Could Future Telescopes Do Without the Mirror?

Tomorrow’s Hubble might be the size of a dinner plate.

An artist’s conception of SPIDER, the lightweight array proposed by Lockheed Martin to replace the huge—and hugely expensive—space telescopes. SPIDER dumps the cumbersome mirror.

Today’s telescopes can see better and farther than ever, but they have become expensive: NASA’s Kepler spacecraft, which discovered planets orbiting far-away stars, and the Large Synoptic Survey Telescope nearing completion in Chile, for example, each cost about half a billion dollars.

Researchers at Lockheed Martin have a radical proposal: Build the observatory without the telescope—sort of. The idea, called Segmented Planar Imaging Detector for Electro-optical Reconnaissance, or SPIDER, begins with large arrays of silicon chips called photonic integrated circuits (PICs). Each chip in SPIDER takes a wide-open image, like a mirror with no focusing point. Then a computer combines the images, gradually eliminating the blurring, in a method called interferometry. By the time thousands of PICs are combined, the image should be as sharp as one produced by a large—and expensive—telescope mirror.

“The biggest advantage of using PICs in place of traditional telescope focusing is the shrinkage in size,” says Qing Gu, a photonics researcher at the University of Texas at Dallas. The telescope’s length, once determining its magnifying power, can now be shortened to the size of a flat detector with PICs sitting side by side. “The 3D problem becomes a 2D problem,” says Gu.

The first SPIDER, with 30 PICs, isn’t yet a substitute for professional telescopes, and it will be some years before one is; Lockheed is calling it “generation-after-next” technology. Gu (who is not involved with SPIDER) notes that PICs currently respond, for example, only to a small range of light wavelengths (a single color), while classical telescopes can process a much wider range.

By eliminating mirrors and the structure needed to support them, SPIDER could reduce a telescope’s mass by up to 90 percent—a major benefit if it’s being launched into space. With SPIDER, future space telescopes could see farther, while costing much less.

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This story is a selection from the February/March issue of Air & Space magazine

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