3‐D time‐dependent simulations of the tethered satellite‐ionosphere interaction

Abstract

A three‐dimensional time‐dependent fluid model was used to study the interaction of the TSS‐1R satellite with the ionosphere. The model was configured to take account of the correct satellite size (1.6m) and velocity (8 km/s), a realistic O+/electron mass ratio (29,150), the geomagnetic field, and the length of time the satellite stays on specific field lines. The simulation boundary was also moved far from the satellite (∼20m) in an effort to minimize boundary condition effects. The emphasis was on positive satellite potentials just above (10 v) and below (4 v) the O+ ram energy of 5 eV. The simulations indicated the following: (1) A very long, field‐aligned, cylindrical potential structure forms, which has a radius slightly larger than the satellite 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 mapped along B and exists in a thin cylindrical shell with radii that extend from the satellite surface (Rs) to about 1.3 Rs; (3) The sheath is asymmetric due to the satellite motion across B, but this makes a negligible contribution to the collected current because of the large satellite size; (4) For a 10‐volt satellite, the sheath reflects O+ ions in the ram direction, which results in a slight density buildup in front of the satellite; and (5) The bulk of the current flows along B, but Hall and E‐field components also exist. Their magnitudes vary markedly 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 Rs away from the satellite. Close to the satellite, and in the equatorial plane and ram direction, the E × B component is 8.8 and the component parallel to E is 2.0. The collected current is much larger than that predicted by the simple Parker‐Murphy theory.