If President Donald Trump's budget request becomes reality, NASA may need to shuffle some Red Planet missions, including developing a new project to map ice on Mars.

Trump and his administration sent Congress a budget request for the 2021 fiscal year in February. In its fine print, the Trump administration's 2021 budget request included a few major potential changes to NASA's Mars robotic exploration program.

It suggests reducing funding for the 2001 Mars Odyssey and Curiosity programs so drastically that these missions would essentially end, and it introduces a new "Mars Ice Mapper" orbital mission for the agency to consider.

NASA leadership discussed the budget request, which kicks off the annual budget process and lays out the administration's priorities, during a digital town hall held on March 20. But the request is just that, and Congress is responsible for determining final funding allocations.

"Remember the president's request is just a proposal; it's not an actual budget," Craig Tupper, NASA Resources Management Division Director, said during the town hall. "We do not act on that proposal."

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Related: Is the end near for Mars Odyssey? Trump's proposed 2021 budget could doom long-lived mission

Nevertheless, he said, the request does include some "funding holes" that NASA's science community would quickly recognize. Several of those were highlighted in the request summary, like canceling two Earth science missions and the WFIRST astrophysics telescope. But if all of the request's suggestions are retained in the final 2021 budget, Mars science will see big changes in the coming years.

On the loss side, two healthy missions, 2001 Mars Odyssey and the Curiosity rover, could see their ends come earlier than may be expected. "I know this was a tough one," Lori Glaze, head of planetary science at NASA, said during the town hall. "They're doing great science. We'd love to see them continue."

And Glaze emphasized that no one is prepared to write the two missions off just yet. "We are of course still looking to find ways to keep those going," she said.

But if NASA does end up retiring these spacecraft, the agency would likely need to launch something new. That's because Odyssey plays a key role as a communications relay satellite, sending messages between Earth and NASA's surface missions on the Red Planet. And the Mars mission introduced in the budget request represents a potential solution to that problem as well as a scientific project, Glaze said in the first agency comments about the idea.

The spacecraft, called Mars Ice Mapper, would, as its name implies, map ice on Mars, using a radar instrument that Canada has expressed interest in building and flying, Glaze said. But it could also act as a communications relay for landed missions, just like Odyssey does now, she added.

But the agency is still early in its evaluation of such a project, which Science Mission Directorate head Thomas Zurbuchen called "not a strategic-scale mission" during the event.

"There is funding there to begin a study to look at a potential concept to develop an ice mapper mission to Mars," Glaze said. "There's not really a lot more to say at this point."

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.