WASHINGTON — Among alternatives NASA is studying should plans to build the next big astrophysics observatory from a donated spy telescope fall through is a 1.1-meter telescope that would fly in formation with a new, flower-shaped external occulter known as a Starshade to search for faraway Earth-like planets.

Known as Exo-S, the mission concept is being developed to fit into a $1 billion budget. It is one of two exoplanet telescopes backstopping NASA’s first choice for a big, new astrophysics start: a combination planet-hunter and dark energy observatory called the Wide-Field Infrared Survey Telescope (WFIRST).

In 2010, as part of a 10-year science roadmap known as a decadal survey, astronomers tagged WFIRST science objectives as the second-most critical of this decade, after the observations the James Webb Space Telescope is designed to make following its 2018 launch. However, WFIRST development has been put off due to cost overruns with the now $8.8 billion James Webb Space Telescope, spending on which is not expected to slow enough to allow a successor to begin development until 2017.

NASA’s preferred successor is WFIRST-AFTA. AFTA, or Astrophysics Focused Telescope Assets, is the agency’s name for a pair of 2.4-meter-diameter telescopes donated by the National Reconnaissance Office in 2012. Including an exoplanet-hunting instrument called a coronagraph that NASA may add to the mission, WFIRST-AFTA would cost about $2.4 billion to build, according to a March 18 report from an ad hoc committee of the National Research Council’s Space Studies Board.

The report warned that costs on WFIRST-AFTA could snowball if NASA needs to modify the donated telescope assemblies extensively, throwing the agency’s study of alternatives into sharper relief. The warning came only two weeks after NASA rolled out its 2015 budget request, which included $14 million to study not only WFIRST-AFTA but also so-called probe-class alternatives identified by NASA in 2012.

It is a long shot that Exo-S — which depends on technology never before flown in space — will supplant WFIRST-AFTA as the astrophysics division’s next big new start, one NASA official said.

“The WFIRST-AFTA mission is the primary choice of NASA Astrophysics,” Gary Blackwood, manager of NASA’s Exoplanet Exploration Program Office at the Jet Propulsion Laboratory in Pasadena, Calif., wrote in a March 7 email. But “if for any reason WFIRST-AFTA does not emerge from the study phase as such, then NASA Astrophysics will consider the possibility of the probe missions.”

Meanwhile, Blackwood said, NASA will also study pairing Starshade with “a 2.4-meter-class telescope, like AFTA.”

“The one nice thing about Starshade is that it is suitable for every telescope,” Ronald Polidan, manager of science and civil weather systems at Northrop Grumman’s Space Systems Division in Redondo Beach, Calif., said in a March 6 phone interview. “That’s one of the reasons we were drawn to it.”

Northrop Grumman has been working on Starshade since 2005, Polidan said. The company is the industry arm of a loose coalition that has been working on the technical aspects of Starshade development with NASA funding. Other team members include the University of Colorado, Boulder, and Princeton University.

Exoplanet detection depends on spotting the telltale flicker that occurs when a dim planet orbits a bright star — a process Polidan said is like “trying to image a firefly standing one centimeter away from a lighthouse beacon.”

Northrop Grumman has been attacking the challenge on two fronts: figuring out the best way to build a deployable, external occulter, and verifying that models produced by NASA-funded researchers in academia block distant light the way the real Starshade will have to do in space.

In August, Northrop Grumman successfully deployed a half-scale Starshade prototype about 20 meters in diameter. The model was based on the AstroMesh Reflector System the company has provided for spacecraft including London-based Inmarsat’s Alphasat I-XL, which launched in July 2013.

In May, Northrop Grumman plans to test a 60-centimeter Starshade prototype in the Nevada desert. 

“At one end there’s a light source, there’s a Starshade in the middle, and there’s a camera at the other end,” somewhere between 3 and 5 kilometers away from the light, Polidan said. 

“Over the next year or year and a half, we will be doing a whole series of tests on these, and when we leave our series of tests, we will have a very robust understanding of this,” Polidan told SpaceNews. “That’s pretty solid information. I would certainly be willing to sign up to launch something with all that knowledge.”

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Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...