William Gerstenmaier may not have been not particularly well-known to the general public, but as the associate administrator for human spaceflight at NASA he carried considerable influence in the space community. So when he was effectively terminated from his position on July 10, it reverberated both throughout the domestic as well as the international spaceflight community.

NASA chief Jim Bridenstine, who moved Gerstenmaier aside because of ongoing delays with the Space Launch System rocket and a concern that the senior official was not moving ahead quickly enough with the Artemis Moon program, has said new leadership will be in place "soon."

This will be a critical hire for Bridenstine, as his new associate administrator for human spaceflight will have a number of important and difficult calls to make upon taking the job—and not just concerning the White House's efforts to return to the Moon by 2024. In particular, in the coming months, Gerstenmaier's replacement will be chairing meetings called "Flight Readiness Reviews" that will give a green light to the first crewed missions from US soil since 2011.

Losing Gerst may hurt

SpaceX has already flown an uncrewed demonstration mission of its Dragon spacecraft. Boeing is likely to follow suit this fall with its own Starliner capsule, possibly as early as September. Then each company will have a critical test of its spacecraft's abort system, and then a chance to work through any final technical issues. But once that's done, one or both of the vehicles could be ready to launch astronauts from Florida by early 2020.

"Here’s where losing Gerstenmaier is going to hurt," said Wayne Hale, former space shuttle program manager and an adviser to NASA. "Bill was recognized by everybody as being technically well grounded and very astute. He was known to listen carefully, and to make his judgments based on good technical reasons."

For example, in 2006 there were technical concerns about the Atlas V rocket to be used for the launch of the New Horizons spacecraft after a liquid oxygen tank had cracked during testing. At the time, the Atlas V had flown just a handful of missions, and Gerstenmaier had responsibility for the safety of launch vehicles used for NASA payloads.

In his book Chasing New Horizons, New Horizons' principal investigator Alan Stern described the tense 2006 meeting to give the mission's launch a go or no-go vote: "Gerstenmaier voted to launch, explaining calmly and carefully why he thought that the proof of the tank-burst issue had been studied and analyzed thoroughly and that the analysis had clearly exonerated any risk for the New Horizons launch. He said that launching was the rational choice."

Not everyone may have agreed with this choice, but NASA's new administrator at the time, Mike Griffin, did. He overruled the objections and gave a green light for launch. Because Gerstenmaier had credibility, no one went public to complain about the process or raise concerns prior to liftoff. The Atlas V rocket, of course, did its job, and the New Horizons mission has since successfully reached and explored Pluto.

A "contentious" meeting

There will almost certainly be some sort of controversy with the first commercial crew flights, given the overall stakes with humans on board and the more purely commercial nature of the contracts. Moreover, both SpaceX and Boeing have had accidents just before, during, or after hot-fire tests of the thrusters to be used during a launch abort emergency.

"Somebody is going to be unhappy," Hale said of the Flight Readiness Reviews for the first crewed flights of the new vehicles. "I guarantee it. If it’s not one thing it will be another. There will be a contentious meeting and somebody is going to have to say, 'Well, I heard the story and I think we ought to go ahead.'"

That somebody will almost certainly be the new associate administrator for human spaceflight. And depending on his or her experience, NASA managers and rank-and-file employees may decide they don't know the new person or don't think he or she has the technical capacity to make such a complex decision. As a result, they may go talk to newspapers or members of Congress to air their concerns.

"It’s potentially going to be ugly, and they wouldn’t have done that with Bill," Hale said. "If Bill were there and said 'I heard you, and I think the risk is acceptable,' the NASA workforce would have gone along. Now, they’ve lost that."