Planet-Hunting Starshade Put to the Test

“Starshade” technology that could help astronomers find and characterize rocky, Earthlike alien worlds was put to the test earlier this year in the Nevada desert.

A starshade, also dubbed an external occulter, is a precisely shaped screen that flies in far-away formation with a space telescope. The device blocks a star’s light to create a high-contrast shadow, so that only light from an orbiting exoplanet enters the telescope for detailed study.

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While a starshade to hunt alien planets has not been flown before, researchers studying the technique are drawing upon a track record of success in fielding large, deployable antennas in space. Some designs foresee a fully deployed starshade measuring some 110 feet (34 meters) in diameter, with a 65-foot (20 m) inner disk and 28 outstretched flowerlike petals, each over 22 feet (7 m) in length. [7 Ways to Find Alien Planets]

Subscale testing

The starshade idea has moved beyond the drawing board.

Subscale versions of starshades have undergone nighttime desert testing, most recently at central Nevada’s Smith Creek dry lake bed over five nights in late May and early June of this year. Previously, a California test locale was used. [How the Planet-Hunting Starshade Unfolds in Space (Video)]

Desert appraisals of hardware have focused on how computational optical predictions stack up against in-the-field performance of two different starshade shapes, said Steve Warwick, program manager for starshade field testing at Northrop Grumman Aerospace Systems.

The recent Nevada test took advantage of the thin air and very dark skies at high-altitude Smith Creek, Warwick said. A six-person team made use of a modified Celestron telescope and ultrabright, light-emitting diodes (LEDs) placed about 1 mile (1.6 kilometers) away. The LEDs were all finely aligned with an automated stand topped by a starshade model sitting in the middle of the test range.

Data and images were gathered at the telescope stand.

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“As you can imagine, we take a lot of data while we’re sitting out there in tents at night,” Warwick told Space.com. “There is a lot of post-processing that we have to do … and that’s underway at the moment.”

A lot will be asked of a starshade on a planet-hunting space mission.

“What we’re trying to do here is look at a lighthouse from a mile away and spot a firefly that’s just a half inch away from that lighthouse,” he said. “We’re trying to block the light from the lighthouse.”

In the simplest terms, a starshade is a specially shaped finger placed in front of a bright source to dim the light, said Ron Polidan, manager of science systems at Northrop Grumman Aerospace Systems.

“So in essence you can consider it a traveling dark spot,” Polidan said.

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