This week, as part of the process to develop a budget for fiscal-year 2026, the Trump White House shared the draft version of its budget request for NASA with the space agency.

This initial version of the administration’s budget request calls for an approximately 20 percent overall cut to the agency’s budget across the board, effectively $5 billion from an overall top line of about $25 billion. However, the majority of the cuts are concentrated within the agency’s Science Mission Directorate, which oversees all planetary science, Earth science, astrophysics research, and more.

According to the “passback” documents given to NASA officials on Thursday, the space agency’s science programs would receive nearly a 50 percent cut in funding. After the agency received $7.5 billion for science in fiscal-year 2025, the Trump administration has proposed a science top-line budget of just $3.9 billion for the coming fiscal year.

Detailing the Cuts

Among the proposals were a two-thirds cut to astrophysics, (down to $487 million), a greater than two-thirds cut to heliophysics (down to $455 million), a greater than 50 percent cut to Earth science (down to $1.033 billion), and a 30 percent cut to Planetary science (down to $1.929 billion).

Although the budget would continue support for ongoing missions such as the Hubble Space Telescope and the James Webb Space Telescope, it would kill the much-anticipated Nancy Grace Roman Space Telescope, an observatory seen as on par with those two world-class instruments that is already fully assembled and on budget for a launch in two years.

“Passback supports continued operation of the Hubble and James Webb Space Telescopes and assumes no funding is provided for other telescopes,” the document states.

Other significant cuts include ending funding for Mars Sample Return as well as the DAVINCI mission to Venus. The budget cuts also appear intended to force the closure of Goddard Space Flight Center in Maryland where the agency has 10,000 civil servants and contractors.

The Passback Process

The cuts are in line with what Ars Technica exclusively reported last month, that the Trump administration was considering a massive 50-percent cut to NASA’s science programs. Publicly, some officials downplayed these concerns. As recently as this week, NASA’s acting administrator, Janet Petro, characterized this reporting as “rumors from really not credible sources.”

However, science policy experts have been more alarmed, characterizing such cuts as an “extinction level” event for what is seen as the crown jewel of the space agency. Nearly all of NASA’s most significant achievements over the past 25 years have been delivered by the science programs, including feats such as the Ingenuity helicopter flying on Mars, New Horizons swooping by Pluto, and Cassini’s discovery of water plumes on Enceladus.

This passback document represents just the opening salvo of the process to establish a federal budget for fiscal-year 2026, which begins on October 1 of this year. The budget is produced by the White House Office of Management and Budget, which is overseen by Russell Vought, who has long made his anti-science budgeting priorities clear through his Center for Renewing America.

The Trump administration nominee to lead NASA, private astronaut Jared Isaacman, said during a confirmation hearing this week that he strongly supported NASA’s science programs. It is unlikely that Isaacman was involved in drafting this document, as he has not yet been confirmed by the US Senate. Nominees, typically, are excluded from policy prior to confirmation.

After receiving passback documents, NASA usually has 72 hours to review the materials and then submit appeals and justification for changes. Any modifications are then incorporated into a final document that becomes the “President’s Budget Request” for the next fiscal year. It is not clear when the Trump administration plans to release this budget request, a public document. It could happen within the next four to six weeks.

Congress Will Likely Fight Back

Following this, the White House will work with Congress to actually set the budget. The US House and Senate each have separate appropriations committees that consider (or not) the White House priorities in establishing a final budget that the president must then sign into law. Fierce opposition to some of these NASA cuts is likely in Congress.

“This massive cut to NASA Science will not stand,” Representative George Whitesides, a California Democrat, told Ars. “For weeks we have been raising the alarm about a rumored 50 percent cut to NASA’s world-leading science efforts. Now we know it is true. I will work alongside my colleagues on the Science Committee to make clear how this would decimate American leadership in space and inflict great damage to NASA centers across the country.”

One concern, however, is that should the budgeting process be delayed—as is often the case with the federal budget—the White House could force agencies to make operational plans based on the president’s budget request once the new fiscal year begins on October 1. Again this will depend on negotiations with Congress, but, using a process called impoundment, some Trump officials believe it may be possible to turn the budget request into an actual budget for all intents and purposes.

This story originally appeared on Ars Technica.