NASA issued a short news release on Thursday evening stating that Jeanette Epps will not be a part of the International Space Station crew set to launch in June. (That flight would launch from Kazakhstan aboard a Soyuz rocket.) The release gave no reason why Epps was pulled from the flight.

In a response to a request for more information, Johnson Space Center spokeswoman Brandi Dean told Ars, "A number of factors are considered when making flight assignments. However, these decisions are personnel matters for which NASA doesn’t provide information."

According to NASA, Epps had returned to the active Astronaut Corps at the space center to assume duties in the astronaut office. She will be considered for assignment to future missions. Had she flown this year, Epps would have become the first African-American astronaut to live as a crew member aboard the International Space Station. Only three other African American women have flown into space. Epps' assignment in January 2017 garnered a fair amount of favorable publicity for the space agency.

Epps was a member of NASA's 20th class of astronauts, a group of nine known as the "Chumps" who were selected in June 2009. Seven of the nine astronauts from that class have already flown into space. Epps will be replaced by the other rookie from the 2009 class, Serena Auñón-Chancellor, who was serving as Epps' backup for this mission.

Crew members have been pulled from their flights much later than this. In 1970, Ken Mattingly was pulled from his assignment as command module pilot of the Apollo 13 just a week before launch. (Gary Sinise played him in the 1995 film.) That was because the primary crew was exposed to rubella, and Mattingly was not immune from the disease. NASA does not usually say why crews are reassigned unless there is a medical reason. In that case, NASA will sometimes provide limited information.