Narayanan Komerath, an aeronautical engineer from the Georgia Institute of Technology, got the idea from a technique called "acoustic shaping", in which sound waves are used to build solid objects in weightless environments (New Scientist, 1 September 2001, p 32). Speakers in a closed chamber transmit sound waves that can push, say, plastic beads around. The beads come to rest in acoustic dead spots called "nodes", which they can't easily escape from because the air pressure at all surrounding points is higher.
The arrangement of the speakers determines the position of the nodes, precisely controlling the shape and size of the resulting object. Once the nodes are filled, the object can be solidified with a hardener such as epoxy resin.
Of course, using sound waves would be impossible in the airless vacuum of space. But Komerath reasoned that electromagnetic waves should also be able to create a force field that can push objects around. He and his students have calculated that it would be feasible to use waves to move objects with diameters smaller than five per cent of the radiation's wavelength. Light can move nanoparticles for example, while microwaves - and audible sound waves - can shift objects millimetres or centimetres across.
But the heavy lifting would be left to radio waves. Given a few months to do the job, Komerath says they should be able to assemble rocks, brick-sized or bigger, into any given shape. Later this month he will discuss his idea at a conference in Atlanta for NASA's Institute of Advanced Concepts- a think tank of the 88-member Universities Space Research Association.
As a demonstration, he suggests sending a squad of solar-powered radio transmitters to the Earth's asteroid belt and blasting one of the rocks into small pieces. Radio waves from the transmitters would then shape the resulting debris into any desired structure. Individual parts could be fused together using focused sunlight or a more conventional adhesive, forming a space where astronauts could live and work shielded from radiation.
Komerath hasn't yet calculated how much power you would need to run the satellite dishes, although he says "it will probably be huge". But he points out that arrays of solar cells in space could easily be kilometres across. And because such a project probably won't be feasible for several decades, solar cells may be much more efficient than they are now.
The scale doesn't daunt NIAC director Robert Cassanova. "We see the idea as a way to build very large structures in space economically and with a minimum of manual labour," he says. "If you're able to move materials using waves, you could eliminate the need for large numbers of astronauts and the infrastructure to support them."
If Komerath gets more funding from NIAC, he expects to have a scaled-down version using microwaves ready to fly on the space shuttle by 2009.
Author: Bennett Daviss
New Scientist issue: 12 October 2002
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