Updated 8:30 p.m. Eastern.

WASHINGTON — The White House’s fiscal year 2020 budget request for NASA proposes to delay work on an upgraded version of the Space Launch System and would transfer some of that vehicle’s payloads to other rockets.

The proposal, released by the Office of Management and Budget March 11, offers a total of $21.02 billion for the space agency, a decrease of $480 million over what Congress appropriated in the final fiscal year 2019 spending bill signed into law Feb. 15.

A major element of the proposal is to defer work on the Block 1B version of the SLS, which would increase the rocket’s performance by replacing its existing Interim Cryogenic Propulsion Stage with the more powerful Exploration Upper Stage. The budget “instead focuses the program on the completion of the initial version of the SLS and supporting a reliable SLS and Orion annual flight cadence,” the OMB budget stated. The first SLS/Orion mission, without a crew, is now planned for the “early 2020s,” according to the budget, an apparent slip from the planned 2020 launch of Exploration Mission (EM) 1.

NASA had previously planned to use the Block 1B version of SLS to launch elements of its lunar Gateway, using a “co-manifesting” capability enabled by the rocket’s greater performance. Instead, according to the budget document, those components will be launched on “competitively procured vehicles, complementing crew transport flights on the SLS and Orion.”

“This approach would accelerate commercial lunar delivery capabilities critical to U.S. exploration objectives and speed up the timeline for lunar surface exploration,” the budget document stated. Overall, the budget seeks $1.78 billion for SLS, about $375 million less than what the program received in 2019.

In a briefing with reporters later March 11, Andrew Hunter, the deputy chief financial officer at NASA, said that the date of the EM-1 mission was under review. “We’ve had schedule challenges with the core stage,” he said. “We’re having an assessment underway to get to a realistic launch readiness date,” which he said would be done in the spring.

“Getting EM-1 and EM-2 launched as fast as technically possible is a prime objective of this budget, something that more money will not accelerate,” he said.

The decision to defer work on the SLS Block 1B would also appear to imperil plans to build a second mobile launch platform intended for use with that version of the rocket. Hunter said that, for now, work on that platform will continue since funding was specified for it in the fiscal year 2019 appropriations bill. “That is a recognized disconnect,” he said. “We’ll have conversations with Congress about that.”

The budget proposal would also remove one non-exploration payload from the SLS manifest. The proposal offers nearly $600 million for the Europa Clipper mission, enabling a launch in 2023. However, NASA would instead seek to launch the mission on a commercial launch vehicle rather than SLS, a move it claims “would save over $700 million, allowing multiple new activities to be funded across the Agency.” The fiscal year 2019 budget request also proposed a commercial launch of Europa Clipper, but Congress placed into law in the final funding bill the requirement to use SLS for that mission.

NASA Administrator Jim Bridenstine made no mention of the proposed deferral of the SLS Block 1B in remarks March 11 at the Kennedy Space Center to discuss the agency’s budget request. “It is a critical piece of the architecture that enables us to deliver reusability to the moon,” he said of SLS. “This is a transformational strategic capability for the United States of America.”

Other cuts and new programs

The budget proposal includes another effort to cancel other agency programs. The budget proposal seeks no funding for the Wide-Field Infrared Survey Telescope (WFIRST), the next flagship astronomy mission after the James Webb Space Telescope. That mission was also proposed for cancellation in the 2019 budget proposal but funded by Congress.

The budget requests to end funding for the Office of STEM Engagement, the new name of the Office of Education. The White House sought to close NASA’s education office in the 2018 and 2019 budget requests, and both times faced strong bipartisan criticism of the move. The proposal seeks to cancel two unnamed Earth science missions, again paralleling proposals in the 2018 and 2019 budget requests ultimately rejected by Congress. NASA budget documents identified those Earth science missions as CLARREO Pathfinder and PACE, which were also targeted for cancellation in the 2018 and 2019 requests.

NASA officials said that cancelling WFIRST would save $383 million, while cancelling the CLARREO Pathfinder and PACE would save $127 million. The Office of STEM Engagement received $110 million in the fiscal year 2019 spending bill.

Bridenstine didn’t discuss those proposed cuts, emphasizing instead the continued support for the James Webb Space Telescope and Earth science programs. “It has been a challenge for me as your NASA administrator to go up to the Hill and talk about the James Webb Space Telescope,” he said, because of its cost and schedule overruns. “This administration is committed to the James Webb Space Telescope and we have bipartisan support for the James Webb Space Telescope.”

The budget does include some new initiatives. One seeks $363 million to start development of large lunar landers that would deliver cargo, and ultimately crews, to the surface of the moon. NASA recently requested proposals for studies from industry on the development of such landers.

The proposal makes no reference to ending direct federal funding of the International Space Station, as proposed in the 2019 request. “By 2025, the Budget envisions commercial capabilities on the International Space Station as well as new commercial facilities and platforms to continue the American presence in Earth orbit,” the document states.

“We’re obviously not going to shut down the space station, but the intent is that the federal government does not continue operating it and that we are building this commercial program to look at opportunities for commercial industry and partners to take over the operations,” Hunter said.

The proposal does include funding for a new Communications Services Program that would purchase commercial communications services to return data from NASA science missions, but start at only $3 million in 2020.

The budget proposal also includes funding for a Mars sample return mission that would collect the sample cached by the Mars 2020 rover and return them to Earth. That mission would launch as soon as 2026, according to a fact sheet issued by NASA. Hunter said that the budget proposal includes $109 million for future Mars mission formulation work, which would primarily go to planning for Mars sample return. That funding wedge would grow to about $400 million a year by 2023 and 2024.

“I want everybody to know that NASA’s budget request is very good,” Bridenstine said near the end of his speech, citing bipartisan support in Congress. “We’re going to be able to accomplish more than we’ve ever been able to accomplish before because of the administration’s support.”