Quasi-static electric field measurements made with the plasma diagnostics package in free flight during Spacelab-2

As part of the Spacelab-2 mission on the Plasma Diagnostics Package (PDP) was released from the shuttle as a free flying satellite. The shuttle performed maneuvers around the PDP in order that the ionospheric plasma around the shuttle might be studied. One objective of the PDP was to measure quasi-static electric field sin the vicinity of the shuttle. During most of the free flight, the measured electric field was comparable to the induced electric field due to the orbital motion of the spacecraft. At certain times, when the shuttle thrusters were operating, decreases in the motional electric field by 10% to 20% were observed. During times when an electron beam was ejected from the shuttle, large signals were also recorded. These large signals were probably not due to ambient electric fields, but can be attributed to three causes: differences in fluxes of streaming electrons to the two probes due to shadowing by the PDP chassis, depressions in the plasma density caused by the PDP wake, and spatial gradients in the fluxes of energetic electrons reaching the probes. At 80 or more meters downstream from the beam, the energetic electrons had a preferential direction of motion opposite to the beam injection direction