Electromagnetic induction

Citation

(2001), "Electromagnetic induction", Aircraft Engineering and Aerospace Technology, Vol. 73 No. 1. https://doi.org/10.1108/aeat.2001.12773aab.007

Electromagnetic induction

Electromagnetic induction

Keywords: NASA, Satellites, Propulsion

NASA scientists have come up with another application. Scientists at NASA's Marshall Flight Centre in Huntsville, Alabama, plan to apply Faraday's principle in a demonstration of the Propulsive Small Expendable Deployer System – called ProSEDS – that uses an electrodynamic tether as a means of space – vehicle propulsion. The tether is a 3.1 mile length of bare wire that will be attached to a 6.2 mile non-conductive strand. The whole string will pay out from the second stage of a Delta H rocket, launched from Cape Canaveral Air Station.

An electrodynamic tether generates a current in its wire as it moves through the magnetic field of the Earth's ionosphere. The free end of the tether, positively biased, attracts electrons from space. Current flows as these electrons move towards the spacecraft. Just as Faraday demonstrated, the result is a force perpendicular to the direction of current flow. If the tether points towards Earth's centre as the satellite orbits eastward, the current in the tether will exert a force towards the west. This force slows the satellite, dropping it to a lower orbit.

Tethers have been tested in space before; the ProSEDS experiment will demonstrate a different and more efficient scheme for collecting electrons. Previous tethers have been protected by insulation; the new tether will be stripped to bare wire for most of its length. "The working principle of electrodynamics tethers is not new, but the application to space transportation will be revolutionary", said Les Johnson, principal investigator of the ProSEDS experiment. "Tether propulsion requires no fuel, is completely re-usable and environmentally clean, and provides all these features at low cost".

This experiment will demonstrate the tether's ability to slow the stage and place it in a lower orbit. If the direction of the current flow in a tether could be reversed by using an external power source, for instance, the force induced by the tether on a spacecraft as it orbits eastward could be towards the east as well. A craft, thus speeded up, would climb to a higher orbit.