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Superconductors enable magnetic flux pinning for spacecraft

Posted: 04 Apr 2008 ?? ?Print Version ?Bookmark and Share

Keywords:superconductor? permanent magnet? space station module? magnetic flux pinning?

Cornell University researchers propose that superconductors paired with permanent magnets could enable spacecraft to hover unpowered above the ground in the same way Luke Skywalker's space racer hovered in the seminal Star Wars movie.

Superconductor technologies designed at Cornell aim to hold space-station modules and satellites in place without tethers or retrorockets by magnetically "pinning" them in place. Using unpowered superconductors and fixed permanent magnets, the Cornell researchers claim a new-age solution to longstanding stability and control problems in space vehicles.

Unpowered stability
Cornell hopes to prove the concept of magnetic pinning using unpowered superconductors for NASA spacecraft that must assemble themselves in orbit without the help of astronauts. Within six months, the researchers plan to have a working test bed in place to verify that unpowered superconducting architectures can stabilize and control spacecraft.

"We believe that magnetic pinning with superconductors will enable much more stable space platforms to be constructed and held together without physical connections," said Cornell professor Mason Peck. "Modules that are magnetically pinned will also have a built-in bumper that prevents them from accidentally bumping into each other, potentially preventing the kind of damage that is hard to repair in space."

Magnetic pinning works by placing two space modules!one with an unpowered, but supercooled, superconducting coil and the other with an ordinary permanent magnet!near each other. The permanent magnet induces a current in the superconductor that is persistent and exactly opposite to the field of the magnet. In essence, one essentially "grips" the other with an invisible magnetic glove.

"When you bring a permanent magnet near a superconductor, it induces a current that stays there and exactly opposes the magnet's own field!these are tiny current loops at the quantum level," said Peck. "This in effect links the two objects with equal, opposing magnetic fields that keep them hovering next to each other indefinitely without supplying any external power. Even when external forces perturb them, they will maintain both their rotational and translational position."

The cold of space is enough to make the superconductors work!although for spacecraft inside the orbit of Mars, the superconductors will have to be shaded from direct sunlight in order to maintain their grip. With proper design, however, it should be possible to pull together and latch freestanding space modules without physical tethers, by rotating solar shades to provide solar heating and cooling that activates and controls the magnetic pinning functions.

Self-assembly
Peck and his colleagues since 2005 have experimented with magnetic superconducting building blocks that self-assemble without physically touching. The initial funding for the Cornell project was under NASA's Institute for Advanced Concepts, where Peck first showed how rotational and translational degrees of freedom could be fixed with magnetic flux pinning.

"We can place them in close proximity and let the magnets do the rest, never actually having to physically touch each other and without requiring power to maintain their positions and orientations," said Peck.

To perform micro-positioning functions, Peck plans to include tiny electromagnets that can be turned on and off to exactly position two modules, after which all the electromagnets could be powered down to lock the assembly into place.

"We believe that flux pinning can be used to assemble spacecraft in a reliable, safe and permanent way, but without all the pitfalls associated with mechanical components," said Peck.

By funding Peck's work, NASA hopes to chuck traditional single-spacecraft architectures in favor of clusters of wirelessly interconnected spacecraft modules!each able to contribute a unique capability to the cluster. These interconnected modules would travel in a loose formation to create a virtual spacecraft capable of delivering more than the sum of its parts.

"The biggest advantage of our approach to building such distributed, modular spacecraft is that if you have a power failure, the spacecraft does not start falling apart!all the components would remain in their relative locations despite any loss of power," said Peck.

Peck's current test bed resembles an air hockey table that simulates weightlessness for pint-size modules. But within six months, he pledges to have a new test bed that will be capable of testing (on Earth) satellite-size modules pinned into position using superconductors and magnets. He predicts that the first in-space test will be to hold together the components of a simple communications satellite that are launched piecemeal, and then assembled with magnetic pinning.

- R. Colin Johnson
EE Times





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