WASHINGTON — NASA Administrator Jim Bridenstine said July 15 that, as NASA presses ahead with plans to return humans to the moon by 2024, he will not rule out a first human mission to Mars as soon as 2033.

Bridenstine’s comments, near the end of a 45-minute briefing with reporters about the 50th anniversary of Apollo 11 and the new Artemis program, are the latest sign of a renewed emphasis on human missions to Mars as a long-term goal for the agency in recent weeks.

“We are working right now, in fact, to put together a comprehensive plan on how we would conduct a Mars mission using the technologies that we will be proving at the moon,” he said when asked when a feasible date for a first human mission to Mars might be under NASA’s current exploration plan. “I am not willing to rule out 2033 at all.”

For several years, Mars exploration advocates have proposed human missions to Mars, either to orbit the planet or land on its surface, in 2033, citing a particularly favorable trajectory available that year. Those advocates have included Rep. Ed Perlmutter (D-Colo.), who frequently brings a “Mars 2033” bumper sticker to hearings of the House Science Committee.

However, a report prepared by the Science and Technology Policy Institute (STPI), as requested by Congress in the 2017 NASA authorization act, concluded a human Mars mission in 2033 was not feasible using NASA’s current architecture. “We find that even without budget constraints, a Mars 2033 orbital mission cannot be realistically scheduled under NASA’s current and notional plan,” STPI concluded in the report, made public in April after being delivered to Congress earlier in the year.

Bridenstine, in his comments, appeared to reject aspects of the STPI report. “I think there were assumptions in that report that maybe not everybody agrees with,” he said, such as the duration of surface stays. The STPI report, though, studied only Mars orbital missions for 2033 or later in the decade.

“I think there are alternatives out there that enable” a Mars mission in 2033, he said. “I am not saying that’s on the agenda. What I am saying is that NASA is looking at, given the fact that we have accelerated our path to the moon, how then does that accelerate our path to Mars? We’re looking at those trades and seeing what’s achievable.”

Bridenstine’s comments were the strongest sign to date that NASA remains committed to human missions to Mars as soon as feasible even as it pushes to accelerate a human return to the moon by 2024. While Bridenstine and the agency in general had stated that the moon was a “proving ground” for missions to Mars, that emphasis has grown since the June 7 tweet by President Trump criticizing NASA for talking about going to the moon. “They should be focused on the much bigger things we are doing, including Mars,” he wrote.

Both NASA and White House officials subsequently interpreted that tweet to mean that NASA’s near-term focus on returning humans to the moon shouldn’t overwhelm the long-term goal of humans to Mars. “I don’t think we always do a good job speaking to the larger vision that this is part of,” said Scott Pace, executive secretary of the National Space Council, at a conference a day after the president’s tweet. “What he’s doing is stepping back and expressing, I think, a very understandable impatience with how long all of that takes, and sometimes we miss the bigger picture.”

Bridenstine said in a July 12 interview on C-SPAN that he had spoken with the president since that tweet. “I talked to the president just a few short weeks ago and he said very clearly, ‘I know you’ve got to go to the moon to get to Mars, but talk about Mars,’” he said, noting that the president called Mars a “generational achievement that will capture the imagination” of the public. “He’s absolutely right, so we are going to continue talking about why we go to the moon: it’s the proving ground for the mission to Mars.”

In the July 15 media teleconference, Bridenstine said he last spoke with the president about three weeks ago, and Vice President Mike Pence, who chairs the National Space Council, about a week of two before that.

“The president and the vice president are very committed to going to the moon with the purpose of getting to Mars. We’re all in alignment on that,” he said.