating a satellite on a tether from the orbiter is a unique engineering challenge. Because gravity, centrifugal force, and atmospheric drag vary with altitude, each of the two bodies in a tethered system, one orbiting above the other, is subject to different influences. Consequently, the primary engineering goal of TSS-1 is to demonstrate that a satellite can be deployed, stabilized, and retrieved on a long tether in space and that an electrically conducting system can be operated successfully. Tether dynamics and control are not intuitive; while reeling out a satellite on a tether is somewhat analogous to flying a kite, the analogy breaks down when the environment in which the system operate are compared. Unlike a kite in the atmosphere, the tethered satellite is in an electrically charged environment and is controlled by gravity gradient rather than aerodynamic forces. TSS-1 will improve our understanding of tether dynamics and allow scientists and engineers to develop more sophisticated tether control models for future tethered missions.
Science Goals
Speeding through the magnetized ionospheric plasma at almost 8 km per second, the 20-km long conducting tether should create a variety of very interesting plasma electrodynamic phenomena. These are expected to provide a variety of unique experimental capabilities, including the ability to collect an electrical charge and drive a large current system within the ionosphere, to generate high voltages [on the order of 5 kilovolts (kV)] across the tether at full deployment, to control the satellite potential and the satellite's potential sheath, and to generate low-frequency electrostatic and electromagnetic waves. It is believed that these capabilities can be used to conduct controlled experimental studies of phenomena and processes that occur naturally in plasmas throughout the solar system, including Earth's magnetosphere.
A necessary first step toward these studies - and the primary science goal of TSS-1 - is to characterize the electrodynamic behavior of the sateliite-tether-orbiter system. Of particular interest is the interaction of the system with the charged particles and electric and magnetic fields in the ionosphere, including the nature of the external current loop within the ionosphere and the processes by which current closure occurs at the satellite and the orbiter. This will be investigated by a series of experiments conducted with electron accelerators and tether current-control hardware, along with a set of interdependent diagnostic instruments provided by the TSS-1 investigators.
Back to Tether Main
This page contains excerpts from the brochure: "The First Mission of the Tethered Satellite System" developed by the Tethered Satellite System Project Office, NASA/Marshall Space Flight Center (MSFC), Huntsville, Alabama. Authors are C. Blake Powers, Charlotte Shea, and Tracy McMahan, all of the Essex Corporation.
|
