HUGE buildings could be conjured up in space using nothing more than focused radio waves to push individual components into place. Radio-controlled construction would get around one of the obstacles to colonising space 鈥� the need to ferry heavy construction equipment into orbit and support the people who will operate it.
Narayanan Komerath, an aeronautical engineer from the Georgia Institute of Technology, got the idea from a technique called 鈥渁coustic shaping鈥�, in which sound waves are used to build solid objects in weightless environments (New 杏吧原创, 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 鈥渘odes鈥�, which they can鈥檛 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.
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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鈥檚 wavelength. Light can move nanoparticles for example, while microwaves 鈥� and audible sound waves 鈥� 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鈥檚 Institute of Advanced Concepts 鈥� 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鈥檚 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鈥檛 yet calculated how much power you would need to run the satellite dishes, although he says 鈥渋t will probably be huge鈥�. But he points out that arrays of solar cells in space could easily be kilometres across. And because such a project probably won鈥檛 be feasible for several decades, solar cells may be much more efficient than they are now.
The scale doesn鈥檛 daunt NIAC director Robert Cassanova. 鈥淲e see the idea as a way to build very large structures in space economically and with a minimum of manual labour,鈥� he says. 鈥淚f you鈥檙e able to move materials using waves, you could eliminate the need for large numbers of astronauts and the infrastructure to support them.鈥�
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.
