HOUSTON - NASA is making changes to its lineup of astronauts who will travel to the International Space Station this year.
Astronaut Jeanette Epps was scheduled to go to the ISS in June.
Epps would have been the first African-American astronaut to live on the ISS.
NASA's announcement of Epps joining the crew went viral in 2017.
While other African-American astronauts have spent time on the Space Station, Epps would have been the first to live and work on the craft for months at a time as a full crewmember.
Instead, she will take on duties at Johnson Space Center.
NASA said Epps will be considered for future assignments.
Astronaut Serena Auñón-Chancellor is taking her place on the Expedition 56/57 crew, which launches in June.
It is unclear why Epps was replaced on the mission.
A doctors explains reasons why an astronaut would be reassigned.
“Oh, I think a lot of reasons,” said Dr. Carolyn Sumners, the vice president of Astronomy at the Houston Museum of Natural Science.
Sumners has helped train astronauts for flight.
“They have to believe that your health is stable for that amount of time. They have to believe that your family is stable for that amount of time and mean that there's nothing that would mean that you just had to come home because you won't be able to," Sumners said.
She said during shorter missions, such as during the Space Shuttle days, a flight would last a maximum of a couple of weeks, but now a mission on the ISS could last months or even a year.
Sumners said a mission to Mars would last for years.
"What would cause an astronaut to be dropped would be a lot of things and this (is) gonna get harder and harder as we talk about trips to Mars. The longer the trip, the longer someone is going to be separated from family, from support structure, from their obligations on Earth," she said.
NASA's spokesperson, Brandi Dean, released the following statement:
“A number of factors are considered when making flight assignments; these decisions are personnel matters, for which NASA doesn’t provide information. Epps has returned to the active astronaut corps at JSC to assume duties in the astronaut office. She will be considered for assignment to future missions.”
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