Date:  Wednesday, January 10, 1996
Time:  4:15 PM ­ Refreshments at 4:00
Location:  ERL 126


Induced Ionospheric Double Probe Tether Potential Measurements and
Models for TSS-1 Electrodynamics

Scott Williams
STARLab, Deptt. of Electrical Engineering,
Stanford University

Abstract

The study of electrodynamic behavior for a long, insulated-wire tether attached
to charge collecting surfaces at each tether end was a primary first mission
goal for the Tethered Satellite System (TSS-1).  Fundamental to this
characterization was the ability to measure and understand induced potentials
across the tether operating essentially as an extremely long electric double
probe. This induced tether potential and its associated measurement is rooted
in the theory of ionospheric electric double probes and is due to several
factors, including the electromotive force from orbital motion in the
magnetized ionosphere, naturally occurring ionospheric vertical electric
fields, and other natural or man-made electromagnetic wave sources. 
 
An overview of the Shuttle Electrodynamic Tether System (SETS) experiment and
measurements from the TSS-1 mission will be presented.  While tethered
satellite deployment for the first mission was limited to 268 m and tether
motional EMF potentials limited to less than 60 V, it was still possible to
make highly accurate potential measurements relative to Orbiter electrical
ground using the SETS Tether Current and Voltage Monitor (TCVM). Typical
measurements of the TSS-1 induced potentials and sources of error will be
described. The unique ability of very long tethered double probes to minimize
some error terms and the implications of the results for the upcoming TSS-1R
mission, scheduled for next month, at which a full tether deployment is
anticipated, will be discussed.