WASHINGTON — A nonprofit organization says it is continuing efforts to develop a space telescope to search for near-Earth asteroids despite fundraising challenges and a recent NASA decision to terminate a cooperative agreement.

The Mill Valley, California-based B612 Foundation announced plans in 2012 to develop Sentinel, a space telescope with an estimated cost of $450 million, to look for asteroids that could pose an impact risk to the Earth. The foundation planned to raise the money privately, seeking donations in an approach it likened to raising money for a museum or university building.

When B612 announced its plans for Sentinel, it had a Space Act Agreement with NASA to support the project. The agreement, signed by NASA in May 2012, gave B612 access to NASA’s Deep Space Network to communicate with Sentinel after launch, and included the agency in planning of Sentinel observations and data analysis.

B612, in turn, agreed to deliver Sentinel data to the Minor Planets Center, a clearinghouse of observations of asteroids. The foundation also agreed to coordinate with NASA before making any public announcements of “significant findings” from the mission. The agreement included no exchange of funds between NASA and B612.

However, NASA recently terminated that agreement. NASA spokesman David Steitz said Oct. 16 that NASA sent a formal notice terminating the agreement to the foundation on Aug. 13 after six months of discussions. “NASA terminated our Space Act Agreement with B612 because the foundation failed to meet agreement milestones,” he said.

The timing of the decision, Steitz said, was linked to NASA annual budget planning activities. He estimated that NASA spent about $200,000 and 500 hours of NASA civil servant time supporting its role in the agreement.

NASA officials had publicly raised questions about the future of the agreement with B612 for more than a year. At a July 2014 meeting here of a NASA advisory group called the Small Bodies Assessment Group, Lindley Johnson, program executive for NASA’s near-Earth objects program, said the agency was re-evaluating the agreement.

“It’s under review right now,” Johnson said during a discussion at the meeting about Sentinel. That review was prompted by the lack of technical and schedule progress B612 had reported on Sentinel at that time. “None of the milestones have been met to date,” he said.

The agreement included a series of “gates” where NASA and B612 would review the technical ability of Sentinel to meet its science goals. If B612 could not meet one of those gates, NASA would “determine whether or not to proceed with this agreement,” it stated.

The agreement also included a schedule for Sentinel, including a preliminary design review in October 2013, a critical design review in October 2014, and launch in December 2016. B612 has not reported meeting any of those milestones.

That lack of progress appears to be linked the foundation’s difficulties raising money. B612 spokeswoman Diane Murphy declined to state in an Oct. 7 interview how much money B612 had raised for Sentinel to date. However, according to documents filed with the U.S. Internal Revenue Service, the foundation reported revenue of a little more than $1.6 million in 2013, the most recent year currently available, and approximately $1.2 million in 2012.

Moreover, the foundation spent most of that revenue on expenses. The foundation reported expenses of more than $1.5 million in 2013, including salaries for two employees and for consultants. According to that tax filing, the foundation had less than $1 million in total assets as of the end of 2013.

Despite the terminated NASA agreement, Murphy said B612 planned to press ahead with Sentinel. “It doesn’t affect our business efforts at all until we have use for that network, and then we will re-approach NASA at that time,” she said, referring to NASA’s Deep Space Network.

“The status of the Space Act Agreement in no way changes the resolve of the B612 Foundation to move forward,” Ed Lu, a former NASA astronaut and chief executive of the foundation, said in an Oct. 7 statement. “Funding for large private space projects has historically been difficult, both to secure and to predict when full funding will occur. Sentinel is no different.”

A complicating factor in B612’s plans is a separate project called NEOCam to develop a space telescope to look for near-Earth asteroids. The concept, developed by a team at the Jet Propulsion Laboratory, was one of five proposals selected by NASA in September for additional study in the latest round of the agency’s Discovery program. NASA expects to select one or possibly two proposals for full development next year.

Murphy said B612 would be open to cooperating with NEOCam or any other mission to look for near-Earth asteroids. “The only reason we announced Sentinel was because no one else was solving this critical challenge,” she said. “If another entity in the meantime creates this asset, we will fully support them.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...