Current collection at the shuttle orbiter during the tethered satellite system tether break

摘要

We present measurements of currents, orbiter potentials, and plasma spectra during high-voltage arcing coincident with the tether break event on the Tethered Satellite System reflight. In addition to the unexpectedly high tether currents observed, plasma spectra indicate the presence of ion and electron populations with broad energy ranges. These data were used in combination with satellite and orbiter current collection models to investigate the circuit behavior of the system's components. We find that arcing at the lower end of the tether supported the current flow in the tether during each phase of the break event, but with different mechanisms dominant depending on the location of the break point. With the break point inside deployer control structures, current arced to the orbiter ground, charging it to high negative potentials and allowing secondary ionization of neutral molecules near orbiter conducting surfaces. The most likely source of these neutrals is air trapped inside the tether at 1 atm of pressure that escaped through the hole in the tether insulation. When the break point was exposed to the exterior environment the tether current arced directly to the plasma. As long as the break point remained near the orbiter, the collection of electrons by conducting surfaces caused it to float at a low level of negative charging. The source of the energetic electrons detected in the payload bay remains uncertain. However, they can only have come from a region within the sheath that was more negatively charged than the orbiter's conducting surfaces.