From left to right: Serena Auñón-Chancellor; Jeanette Epps; Anne McClain. Photos: NASA

The astronaut who was scheduled to lift off for space in May, and who would have made history, was reassigned without specific plans for future missions, NASA announced Friday.

Jeanette Epps, now 47, who was announced as part of the Expedition 56/57 crew last year, would have been the first African American astronaut to join the crew of the International Space Station.

However, she is now returning to NASA’s Johnson Space Center in Houston, and will be considered for assignment in future missions, according to the space agency. A cause was not given – though an agency spokeswoman told Newsweek that it was a personnel matter that they would not comment on.

Epps will be replaced by Serena Auñón-Chancellor, an astronaut who was anticipated to blast off in November 2018 as part of Expedition 58/59. In turn, Auñón-Chancellor’s seat on the ISS will be taken by Anne McClain, a member of the 2013 astronaut class.

Auñón-Chancellor has a doctorate in medicine, and also has a degree in electrical engineering. She became a flight surgeon in 2006, before joining the astronauts in 2009.

McClain has master’s degrees in aerospace engineering, as well as international relations. She flew more than 800 combat hours in Operation Iraqi Freedom, and graduated from the U.S. Naval Test Pilot School in June 2013.

Epps earned her doctorate in aerospace engineering from the University of Maryland. She worked in the Ford Motor Company research laboratory for two years, before serving seven years as a technical intelligence officer for the Central Intelligence Agency.

She was selected as one of 14 members of the 20th NASA astronaut class in 2009. Subsequent training included the Russian language, spacewalking, robotics and T-38 jet training.

Epps is not the first black astronaut, however. Mae C. Jemison was the first black woman to reach space when she spent eight days orbiting the Earth aboard the space shuttle Endeavor as part of a seven-member crew in September 1992.