WASHINGTON — A day after NASA unveiled an amended budget request to support a human landing on the moon in 2024, the agency’s leader warned that if Congress provided less than the request it increased the risk of missing that deadline.

The revised budget request, released late May 13, seeks an additional $1.6 billion for NASA in fiscal year 2020. That funding would primarily go to accelerate development of the Space Launch System and Orion, and start work in lunar landers, with some funding for technology development and science missions to the Moon.

In a May 14 speech at the Humans to Mars Summit here, Bridenstine reiterated comments he made in a media teleconference the evening before that the $1.6 billion represented the agency’s estimate of what it needed to get moving on key programs in order to enable a human landing by 2024.

“The important thing is that we got what we requested,” he said. “We got what we requested in order to achieve 2024.” He noted that NASA would likely seek more money in future years, although the agency hasn’t identified how much more will be needed.

That $1.6 billion, he said, is at the “low end” of what’s needed in 2020. “If Congress comes in with a lower number, the probability of success goes down and the risk goes up,” he said. “Can we do it? I don’t know.”

Another complicating factor is that when the 2020 fiscal year starts Oct. 1, NASA and many other federal agencies will likely be operating under a continuing resolution (CR), a stopgap funding bill that limits spending to 2019 levels and usually prevents the start of new programs unless specifically authorized in the CR.

“There are opportunities, even in a CR, to make sure NASA gets what it needs in order to achieve the end state,” he said. “I would encourage members of Congress in a bipartisan way to think about that when they go forward.”

Speaking later at a NASA town hall meeting, Bridenstine reiterated that the $1.6 billion in additional funding for 2020 is enough to get started on a 2024 lunar landing, and hopes to win bipartisan support for it in Congress.

“I have heard criticism that somehow NASA didn’t work with Congress to do this, or the administration didn’t work with Congress, so it’s dead on arrival. That’s not the case,” he said. “This is good, out-of-the-gate first start, a very honest proposal from the administration that keeps us all together and moving forward in I think a bipartisan way.”

Few members of Congress have weighed in on the proposal. Many in the space industry are concerned that the proposal may face opposition because of the Office of Management and Budget sought to offset the increased spending for NASA, and smaller, unrelated increases to other agencies, by proposing to cut Pell Grant funding, used to help low-income students pay for college, by nearly $1.9 billion.

In a May 14 letter, the Association of Public and Land-grant Universities asked House and Senate appropriators to reject the proposal to pay for the NASA budget increase with Pell Grant funding. “A Pell Grant reserve rescission, as proposed by the administration, would be deeply misguided and contrary to the national interest,” Peter McPherson, president of the organization, wrote. “Choosing between providing additional funding for NASA and ensuring the long-term financial security of the Pell Grant program presents a false choice. We can and should support both.”

Bridenstine was one of several witnesses at a hearing May 14 by the Senate Commerce Committee’s space subcommittee on “The Emerging Space Environment,” but most of the questions focused on topics such as space traffic management and the proposed Space Force.

One committee member, Sen. Gary Peters (D-Mich.), sought assurances from Bridenstine that science programs at NASA would not be sacrificed in order to meet the 2024 goal.

Bridenstine provided those assurances, citing past failed human spaceflight initiatives that tried “cannibalizing one part of NASA to feed another part of NASA,” something he said the new approach avoided. “The $1.6 billion that we have now for going to the moon does not come from any part of NASA. It comes from outside of NASA.”

The budget amendment does have the support of Rep. Frank Lucas (R-Okla.), ranking member of the House Science Committee. “I commend the administration for putting forward an initial plan that is budget neutral and technically feasible and gives NASA the down payment to send Americans to the moon by 2024 without jeopardizing other critical missions,” he said in a May 14 statement. “As NASA acknowledges, more information and more funding will be needed to make this goal a reality, and we’ll be reviewing those details as they become available.”

At the Humans to Mars Summit, Bridenstine told an auditorium filled with Mars exploration advocates that the accelerated human return to the moon would also aid missions to Mars. “When we accelerate the lunar program, we are, by definition, accelerating the humans-to-Mars program,” he said.

In a panel discussion that followed at the conference, one expert was skeptical of that claim. Bhavya Lal of the Science and Technology Policy Institute led a recently published study, mandated by the 2017 NASA authorization act, that concluded that a 2033 mission to Mars was not feasible, with the earliest possible date for such a flight in 2037 or 2039.

She noted that, under the revised plan, NASA will be spending resources in the mid-2020s on lunar missions where, in the architecture studied in that report, NASA would instead be working on the deep space transportation systems needed for the Mars mission. It’s unlikely, she said, that NASA would be able to do both simultaneously.

“It is unclear to us, or at least to me, not having done a formal study, how going to the moon by 2024 accelerates Mars by 2033 or beyond,” she said.