The return of NASA to US-based crew launches would kick off in less than desirable conditions: the agency announced that its associate human exploration director, Doug Loverro, quit his post on May 18 - nine days before the the first space mission of Crew Dragon with humans onboard. 

Loverro also left less than a half year after assuming the job. NASA did not disclose what made the administrator resign, but reports from SpaceNews said that there was a disagreement between Loverro and another administrator, Jim Bridenstine, about the nature of the space program.

Ars Technica learned it could be due to the bidding process for the lunar spacecraft that saw SpaceX, Blue Origin, and Dynetics bag contracts.

As head of the space agency's Human Exploration and Operations Mission Directorate, Loverro was expected to chair NASA's flight readiness evaluation Thursday, an important meeting to double-check systems and readiness and clear astronauts Douglas Hurley and Robert Behnken for launch on May 27 onboard the SpaceX space vehicle.

It will be the first launch of an orbital manned mission from American soil since NASA retired its space shuttle program in 2011.

For almost nine years, NASA has had to rely on the Russians to get its astronauts to the international space station. If all goes according to plan, the Crew Dragon mission will end that era next week.

In an email that Loverro sent to NASA staff, he disclosed that he was resigning because of a mistake he committed during his tenure, but he did not explain in detail the nature of the error.

"Now, over the balance of time, it's clear I made a mistake in that choice for which I alone must bear the consequences," Space News quoted the email as saying, and as per a story by Alan Boyle of GeekWire.

The reasons why Loverro left NASA are not clear, but they must be very compelling for him to depart at this critical moment when a program he managed enters its final phase.

Loverro was chosen to lead HEO in October, after the reassignment of Bill Gerstenmaier, who led the directorate for many years and reportedly quit after clashing with NASA Administrator Jim Bridenstine. Ken Bowersox, a NASA pioneer who served as acting administrator between the tenure of the two, will take over the role.

Meanwhile, the Trump administration has directed NASA to attain its goal of an accelerated push to send astronauts back to the moon in its Artemis program by end of 2024, four years earlier than previously planned.