WASHINGTON — Astronomers are pushing back against plans by NASA to cut the budgets of two venerable space telescopes, arguing that the cuts to one of them could jeopardize the future of X-ray astronomy in the United States.

NASA’s fiscal year 2025 budget proposal, released March 11, proposed reducing the operating budgets of two of its remaining original “Great Observatories” space telescopes. The proposal offered a modest reduction in the Hubble Space Telescope, from $98.3 million in the final fiscal year 2024 spending bill to $88.9 million.

The cuts to the Chandra X-Ray Observatory, though, are more significant. That mission, which received $68.3 million in 2023, would see its budget cut by 40% to $41.1 million in the request. The budget proposal also projected further reductions after 2026, falling to just $5.2 million by fiscal year 2029.

NASA, in its budget request, argued that Chandra’s performance has been degrading over time. “This makes scheduling and the post processing of data more complex, increasing mission management costs beyond what NASA can currently afford,” the budget proposal stated. “The reduction to Chandra will start orderly mission drawdown to minimal operations.”

Astronomers took sharp issue with that characterization of the nearly 25-year-old spacecraft. In a March 19 open letter, Patrick Slane, director of the Chandra X-Ray Center, noted that the mission has been dealing with issues like increasing temperatures for many years, and have incorporated measures to deal with them into existing operations and software. Thus, he concluded, “there is nothing about Chandra’s evolving temperature behavior that makes ‘post processing of data more complex.’”

The budget proposal, he argued, would result in a “closeout” of the mission rather than reduced operations. “The funding levels provided in the new budget plan are consistent with levels for these closeout activities, but lower than can accommodate operation of the Chandra science mission; the minimal operations referred to in the budget document would actually be decommissioning activities.”

At a March 20 meeting of NASA’s Astrophysics Advisory Committee, or APAC, agency officials defended the proposed cuts, saying overall budget pressures are forcing them to find ways to reduce the costs of operating both Chandra and Hubble.

“We don’t want to cancel Chandra,” said Nicola Fox, NASA associate administrator for science, at the meeting. “What we’re looking for is more efficient ways of operating these missions so we can continue them moving forward.”

NASA is planning to convene what officials have called a “mini senior review” to examine ways to operate both missions with smaller budgets. “Are there ways we can maintain scientific productivity with significantly different operating budgets?” said Mark Clampin, astrophysics director at NASA Headquarters, at the APAC meeting. “We cannot, with the budget that we have right now in ’25 or the outyears, fund these missions at the level they’ve been funded at in the past.”

That effort is formally known as an Operations Paradigm Change Review, which will be handled differently than traditional senior reviews that evaluate whether spacecraft past their prime mission should be extended. Eric Smith, associate director for research and analysis in NASA’s astrophysics division, said at the meeting that is driven by a schedule that requires the review be done by the end of May to support planning for the agency’s fiscal year 2026 budget request.

He said the missions will have to submit options for operating Chandra and Hubble that fit within the funding profile in the budget proposal. They will, though, be able to also offer options with different funding requirements.

“The budgets mandate that these missions work differently than they have in the past. There will be science impacts,” he acknowledged. “I don’t think we’re under any illusion you can have the budgets that are there and things just keep going the way that they have.”

That could mean, for example, turning off some instruments. “Do we, in the age of Webb, want to continue operating a near-IR camera on Hubble?” offered Clampin as a hypothetical example of trades the missions and the review panel will consider.

He said that analysis is best done by the review panel and the missions themselves, which best know the capabilities of the telescopes and the science they can perform. “We just don’t have time to engage in a big, widespread poll of the science community,” he said.

However, both members of APAC as well as others in a public comment period expressed concerns about the effects of the proposed cuts on both missions, particularly Chandra, which some argued could significantly hurt X-ray astronomy in general.

Dave Pooley of Trinity University, a member of the Chandra Users’ Committee, noted that X-ray astronomers in the U.S. rely on Chandra funding to carry out their research. “Sudden budget cuts of this magnitude send a signal that X-ray astrophysics in the U.S. is in an extremely precarious situation,” he said. “It is unclear how and even if X-ray astrophysics in the U.S. will survive these cuts.”

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...