Even Trump’s space policy adviser for his campaign and transition says getting a man or woman on the face of Mars by 2024 is virtually impossible.

“I don’t think you’ll get there [to Mars],” former Pennsylvania Rep. Bob Walker said in an interview about the possibilities under the Trump White House. “I do think that we will probably have a flight to the moon, an Apollo 8-type flight where you go up and go around the moon in a fairly short period of time.”

A NASA official who served under former President Barack Obama shared Walker’s prediction. “I think things could go very well for going to the moon, which I think is more likely to be a Trump agenda,” said Lori Garver, Obama’s deputy NASA administrator.

During his first six months in office, Trump has laid out an ambitious — if non-specific — space agenda.

Beyond his promises on Mars, Trump has reinstated the National Space Council, a coordinating body that was first created under a different name during the Eisenhower administration, but has been dormant since 1993 after infighting doomed the entity. He’s also talked up the potential for the private sector to help advance space travel in the near future.

But there are plenty of other signs that cast doubt on Trump’s dedication to ambitious leaps in space exploration.

Trump still hasn’t named a NASA administrator — one of three top NASA posts that have yet to be filled.

Rep. Jim Bridenstine (R-OK) is the most prominent contender, but has been for months. Current acting administrator Robert Lightfoot is also a possibility, according to Walker. A spokesperson for Bridenstine’s office did not respond to a request for comment.

The space council has also seen slow progress. Pence said at the Kennedy Space Center that he hoped to have the space council’s first meeting before the end of the summer. But Marc Lotter, the vice president’s press secretary, said a date for that meeting has yet to be set.

The slow progress of the council and the NASA appointments worries some in the space community, who wonder how Trump is going to meet his space exploration goals.

“I think there is a growing impatience with getting started with setting a direction of the space program that reflects Mr. Trump’s views,” said John Logsdon, founder and former director of George Washington University’s Space Policy Institute.

Logsdon said the space policy community is encouraged by signals coming from the White House, but with little policy specifics announced, any optimism is cautious.

“I think the community wants to give the council a chance, wants to give Mr. Trump a chance,” Logsdon, who authored an extensive historical essay on council in January, said. “Everything he’s said so far, at least in terms of civilian space anyways, has been really positive. I think the community wants the words backed up by actions.”

Trump also has yet to reckon with the harsh realities that would make it challenging to greatly accelerate NASA’s “Journey to Mars” program that currently has astronauts reaching the vicinity of Mars in the 2030s.

In a call with NASA astronauts in April, Commander Peggy Whitson explained to the president that putting a human on Mars by 2024 is a longshot.

“Unfortunately, spaceflight takes a lot of time and money, so getting there will require some international cooperation to get it to be a planet-wide approach, just because it is a very expensive endeavor,” Whitson told Trump.

Logsdon called Trump’s notion that the country could go to Mars ahead of schedule “nonsense.”

The White House press office did not immediately respond to a request for comment.

Trump’s space policy — as described by Walker, Pence and several Republicans on the House Subcommittee on Space — will center around increasing the role of the private sector, with the government entering more partnerships with companies like SpaceX and Boeing.

But using the private sector to accelerate NASA’s schedule has its challenges. Walker said the U.S. will no longer have to depend on Russia rockets — which cost NASA roughly $80 million a seat — to get astronauts to the International Space Station, as Boeing and SpaceX test commercial crew vehicles.

But NASA thought in 2011 that the commercial space industry would be able to launch astronauts to the station by 2015, according to a 2016 audit.

Even with the private sector involved, space policy experts say the government would have to spend more money—and increase NASA’s budget—to get to Mars sooner.

However, Trump’s budget proposal for the 2018 fiscal year has NASA at $19.1 billion, which leaves the space agency’s resources relatively unchanged from the last few years. Though the agency warmly praised the budget, there are no major changes that indicate the Journey to Mars program will be accelerated.

“There’s nothing that we’re spending on right now that would preclude a policy that we’re going to the moon and then going to Mars,” said Andrew Aldrin, director of the Buzz Aldrin Space Institute. “I would argue that what we’re spending money on is less than optimal than what we would need to go to Mars.”

Garver said the first year of a new administration is an information-gathering year, and that like the Obama administration, the Trump White House’s second budget request would reflect more substantive policy decisions.

And if the administration decides to rapidly accelerate the Journey to Mars program by nearly a decade, the U.S. might have to end its commitment to the International Space Station.

The American portion of the space station is funded through 2024, but the U.S. will soon have to decide whether to stay or redirect those resources—roughly $3 billion—elsewhere if it decides to go to Mars in the near future.

“If we maintain the International Space Station we will not have the funding for deep space exploration,” Rep. Brian Babin (R-Texas) said of choosing Mars over the space station. “We need to make plans. I just don’t think we can do both.”

Babin, who chairs the House Subcommittee on Space, said members have varying views on staying with the International Space Station past 2024 but nearly everyone wants to go back to the moon and eventually to Mars.

Meanwhile, Garver says the U.S. is likely to stay a part of the International Space Station after Scott Pace was appointed as executive secretary to the space council.

“He’s been a supporter of commercial space, but also a supporter of status quo large programs, and would likely keep those as well,” Garver said.

In the same April conversation with NASA astronauts, Trump said “we’ll have to speed that up a little bit,” to get to Mars under his administration. However, few outside of the former real estate mogul himself have seemed to agree it would happen.

Walker, along with White House adviser Peter Navarro, helped craft space policy during the campaign, which was summed up in an op-ed in October entitled “Trump’s space policy reaches for Mars and the stars.” With Mars still scheduled for the 2030s, experts and one of those same advisers say the U.S. will still be reaching for Mars at the end of the Trump era.

“I think they’re pronouncements that are aspirational and the president likes to make those kinds of statements,” Garver said of going to Mars under Trump. “It would be best for NASA if the goal came with a why, a purpose … I don’t think a lot more thought has gone into it.”