The sudden ouster of Bill Gerstenmaier as the head of NASA’s human spaceflight program caught the space community by surprise. Hours earlier he had testified to a House committee about the future of activities in low Earth orbit (LEO) with no indication that anything was amiss. His deputy, former astronaut Ken Bowersox, will succeed him on an acting basis, but there is much scratching of heads as to what this means for NASA’s plans to get back to the Moon and on to Mars.

NASA Administrator Jim Bridenstine made the announcement about 8:30 pm ET. In a memo to employees, he said he was making the change in order to meet the Trump Administration’s goal of returning astronauts to the lunar surface by 2024 — the Artemis program. Also dismissed was Bill Hill, Assistant Deputy Associate Administrator for Exploration Systems Development. He has been in charge of development of NASA’s big new rocket, the Space Launch System (SLS), and Orion crew spacecraft. Tom Whitmeyer will replace Hill in an acting capacity.

The changes are effective immediately. Gerstenmaier has been reassigned as a special advisor to NASA Deputy Administrator Jim Morhard. Hill has been detailed as a special advisor to Associate Administrator Steve Jurczyk.

Gerstenmaier is a very highly respected 42-year NASA veteran. Since joining NASA in 1977, he has spent most of his career in the human spaceflight side of the agency working first on the space shuttle and space station programs. After the Cold War ended and the U.S.-Russian relationship thawed, he headed operations for the Shuttle/Mir program where U.S. astronauts visited Russia’s space station Mir and Russian cosmonauts flew on the U.S. shuttle. He became manager of Space Shuttle Program Integration, deputy manager and then manager of the International Space Station (ISS) program, and in 2005 became Associate Administrator for the Space Operations Mission Directorate at NASA Headquarters. When it merged with the Exploration Systems Mission Directorate in 2011, he took over as Associate Administrator of the new Human Exploration and Operations Mission Directorate (HEOMD).

Over the intervening years, he has crafted and defended a plan that he believed is affordable and able to weather changes in political winds to avoid the start and stop, start and stop cycles that have plagued NASA efforts to develop new rockets and crew spacecraft for decades. Moon? Mars? His architecture accommodates either or both. At its center is the Gateway, a small space station in lunar orbit that can serve as a transfer point down to the Moon or out to Mars. Lunar landers or a Deep Space Transport would be docked there to take crews to the desired destination.

NASA has not said what prompted the sudden dismissal of such an admired figure just hours after he testified to the House Science, Space, and Technology Committee about the ISS and NASA’s plans to commercialize LEO. Gerstenmaier and his team just rolled out a 5-point plan of how to do that last month. Granted, the plan did not get rave reviews at today’s hearing, with Democrats and Republicans questioning whether it is realistic, but Gerstenmaier stuck to the party line that NASA’s goal is to be one of many customers of commercial space stations in the future, not to build another one at government expense. Nothing obvious happened at the hearing that might have prompted his dismissal.

On the other hand, rumors have been swirling for quite some time that the White House is no fan of the Gateway. Gerstenmaier, and Bridenstine, see it as essential to a sustainable lunar exploration program. Bridenstine characterizes it as a reusable version of the Apollo Command and Service Module.

Others see it as a waste of time and money. There is a segment of the space community that wants to go directly to the surface, like Apollo, without the need to stop at a Gateway. Former NASA Administrator Mike Griffin called it a “stupid architecture” last year. A vocal contingent also wants to use commercial rockets instead of SLS to get to the Moon. SLS has solid support in Congress, but repeated cost overruns and schedule delays have eroded its standing elsewhere.

Bill Hill’s removal might have been tied to that. SLS prime contractor Boeing informed NASA earlier this year of yet another delay in the program. Instead of accepting the news, the White House decided to accelerate the return to the Moon. Artemis is the result. When Pence announced it, he issued warnings that if “contractors” could not improve their performance, others would be found, and if NASA could not get astronauts back on the Moon by 2024, NASA would have to change, not the goal.

NASA and Boeing have been trying to speed up SLS development since then. One issue is whether to proceed with a “Green Run” test where all four SLS engines are integrated into the core stage and fired for 8 minutes or skip it and rely on a much shorter test that would take place on the launch pad. Gerstenmaier told the NASA Advisory Council in May that his internal recommendation was to proceed with the test, but a decision had not been made. He expected one by the end of June, but there has been no announcement. Whether that debate played any role in today’s developments is unclear.

This is all speculation. More insight may be gained in coming days. All that is clear now is that just as the nation is about to celebrate the 50th anniversary of the Apollo 11 landing on the Moon, leadership of Apollo’s successor, Artemis, is in disarray.