If you're skeptical that NASA can put boots on the moon by 2024 , you're not alone.

During a hearing of the space subcommittee of the U.S. House of Representatives' Science, Space and Technology Committee on Wednesday (Sept. 18), multiple representatives voiced concerns about the agency's progress toward the ambitious 2024 lunar-landing goal. And one of the key witnesses, Ken Bowersox, NASA's acting associate administrator for human exploration and operations, didn't exactly put their deadline doubts to rest.

When Rep. Bill Posey, R-Fla., asked how confident he was that NASA would meet the 2024 target, for example, Bowersox responded, "I wouldn't bet my oldest child's upcoming birthday present or anything like that."

Related: Home On the Moon: How to Build a Lunar Colony

The 2024 target is a good thing, Bowersox added, saying that aggressive goals help focus the agency's efforts and attention. But he stressed that meeting the deadline is not the agency's main objective.

"We're going to do our best to make it. But, like I said, what's important is that we launch when we're ready, that we have a successful mission when it launches," he said.

"And I'm not going to sit here and tell you that, just arbitrarily, we're going to make it," said Bowersox, a former NASA astronaut. "We have to have a lot of things come together to make it happen. We have to get our funding, we have to balance our resources with our requirements, and then we've got to execute it really well. And so, there's a lot of risk to making the date, but we want to try to do it."

NASA is doing this work via a lunar-exploration program called Artemis , which envisions using the moon as a steppingstone to the ultimate human-spaceflight destination: Mars.

If all goes according to plan, NASA will build a small moon-orbiting space station called the Gateway in the early 2020s. Gateway is key to the overall Artemis effort, because it will serve as a hub for surface missions. Landers, both crewed and uncrewed, will depart from the Gateway to the lunar surface and return to the ministation when their work on the ground is done. Astronauts will also operate moon rovers from this orbital perch, NASA officials have said.

The space agency aims to land two astronauts — including the first-ever female moonwalker — near the lunar south pole in 2024 and establish a sustainable, long-term presence on and around the moon by 2028.

This latter date was the original target for the first crewed lunar landing since the Apollo era. But in March, Vice President Mike Pence moved the timeline up four years .

"Urgency must be our watchword," Pence said at the time, invoking a space race with Russia and China. "The United States must remain first in space in this century as in the last, not just to propel our economy and secure our nation but, above all, because the rules and values of space, like every great frontier, will be written by those who have the courage to get there first and the commitment to stay."

NASA plans to achieve the Artemis goals using the Orion capsule and a huge rocket called the Space Launch System (SLS). Orion has flown once, on an uncrewed test mission to Earth orbit in 2014, but the oft-delayed SLS has yet to get off the ground.

Related: Photos: NASA's Space Launch System for Deep Space Flights

The first flight of SLS, known as Artemis 1, will send an uncrewed Orion around the moon. That test mission is targeted for late 2020, Bowersox said. Artemis 2, scheduled for 2022, will launch four astronauts on a lunar flyby mission. Artemis 3 will deliver four astronauts to the Gateway in 2024; two of these pioneers will then make their way down to the lunar surface aboard a privately built lander.

Eddie Bernice Johnson, D-Texas, who chairs the House Science, Space and Technology Committee, voiced considerable skepticism that this plan will come together in time.

"It has been almost a decade since an American spacecraft sent astronauts into space at all. Yet the Administration's plan requires our astronauts to attempt a lunar landing on only the second crewed flight beyond low-Earth orbit after what by then will have been a 50-year hiatus, with no real plans for prior crewed preparatory flights in low-Earth orbit," Johnson wrote in her prepared statement for Wednesday's hearing , which was called "Developing Core Capabilities for Deep-Space Exploration: An Update on NASA's SLS, Orion and Exploration Ground Systems."

The paucity of crewed test flights is apparently an area of concern for Johnson, who noted that the 2024 lunar landing attempt will come as part of the first crewed mission to Gateway. And that surface mission might mark the first flights of the lander and the ascent vehicle that gets astronauts back up to the Gateway, she added.

"Rhetoric about American leadership in space and advancing the role of women in spaceflight is all well and good, but it is not a substitute for a well-planned, well-managed, well-funded, and well-executed exploration program," Johnson said in her written statement. "To date, Congress has not been given a credible basis for believing that the president’s Moon 2024 program satisfies any of those criteria. In short, if Congress is to support such a program, the Administration is going to have to do a lot more to provide such evidence."