Drag and propulsion of large satellites in the ionosphere: An Alfvén propulsion engine in space

There is a motionally induced charge separation in a conductor moving across magnetic field lines. This charge may be conducted away, resulting in a dc current flow through the conductor if it moves through a plasma. The generation of Alfvén waves is a mechanism particularly effective for circulating the charge for very large conductors moving in or above the earth's ionosphere. This mechanism is studied in this paper and when applied to the analysis of the orbit of the Echo satellite is found to give rise to a significant damping of the motion as mechanical energy is converted to that of Alfvén radiation. The calculated drag is comparable to that observed for the orbit of Echo 1 and attributed in earlier studies entirely to the mechanical drag of considerable nonionized atmospheric density. Perturbations in electron density associated with this current flow may in appropriate circumstances be detectable even thousands of kilometers away from such a high altitude satellite. The drag can be changed to a propulsion mechanism when a source of electrical power is available on the satellite. Up to fifty per cent of the expended power is available for pushing a space vehicle across an ambient magnetic field.