Astronauts work on the International Space Station in 2006. (AP/AP)

The White House is proposing a $19.9 billion budget for NASA, a nearly $400 million increase over the current budget, as part of a strategy to further fuel entrepreneurial endeavors and take the first steps to return to the moon.

But its 2019 budget proposal, released Monday, did not outline a concrete plan or timeline to travel to the lunar surface, which the Trump administration has said is one of its top priorities for NASA. The spending plan also proposed ending funding for the International Space Station after 2024, and privatizing the orbiting laboratory to free up funds for deep space exploration.

In a statement to The Washington Post, Scott Pace, the executive secretary of the reconstituted National Space Council, said the administration plans to work with industry and international partners to find away to transition the station into private hands.

“With seven years with which to plan a transition to a different operational model, the United States will again demonstrate our role as the indispensable spacefaring nation,” Pace said. “The transition of low Earth orbit from an environment dominated by the government to one that flourishes with commercial, international, and government partnerships is not only possible, but necessary for continued U.S. leadership.”

An official with the European Space Agency, a partner on the space station, said he hadn’t yet seen the proposal so couldn’t comment. Some officials said it could be tricky for the United States to get out of the station’s international treaties. Another roadblock is going to be Congress, where key members have already said they would not allow support for the station to be terminated before its useful life is over.

“The administration’s budget for NASA is a nonstarter,” Sen. Bill Nelson (D-Fla.) said in a statement. “Turning off the lights and walking away from our sole outpost in space at a time when we’re pushing the frontiers of exploration makes no sense.”

The White House isn’t planning on abandoning the station outright, and is looking to keep a robust presence in low Earth orbit in partnership with industry and other countries, according to an administration official not authorized to speak publicly about the plan. The budget calls for $150 million for a program to help industry create space habitats that could be used in place of the space station, according to the budget request released Monday.

The official said the administration is trying to avoid the problem that plagued the space shuttle retirement. When the shuttle was retired in 2011, NASA had no way of flying its astronauts to the space station, and has had to rely on Russia for rides to space. SpaceX and Boeing are now under contract from NASA to build spacecraft capable of flying humans, but those first flights won’t come until later this year or next, leaving the U.S. government without the ability to fly people for at least seven years.

“The notion that we would walk away from LEO [or low Earth orbit] and the space station is not accurate,” the official said. “We know the space station is going to eventually end. Rather than putting ourselves in the situation with shuttle, where we had no way to get to LEO, we want to start planning for that transition now.”

The United States’ international partners on the station “are one of the most important pieces of the station and how it functions,” the official said. “We believe that opening up options and different models also means opening up opportunities for additional partners and additional ways to expand our international involvement in low Earth orbit. Imagine a scenario where a company says we have a business plan, we’d like to partner with the Japanese government and the Europeans to do these types of experiments.”

The official said that under commercial control, NASA would become another customer, so “instead of owning the building, we would rent a couple of floors.”

In its budget document, the White House said it plans to partner with industry “to land robotic missions on the surface of the moon in the next few years, paving the way for a return of U.S. astronauts — this time not just to visit, but to lay the foundation for further journeys of exploration and the expansion of the U.S. economy into space.”

The budget proposal “really reflects the administration’s confidence that America will lead the way back to the moon and take that next giant leap,” NASA acting administrator Robert Lightfoot said in a speech Monday at the Marshall Spaceflight Center in Alabama.

Nelson, the U.S. senator, expressed concern about plans beyond the moon.

“If we’re ever going to get to Mars with humans on board and return them safely, then we need a larger funding increase for NASA,” he said.

The proposed budget also calls for the termination of the $100 million Office of Education at NASA “redirecting those funds to NASA’s core mission of exploration.” And while it supports the development of the $8.8 billion James Webb telescope, the budget calls for the termination of the WFIRST space telescope, which NASA planned to help scientists better understand dark matter and dark energy.

The budget would provide $54.2 million for public-private partnerships to help develop manufacturing technologies in space, such as 3-D printing.