Jeanette Epps was about to become the first African American to live at the International Space Station.

But NASA announced in January it was replacing her with another astronaut. Epps said this week that she still doesn't know why.

Appearing at a conference, Epps said she didn't want to speculate that the decision was racist or sexist, an accusation many critics made after the announcement.

Jeanette Epps was preparing for a historic launch to the International Space Station in January when NASA suddenly pulled her off the mission without warning.

Epps is still waiting for an explanation, the Houston Chronicle reported.

In a January press release, NASA announced that Epps would not be part of the Expedition 56/57 crew as previously announced and that she would "return to NASA's Johnson Space Center in Houston to assume duties in the Astronaut Office and be considered for assignment to future missions."

Rachel Becker of The Verge noted that although other African Americans had been to the International Space Station, Epps would have been the first to live and work there on a long-term basis.

On June 6, the six-month mission launched without Epps. NASA sent Serena Auñón-Chancellor in her place, making Auñón-Chancellor the first Hispanic woman to live on the ISS.

Speaking about the issue for the first time at the Tech Open Air Festival this week, Epps told Space.com reporter Megan Gannon that she did not have any of the health of family issues that are typical reasons for crew changes. Epps said crew members have been taken off missions before, "but not in the same fashion that this was done, partly because I was so close to launch."

Epps believes the decision originated at NASA and not with their Russian flying partners, who she said were supportive.

"I don't know where the decision came from and how it was made, in detail or at what level," she said. "I seriously do not believe it was the Russians, partly because I had been through the training with them and I was able to develop good working relationships with everyone there."

Since NASA's announcement to remove Epps from the mission, the space program has received complaints of racism and sexism.

"There's no time to really be concerned about sexism and racism and things like that, because we have to perform," Epps told Gannon during the interview. "I can't speculate what people are thinking and doing unless I have a little bit more information."

Before becoming an astronaut in 2009, Epps, a native New Yorker, worked at Ford Motor Company and the CIA.