'Starshade' Helps Identify Celestial Objects

Ground-based tests have shown promise for the use of a flower petal-shaped "starshade" in space telescope missions for finding exoplanets.

Developed at Northrop Grumman Corp., the 10-cm occulter device enabled imaging of celestial objects during March engineering tests at McMath-Pierce Solar Telescope on Kitt Peak in Arizona. This was the first time a starshade was tested against actual astronomical objects.

Future versions of the starshade would fly thousands of kilometers in front of a space telescope to block out the light of nearby stars, enabling astronomers to directly see planets surrounding those stars. The technology is specifically intended to detect Earth-like planets.

A starshade is shown positioned in front of the heliostat mirror of the McMath-Pierce Solar Telescope in Arizona to test its performance against celestial objects. The Orion constellation is reflected in the mirror. Courtesy of Northrop Grumman.

During the ground-based tests, the team experimented with three starshade designs: a circular shape and two petal-shaped designs. The petal-shaped designs demonstrated the best performance, allowing the team to clearly view objects surrounding Jupiter, Saturn, Venus, and the stars Sirius and Vega.

"The physics of the circular shape have been known for years," said Steve Warwick, a systems engineer and test lead with Northrop Grumman Aerospace Systems. "We were amazed at just how effectively the petal-shaped starshade design canceled the light coming from very bright planets and bright stars. These tests added considerably to our engineering knowledge and opened the possibility that the McMath starshade demonstration can collect scientifically important data that might not be attainable any other way."

The McMath-Pierce Solar Telescope is the largest solar telescope in the world, standing nearly 100 feet tall and featuring a shaft that slants two hundred feet to the ground. Courtesy of Northrop Grumman.

The 2.1-m heliostat mirror at McMath-Pierce is conducive for starshade research because it provides distance between the starshade and the imaging telescope while tracking stars and planets to the accuracies required for long exposure times.

McMath-Pierce is operated by the Association of Universities for Research in Astronomy Inc. under a cooperative agreement with the National Science Foundation.

Northrop Grumman has been working on the starshade, associated engineering and enabling technologies since 2004. The company performed tests in the Nevada desert in 2014 and 2015 using an LED as the star source, but the tests at McMath-Pierce represent the first substantial times the starshade was tested against celestial bodies.