WASHINGTON — NASA’s fiscal year 2021 budget request proposes cancelling an airborne observatory, a move that has surprised many astronomers but is also not the first time the project has faced termination.

The budget proposal, released Feb. 10, included the Stratospheric Observatory for Infrared Astronomy (SOFIA) among the programs slated for termination. SOFIA, which received $85.2 million in the fiscal year 2020 appropriations bill, would get $12 million in fiscal year 2021 to close out the program and mothball the observatory.

SOFIA is a Boeing 747 with a 2.5-meter telescope mounted in its fuselage. Equipped with a suite of infrared instruments, it carries out observations while at altitude, above most of the atmospheric water vapor that absorbs infrared light. The project is a joint effort with the German space agency DLR.

In its budget documents, the White House’s Office of Management and Budget (OMB) said that SOFIA’s scientific return did not justify its expense. SOFIA is currently the second most expensive astrophysics mission at NASA, behind only the Hubble Space Telescope, which received $98.3 million in 2019 and for which NASA requested $88.3 million in 2021. The James Webb Space Telescope, though, will be more expensive to operate — an estimated $172 million a year, according to the budget proposal — once it enters service after its 2021 launch.

OMB stated that SOFIA “has not delivered high quality data products or science on par with other large science missions. Future projections do not indicate a dramatic improvement in SOFIA’s scientific productivity in the next few years.” The high operating expenses of an airborne platform like SOFIA “results in low cost efficiency compared to most observatories.”

NASA offered similar language in its budget justification. “SOFIA’s annual operations budget is the second most expensive operating mission in the Astrophysics Division (after the Hubble Space Telescope), yet the science productivity of the mission is not on par with other large science missions,” it stated. “Dramatic improvement in SOFIA’s scientific productivity is not expected.”

A month earlier, though, NASA was singing a different tune. “Their plans for their extended mission include a lot of new initiatives that will increase SOFIA’s service to the community,” said Paul Hertz, director of NASA’s astrophysics division, during a SOFIA town hall meeting at the 235th Meeting of the American Astronomical Society (AAS) Jan. 7 in Honolulu. “The SOFIA team is working hard to implement those changes and make those improvements.”

Those improvements came from a pair of studies that NASA commissioned in 2018, one to examine the operations of the observatory and the other its science. Those studies concluded with recommendations on how to improve the efficiency of SOFIA.

“We want more discoveries per dollar,” said Jim Jackson, associate director for research at the SOFIA Science Center, which is run by the Universities Space Research Association (USRA), at that town hall meeting. “We want to optimize the value proposition of the observatory.”

That optimization, he said, includes automating more of the observing process and changing the cadence of flights, such as more flights that last eight hours instead of ten. Jackson said the shorter flights carry less fuel, which allow the plane to reach the stratosphere faster. “It makes much more sense to do five eight-hour flights than four ten-hour flights, because you spend more time, net, in the stratosphere.”

“Once we roll out this plan,” he concluded, “I am confident that we will be a premier facility for the coming decades.” That’s particularly true, he noted, for far infrared observations, which even JWST will not be able to perform.

USRA spokesperson Suraiya Farukhi said Feb. 13 there are no changes planned to SOFIA operations in light of the budget proposal, highlighting a number of scientific discoveries enabled by the observatory that were presented at last month’s AAS meeting. “The SOFIA team will stay the course and continue to provide the international community with high-quality data that addresses key topical science questions based on SOFIA’s unique capabilities.”

This is not the first time that NASA has proposed terminating SOFIA. In its fiscal year 2015 budget proposal, the agency also sought to terminate the observatory, just as it was set to begin its prime mission after an extended development cycle.

NASA leadership said then a lack of resources led it to propose cancelling SOFIA. “It turned out that we had to make very difficult choices about where we go with astrophysics and planetary science and Earth science, and SOFIA happened to be what fell off the plate this time,” Charles Bolden, NASA administrator at the time, said after the release of the budget.

Congress, though, rejected the proposed termination of SOFIA and funded the mission in fiscal year 2015 and subsequent years. It also included language in a 2019 spending bill preventing NASA from including SOFIA in a senior review of extended missions, just as SOFIA was completing its five-year prime mission. NASA instead conducted the science and operations reviews of SOFIA.

Among the observatory’s backers in Congress is House Minority Leader Kevin McCarthy (R-Calif.), whose district is adjacent to the Palmdale, California, facility that serves as SOFIA’s home base. McCarthy has not commented on the fiscal year 2021 budget proposal, but in a Dec. 17 statement about the passage of fiscal year 2020 appropriations bills, he included SOFIA funding as one of the “District and California priorities that McCarthy helped secure.”