3-D TIME-DEPENDENT SIMULATIONS OF THE TETHERED SATELLITE-IONOSPHERE INTERACTION

A three-dimensional time-dependent fluid model was used to study the i nteraction of the TSS-IR satellite with the ionosphere. The model was configured to take account of the correct satellite size (1.6m) and ve locity (8 km/s), a realistic O+/electron mass ratio (29,150), the geom agnetic field, and the length of time the satellite stays on specific field lines. The simulation boundary was also moved far from the satel lite (similar to 20m) in an effort to minimize boundary condition effe cts. The emphasis was on positive satellite potentials just above (10 v) and below (4 v) the O+ ram energy of 5 eV. The simulations indicate d the following: (1) A very long, field-aligned, cylindrical potential structure forms, which has a radius slightly larger than the satellit e radius; (2) A sheath forms around the satellite in a toroidal region in the equatorial plane, but does not form in the cylindrical volume where the B-field intersects the satellite. The sheath E-field is mapp ed along B and exists in a thin cylindrical shell with radii that exte nd from the satellite surface (R-s) to about 1.3 R-s; (3) The sheath i s asymmetric due to the satellite motion across B, but this makes a ne gligible contribution to the collected current because of the large sa tellite size; (4) For a 10-volt satellite, the sheath reflects O+ ions in the ram direction, which results in a slight density buildup in fr ont of the satellite; and (5) The bulk of the current flows along B, b ut Hall and E-field components also exist. Their magnitudes vary marke dly with position, but representative values can be given at locations where the currents are the largest. In terms of the thermal current, the parallel to B component is 4.2 along the polar axis one R-s away f rom the satellite. Close to the satellite, and in the equatorial plane and ram direction, the E x B component is 8.8 and the component paral lel to E is 2.0. The collected current is much larger than that predic ted by the simple Parker-Murphy theory.