Douglas Loverro, NASA’s chief of human spaceflight operations, has unexpectedly resigned, just a few days before the long-waited resumption of American astronaut launches from U.S. soil, the agency announced Tuesday.

As director of NASA’s Human Exploration and Operations Mission Directorate, Loverro had been expected to chair NASA’s flight readiness review Thursday, a critical “all hands” meeting to double-check preparations and clear astronauts Robert Behnken and Douglas Hurley for launch May 27 aboard a SpaceX Crew Dragon spacecraft.

The astronauts are expected to fly to the Kennedy Space Center Wednesday to begin final preparations for launch.

Douglas Loverro, NASA’s former associate administrator for the Human Exploration and Operations Mission Directorate at agency headquarters, during a NASA “town hall” meeting last December.

NASA

The long-awaited mission to the International Space Station is a critical milestone on the road to ending NASA’s sole reliance on Russian Soyuz spacecraft for transportation to and from the lab complex and maintaining a large enough crew to carry out meaningful research.

NASA Administrator Jim Bridenstine hired Loverro last October after long-time spaceflight chief Bill Gerstenmeir was forced to step down in the midst of the agency’s accelerated push to send astronauts back to the moon in its Artemis program.

The Trump administration has directed NASA to accomplish that goal by the end of 2024, four years earlier than previously planned, a goal that strikes many as unrealistic. But NASA is forging ahead with contracts and detailed planning.

Loverro has played an active role in key NASA decision points over his short tenure, including a review of problems that prevented an unpiloted Boeing commercial crew capsule from carrying out a rendezvous and docking with the space station last December and recent contract awards for development of new moon landers for the Artemis program.

In a letter to HEO directorate employees posted by Spaceref, Loverro said he “truly looked forward to living the next four-plus years with you as we returned Americans to the surface of the moon and prepared for the long journey beyond. But it is not to be.”

“Throughout my long government career … I have always found it to be true that we are sometimes, as leaders, called on to take risks,” he wrote. “Our mission is certainly not easy, nor for the faint of heart, and risk-taking is part of the job description. The risks we take, whether technical, political, or personal, all have potential consequences if we judge them incorrectly.

“I took such a risk earlier in the year because I judged it necessary to fulfill our mission. Now, over the balance of time, it is clear that I made a mistake in that choice for which I alone must bear the consequences. And therefore, it is with a very, very heavy heart that I write to you today to let you know that I have resigned from NASA effective May 18th, 2020.”

He did not identify the nature of his “mistake” and NASA offered no additional insight in its own note to agency employees.

NASA to launch first manned mission to space in nearly a decade

“Loverro hit the ground running this year and has made significant progress in his time at NASA,” the agency said. “His leadership of HEO has moved us closer to accomplishing our goal of landing the first woman and the next man on the Moon in 2024. Loverro has dedicated more than four decades of his life in service to our country, and we thank him for his service and contributions to the agency.”

The statement said former shuttle commander Ken Bowersox, who served as a deputy to Gerstenmeir and Loverro, has taken over as acting associate administrator of the Human Exploration and Operations Mission Directorate. NASA said the agency had “full confidence” in the commercial crew team led by Program Manager Kathy Lueders.

“Next week will mark the beginning of a new era in human spaceflight with the launch of NASA astronauts Bob Behnken and Doug Hurley to the International Space Station,” NASA said in its message to agency workers. “We have full confidence in the work Kathy Lueders and her entire Commercial Crew team have done to bring us here.”