Polarization of spacecraft generated plasma clouds

Observations made on the space shuttle during the STS‐3 flight indicate that generation of dense plasma from sources aboard the orbiter was accompanied by substantial reduction of electric potential measured by probes fixed on the orbiter. In a separate experiment increased plasma densities were observed to follow the release of neutral gas. In this letter, it is argued that both observations are consistent with the shielding of the electric field, , associated with the motion of the orbiter across the earth's field from the interior of the spacecraft generated plasma. As a consequence the downstream drift of the part of the plasma cloud near the vehicle may be much less than the drift speed experienced by a single charged particle released from rest in the vehicle's frame. Since the ion thermal velocities with which plasma expands along field lines are typically much less than , this consequence can have a substantial impact on the determination of spacecraft generated plasma densities near the orbiter.