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

TLDR

When a conductor moves across magnetic field lines, it induces charge separation that can drive a dc current through a plasma, and for large conductors in the ionosphere this process efficiently generates Alfvén waves to circulate the charge. The study examines how Alfvén-wave generation can damp the orbit of large satellites, and shows that with onboard power it can be harnessed as a propulsion mechanism. The calculated Alfvén drag matches the observed decay of Echo 1’s orbit, and the associated electron‑density perturbations could be remotely sensed, while up to 50 % of the satellite’s power can be converted into thrust across the magnetic field.

Abstract

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.