LAS CRUCES, N.M. — While NASA continues to wait to set a new official date for the first launch of its Space Launch System, an agency official said Oct. 10 that the launch could slip as late as the middle of 2021.

NASA’s formal estimate of the first launch of SLS, a mission called Artemis 1, remains late 2020. That date, though, assumes that everything will go exactly as planned for the remainder of the vehicle’s development and testing.

“The schedule that we’re managing to is very, very aggressive,” said Ken Bowersox, acting associate administrator for human exploration and operations at NASA, during a presentation at the International Symposium for Personal and Commercial Spaceflight (ISPCS) here.

That schedule calls for finishing the core stage of the vehicle at the end of this year and shipping it to the Stennis Space Center in Mississippi for a static-fire test known as the Green Run. “In the best case, it’s going to be five or six months” of testing there, he said.

He added, though, that there are “risks” to that timeline due to both technical issues, such as the amount of time needed to refurbish the stage after the test, as well as weather that can delay work on the outdoors test stand.

After the Green Run, the stage would be shipped to the Kennedy Space Center for integration with its two solid rocket boosters, upper stage and the Orion spacecraft that will perform an uncrewed test flight in cislunar space.

“We have a chance to actually have a rocket on the pad and launch by the end of next year,” he said. “But when you start throwing all those different uncertainties, it’s more likely that we will move out into 2021.”

Earlier in his speech, he suggested that the Artemis 1 launch could slip well into 2021. “Some time late next year, middle of the year after,” he said, “the first uncrewed Orion will be launched out around the moon.”

Bowersox’s comments are the strongest signal yet that a 2020 launch of the SLS appears unlikely. Slips in the schedule in March prompted NASA Administrator Jim Bridenstine to propose flying what was then known as Exploration Mission 1 on an alternative vehicle to the SLS, a proposal strongly opposed by congressional supporters of the rocket and which the agency ultimately decided not to pursue.

NASA also considered shortening or doing away entirely with the Green Run as a means of saving several months of schedule. That move was opposed by many agency advisors, including the Aerospace Safety Advisory Panel, and Bridenstine announced in July that the agency would go ahead with the Green Run test.

A formal decision on a new launch date, Bowersox said, won’t come until the agency hires a new associate administrator for human exploration and operations. Bowersox, a deputy associate administrator, has held the position in an acting capacity since Bridenstine reassigned longtime associate administrator Bill Gerstenmaier three months ago.

“When we name a new [associate administrator], we’re going to give that person a chance to look at all of the schedule analyses that have been done, and let them rebaseline the date and cost information,” he said.

NASA, though, has not appeared to be in a rush to select a permanent successor to Gerstenmaier. Bowersox noted that, when he testified before a House committee Sept. 18, he estimated that person would be selected “by the end of the year,” a schedule he said he was then told by agency leadership was too long. “Now what I say is somewhere between a few weeks and a few months.”

Bridenstine, speaking Oct. 10 at SpaceX’s headquarters in Hawthorne, California, after a meeting with Elon Musk, praised Bowersox for his interim leadership. “He’s doing great work,” Bridenstine said, arguing that it would not, at least, delay any commercial crew test flights. “As of right now, I’m very confident we can continue moving forward and not have any delays because of the opening in that position.”

Bridenstine hinted that the search for a new associate administrator may soon end. “We will come to a point where we settle on a name, but we’re not there yet,” he said. “That announcement is not months away, it’s weeks away.”

Bowersox said he was interested in taking the associate administrator position on a permanent basis. “If I wasn’t interested in the job, I wouldn’t still be here as the acting” associate administrator, he said. “I’d be happy to serve in the position.”