The astronauts onboard Artemis II were “almost poets”, Nasa’s administrator, Jared Isaacman, declared on Friday, referring to their inspiring words as they swung above the lunar surface.

They were, he said, “ambassadors for humanity” as they became the first humans to travel to the moon and return safely to Earth since 1972, on a mission that broke a distance record.

Meanwhile, the mood at the Johnson Space Center in Houston on Friday night was one of jubilation and celebration as the Orion capsule made a textbook splashdown in the Pacific Ocean after its 10-day lunar odyssey.

Nasa astronauts Reid Wiseman, Victor Glover and Christina Koch, plus Jeremy Hansen of the Canadian Space Agency, will give a press conference later on what they saw and experienced.

“The mission is over but the melody lingers on,” the Nasa TV commentator Derrol Nail noted.

In truth, the successful conclusion of the US space agency’s first crewed mission to the moon in more than 50 years represented unquestionably its biggest achievement since the Apollo generation.

To do again what no other country has managed to accomplish once leaves the US with a significant advantage in the new space race with China for the next moon landing and construction of a permanent habitat there.

Yet once the celebratory flags stop waving, and the engineers of Artemis refocus their attentions on the challenges ahead, it is hard to escape the notion that the biggest hurdle to the realization of the country’s grand ambitions in deep space lies within.

Even as Integrity, the mission moniker for the Orion capsule of Artemis II, ascended into the heavens days ago, Donald Trump was announcing his intention to slash Nasa’s budget by 23%, including a 46% cut for space science initiatives. And the Artemis program that has run years behind schedule and billions of dollars over budget offers no guarantees that the next, far harder stages will run as smoothly.

“The path to the lunar surface is open, but the work ahead is greater than the work behind us. It always will be,” Nasa’s associate administrator Amit Kshatriya said on Friday at a post-landing press conference in Houston.

“Fifty-three years ago, humanity left the moon. This time we return to stay. Let us finish what they started.”

No space analyst will discount the magnitude of what Artemis II has brought to the US human spaceflight program. Undoubtedly, the vision of a permanent lunar base has moved closer with the knowledge that the US possesses, finally, another proven rocket and capsule assembly that can sustain human life beyond lower-Earth orbit.

But there is also the president, who expressed in a post to his own Truth Social on Friday how proud he was of the “great and very talented” crew while making no mention of his desire to impose “extinction-level” cuts to the agency he purports to value.

Isaacman said he supported the White House desire to strip a further $6bn in funding from his agency, insisting that the levels “are sufficient” to meet “high expectations and deliver on all mission priorities”.

But Casey Dreier, chief of space policy at the Planetary Society, said Isaacman’s argument made no sense.

“The administrator is part of the administration, and the budget document is an official policy statement of the administration, so he has to be onboard,” he said.

“But it’s discordant. The budget itself is seemingly contradictory with a number of statements that Nasa leadership said a few weeks ago at the Ignition event. It adds more confusion to this situation than clarity and is a baffling piece of political ideology from an alternate universe in which they didn’t suffer an overwhelming defeat of that proposal just months ago.”

Dreier was referring to a rare display of bipartisanship in Congress in January that rejected an almost identical proposal by Trump for Nasa’s 2026 budget, and looks likely to do so again for 2027.

“I call it a copy-paste budget, and I’m not really exaggerating because some of the highlights include how they would find savings by canceling the Mars sample return, which was canceled last year and is done,” he said.

“There’s no more. You can’t double-cancel it. It mentioned two [other] programs which ended last year. There are major errors such as requesting funding for both the James Webb and Hubble space telescopes because they forgot to change the cut and paste, right?

“It is a sloppy request in, again, an alternate universe where they’re acting like their budget proposal occurred rather than being overturned heartily.”

Dreier said the experience of Artemis II was spoiled by Trump’s demands. “It reminded me how exciting and astonishing this ability is to just go somewhere new and explore it, and how much I’ve missed that in our society, at least with human spaceflight,” he said.

“Simultaneously, it was an experience marred by the fact that the agency that is tasked with keeping these astronauts safe had proposed to be functionally dismantled in one of the more tasteless releases of a draconian budget requested in modern times.

“It was a real insult to the team, to the astronauts, and to the agency itself on achieving the most difficult thing anyone has done in spaceflight, to propose dismembering the agency to such a degree.”

Despite the reservations, Nasa will celebrate long and hard its achievement in bridging a near 54-year gap from Earth to the moon, and is already looking ahead to Artemis III, scheduled for next year, which will test human lunar landing systems.

“The childhood Jared right now can’t believe what I just saw, I mean I’ve almost been waiting my whole lifetime to see this,” Isaacman told Nasa TV from the crew recovery ship USS John P Murtha in the Pacific Ocean.

“We are back in the business of sending astronauts to the moon, bringing them back safely, and setting up a series more. This is not a once in a lifetime, which you hear sometimes around here. No, it’s not. This is just the beginning. We are going to get back into doing this with frequency, sending missions to the moon until we land on it in 2028 and start building our base.”

Dreier was keen to point out that his criticism about the White House budget proposal did not affect his admiration for the Artemis II crew’s achievements.

“It’s an incredibly important turning point that we have the hardware to take people into deep space and back,” he said.

“It’s kind of an interesting triumph for the classic aerospace contracting model, very expensive, but it has worked, and now we’re going to place the rest of the bet on the commercial systems to follow through on that timeline.

“If this didn’t work correctly we wouldn’t, there’s no feasible way we’d be landing on the moon in the next few years. Obviously, there’s a lot to go and we can’t underestimate how difficult this is. We just have to be extremely humble about how few times this has happened in human history.”