WASHINGTON — NASA plans to parcel out $25 million to study scientific instruments for a probe to Jupiter’s moon Europa, the agency said July 15.

Whether the proposed probe would go into orbit around the icy moon — which some scientists believe has an ocean of liquid water beneath an ice crust roughly 20 kilometers thick — or perform multiple Europa flybys from a Jupiter orbit is something NASA has yet to decide. 

Prospective instrument developers were told to consider both options in an announcement of opportunity NASA posted online as an amendment to the agency’s Second Stand Alone Mission of Opportunity Notice for planetary science proposals.

In the announcement, NASA said it wants to select as many as 20 instrument concepts by April 2015 for further study and then pick the eight most compelling in April 2016 to proceed into development. The selected instruments would have to be ready by 2021 for integration with the Europa probe, according to NASA’s announcement.

However, NASA has reserved the right to skip the initial yearlong instrument studies and pick eight concepts to proceed directly into development, the agency said. NASA will hold a preproposal conference in late July or early August; proposals will be due Oct. 17, NASA said.

At the White House’s behest, NASA is trying to figure out whether it is possible to do a scientifically worthwhile mission to Europa at about half the estimated cost of the agency’s leading concept, a multiple flyby mission known as Europa Clipper. As envisioned by NASA’s Jet Propulsion Laboratory in Pasadena, California, and the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland,  Clipper would fly by Europa about 45 times from a Jupiter orbit and would cost $2.1 billion, excluding launch, according to a NASA estimate that has been validated by the government-funded Aerospace Corp. of El Segundo, California.

Clipper was created after the White House in 2011 rejected a Jupiter Europa Orbiter concept NASA projected would cost almost $5 billion. Now the agency is mulling ways to cut Clipper’s price tag in half. The agency asked for ideas in early May and gave interested parties about a month to reply. NASA received six proposals for $1 billion Europa concepts and sent them to the Aerospace Corp. for evaluation, John Grunsfeld, associate administrator for science, said here in an interview after a Capitol Hill outreach event, The Lure of Europa, hosted by the Pasadena-based Planetary Society advocacy group.

“The results of the technical evaluations are being briefed to the Planetary Science Division by the end of July,” NASA spokesman Dwayne Brown wrote in a July 16 email.

A top planetary scientist who spoke at the Europa event July 15 questioned whether a month was long enough to lop $1 billion off a Clipper concept that took much longer to develop.

“We spent two years cutting the costs in half to come up with the Clipper concept,” Robert Pappalardo, JPL’s Europa Clipper preproject scientist, told reporters. “Others had about a month to try and cut the costs in half again. So we’ll see what they come up with.”

Clipper tracks closely with an eight-instrument flyby concept detailed in NASA’s July 15 announcement of opportunity. A six-instrument orbiter concept from the announcement, meanwhile, bears some resemblance to a hypothetical spacecraft Grunsfeld described in March during a panel discussion.

Grunsfeld said then a Europa orbiter fitted with a mass spectrometer similar to the Mars Organic Molecular Analyzer the European Space Agency plans to include on its 2018 ExoMars rover might allow scientists to take samples from water plumes thought to erupt periodically from beneath Europa’s ice crust. The sample science payload for the orbiter concept in NASA’s July 15 announcement included such an instrument, although prospective developers are free to propose types of instruments NASA did not mention in the announcement.

Evidence of water plumes around Europa was detailed in a December paper published by Lorenz Roth, an astronomer at the Southwest Research Institute in San Antonio. Roth’s paper was based on observations made with the Hubble Space Telescope.

NASA has not formally committed to any Europa mission, although the White House requested $15 million for 2015 to get the ball rolling with preliminary mission studies. 

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Correction: An earlier version of this story credited the image used to NASA.

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...