NEGATIVE SHUTTLE CHARGING DURING TSS 1R

We studied 21 intervals during the TSS 1R deployment with a 15 Ohm or 25 k Ohm resistor connecting the tether to shuttle ground. Ion spectra l peaks detected by the Shuttle Potential and Return Electron Experime nt indicate that the shuttle consistently charged negatively with resp ect to the local plasma. With the 15 Ohm shunt in the circuit, shuttle potential, Phi s, decreased from -17 to -245 V as tether length, L, i ncreased to 2.6 km. Current in the circuit depended strongly on ionosp heric density. With the 25 k Ohm resistor in place, Phi s approximate to -300 V in the low density, nightside ionosphere with L = 5.1 km. Ne ar local noon Phi s approximate to -80 V with L = 17.2 km. The shuttle charged to similar to -600 V during two dawn terminator crossings, on e with and one without thruster firings. As on TSS 1, firings of two a ft vernier thrusters significantly increased \Phi s\. In the case with out thruster firings, simultaneous variations of Phi s, tether current , and the inferred satellite potential are consistent with strong azim uthal and vertical ionospheric density gradients. These are the first known direct measurements of strong negative shuttle charging.