WASHINGTON — NASA has accepted the recommendation of a review panel that it continue operations of a half-dozen astrophysics missions, including infrared and x-ray observatories and a retooled extrasolar planet mission.

In a June 9 letter, Paul Hertz, director of NASA’s astrophysics division, announced that NASA would extend six missions considered under the so-called “senior review” of missions that had already completed their primary missions, although some would face reduced funding.

“The report of the Senior Review panel makes clear that all of the missions proposing within the 2016 Senior Review are scientifically meritorious and deserving of continued funding and continued operations,” Hertz wrote in the letter.

The six missions included in the senior review were the Fermi Gamma-ray Space Telescope, Kepler, Nuclear Spectroscopic Telescope Array (NuSTAR), Spitzer Space Telescope, Swift Gamma-ray Burst Explorer and NASA’s participation in the European Space Agency’s X-ray Multi-Mirror Mission-Newton. The senior review separately considered NASA’s two flagship astronomy missions, the Chandra X-Ray Observatory and Hubble Space Telescope, as their continued operation was not in question.

The senior review panel, in a report released by NASA at the same time as Hertz’s letter, gave scores of “excellent” or “very good”, the highest two of five available ratings, for all the missions. The panel found no issues with any of the six missions that would raise any doubts about extending them for at least two more years.

“All the missions are highly meritorious by the absolute evaluations provided,” the report stated. “They constitute a balanced and highly productive portfolio, and a cost-effective leverage of substantial capital investment in flight hardware.”

The panel included assessments of each mission’s cost as part of the review, and concluded all were worth additional funding. “We strongly encourage NASA to find a way to continue all of these missions at their full funding level,” a point the report emphasized in bold type.

Hertz warned in his letter that might not be possible. “Although NASA will continue operations for all of the proposing missions, the current constrained budget conditions prevent NASA from being able to maintain current funding levels for all of the operating missions without unacceptable impacts on other parts of the astrophysics program,” he wrote.

Any funding reductions would be primarily limited to two missions. Hertz said the Fermi mission could continue with “reduced funding requiring further operation efficiencies.” He offered similar language for Spitzer, adding that the aging space telescope should focus on preparatory science for the James Webb Space Telescope.

Fermi and Spitzer were rated fifth and sixth, respectively, out of the six missions considered in the senior review, which the panel wrote in its final report was due in large part to their high costs. Fermi received $16.9 million and Spitzer $14.6 million in fiscal year 2015, the last year detailed spending breakouts for NASA’s astrophysics program are available.

The review panel, through, argued both missions should be continued. Fermi, the report stated, “represents the only significant access” to large portions of the gamma-ray spectrum for years to come. Spitzer, the panel argued, could make later observations of JWST more effective. “Making the JWST mission more efficient leverages the billions invested in JWST, and will allow JWST to achieve its maximum scientific potential,” the panel said in the report.

By contrast, Kepler, operating in an extended mission called K2, received overall scores of “excellent” by the panel, ranking it the highest of the six missions. “K2 represents an ideal example of why NASA continues to operate missions after their prime phase has been completed,” the panel concluded.

The news is a relief for the Kepler team, who two months ago were working to recover the spacecraft after it went into emergency mode. In a June 9 statement, Charlie Sobeck, Kepler and K2 mission manager, said it was likely a cosmic ray flipped a bit in the spacecraft’s computer, causing “multiple, random faults” that triggered the emergency.

“With the emergency behind us, and fuel to last us into the summer of 2018 or beyond, the news of the two-year mission extension was a welcomed vote of confidence in the team,” Sobeck said.

The senior review will be the last for both Kepler and Spitzer. Kepler’s mission will end when it runs out of fuel needed to maintain its orientation in space, while Spitzer, Hertz’s letter said, will shut down in early 2019, assuming a successful launch and checkout of JWST.

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...