Current Collection by a Large Langmuir Probe in a Meso‐Thermal (ram) Plasma

Langmuir Probes are often used to determine plasma density and temperature. The relation between the current collected by a large spherical probe on a low-earth-orbit spacecraft and the environment parameters is different from the relation for such a probe in a non-drifting thermal plasma. Ignoring the effect of ram ions on space charge limited sheath formation can lead to erroneous values for the environment parameters. Motivated by a desire to understand the SAMPIE probe traces, we derive an expression to determine the ionosphere plasma parameters from measurements made using large Langmuir probes in low-earth-orbit.