HEO Satellite Frame and Differential Charging and SCATHA Low-Level Frame Charging

Significant amounts of satellite charging data have been taken at geosynchronous (GEO) and near-GEO orbit and in low-altitude orbits. There are only limited satellite charging measurements at intermediate altitudes or at middle to high latitudes at high altitudes. In this paper, results of spacecraft frame and differential potentials are shown that were measured over several years on a highly elliptical orbit (HEO2) satellite with an apogee of ~7.2 R
_E
geocentric and ~63deg inclination. The HEO2 frame and differential charging data were obtained using a plasma spectrometer. Measurements of HEO2 charging levels les -30 V are summarized according to their occurrence in magnetic local time and L. The data show that the HEO2 satellite frame charged to potentials les -30 V, and that the occurrence of satellite frame charging at these high latitudes mimics the charging local time patterns observed by GEO satellites. In addition, the data show that such charging extends from at least a minimum L of les 4 R
_E
to L > 10 R
_E
. It was found that the differential charging potential usually exceeded the frame potential and could be estimated by V
_D
~ 74 + 1.384 V
_F
. Separately, we show the results of a one-year study of the Spacecraft Charging AT High Altitude (SCATHA) satellite frame potential in the near-GEO region. SCATHA's frame potential was positive les 15% of the time and was ges - 1 V ~ 95% of the time. Large negative frame potentials (< - 1 V) occurred ~ 5% of the time. The data also showed that the large negative frame potentials preferentially occurred on the nightside, as expected, and that they occurred less that 1% of the time on the dayside. These statistics may be used as a reference for estimating the relative attraction of ionized outgassed contaminants for a satellite.