ABOUT ELECTRODYNAMIC TETHER, ITS STABILIZATION, ITS ADVANTAGES. In an “electrodynamic tether drag” system, such as the Terminator Tether, the tether can be used to reduce the orbit of the spacecraft to which it is attached. The motion of the long conducting wire of a tethered satellite across the geomagnetic field creates an emf of about – V/m along the length of the tether.

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An EDT can use these principles in two ways: An EDT can generate electric current flow towards the planet; this can provide enough electricity to run experiments on board a satellite; this also causes the tether to experience a force from the planet’s magnetic field that is opposite the tether’s direction of motion.

By adding a battery or solar panel to the EDT circuit, the induced current is overcome, reversing the current direction; the force experienced by the tether is now in the same direction as the EDT’s motion. In other words, this produces thrust, raising its orbital attitude.

A tether moving from west to east through the Earth’s northward-pointing magnetic field will experience a current flow down the tether. The anode end of the tether collects electrons from flectrodynamic ionosphere and ejects them from negatively charged cathode; the ionosphere is electrically conductive and completes the circuit.

Electrodynamic tether

Steady current for onboard power results. A 20 kilometer tether in low earth orbit LEO could produce up to 40 kilowatts of power; this is enough to run manned research facilities. As discussed, this method of creating electrical power has a serious side-effect, namely, that the spacecraft or satellite will experience drag. That is, it will slow down and seek a lower orbit, eventually crashing on the planet.


However, there is a way to turn this “bug” into a feature. One problem that is getting worse around Earth is that of discarded “space junk” see illustration below. This property of EDTs could be used to bring down this junk earlier and in a controlled fashion. At the end of a satellite’s life or a rocket stage, or anything elseit is given a signal to release a long wire antenna.

A current will flow in the wire, and the satellite will begin to slow down, quickly heading for burn-up in the atmosphere. The second use of EDT is really amazing. The International Space Station will require over seventy tons of propellant over the next ten years to keep its orbit from decaying. A properly deployed EDT, combined with another power source, could actually push itself forward on the Earth’s magnetic field, speeding the IST up without the use of any propellant.

This will have profound implications on missions to other planets, since satellite missions will no longer need to carry expendable propellant to continue their missions. An EDT can be used to alternately boost to a new location, and then reverse current and use the resulting drag force to decellerate and fine-tune its orbit.

This greatly extends the useful life of these space probes. So why aren’t EDTs in widespread use?

The biggest eelctrodynamic are electromechanical; EDTs experience high voltages in space. Also, EDTs are prone to vibrations that produce significant mechanical forces. Also, development has tefher slow; a program planned for launch inProSEDs, was repeatedly postponed and ultimately canceled. Science fiction author David Brin has made a good story from available; you might want to go read Tank Farm Dynamo.

This story is a poignant tale of what might have been in the last century of American space travel.

The story takes maybe fifteen minutes to read – it’s well worth it! Long space tethers don’t need to be conductive to have unusual effects – see this article on generating artificial gravity with tethers. A lot of the background information for this article was found in Electrodynamic Tethers in Space from the August issue of Scientific American; unfortunately, it’s not free. Thanks to yet another alert reader for the scoop on this story. This Science Fiction in the News story used with permission from Technovelgy.

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Bill Christensen tethed the inventions, technology and ideas of science fiction writers at his website, Technovelgy. He is a contributor to Live Ellectrodynamic and Space. This idea could act as a Hypersonic Airplane Space Tether Orbital Launch system, or be utilized to handle other launch systems other than hypersonic airplanes. An electrodynamic tether EDT is a simple idea, but one with an amazing number of uses.

electricity – How does an ElectroDynamic Tether (EDT) clear space debris? – Physics Stack Exchange

An EDT system is made up of two masses in orbit connected by a long, flexible, electrically conductive cable; the tether is essentially a wire that moves through the magnetic field of the Earth or another planet or large body. An EDT takes advantage of two basic principles of electromagnetism: While it is not a colorful as the Rasta space tug from William Gibson ‘s Neuromancerit could provide a technology that takes low-flying satellites to a new level.

Bill Christensen, Bill Christensen catalogues the inventions, technology and ideas of science fiction writers at his website, Technovelgy.