Last year, NASA announced the addition of twelve new astronaut candidates into the rigorous training program that would one day lead to space. Historically, making it into the astronaut candidate class for a certain year represents the single biggest hurdle between a qualified candidate and actually making it into orbit, as the process is so competitive, few have ever made it into a class and then failed to follow it through to completion. With only 12 candidates chosen from a field of more than 18,300 candidates last year, those who make it tend to only be those with the “right stuff;” no one has voluntarily resigned from astronaut training in five decades.

That is, until now. Robb Kulin, one of last year’s 12 new astronaut candidates, announced on Monday that he would be resigning from astronaut training, citing personal reasons. Neither he nor NASA, have elaborated on what those reasons may be, as Kulin is forfeiting not only his chance to escape Earth’s gravitational clutches but could have been among the first generations of astronauts to fly aboard privately developed platforms fielded by the likes of SpaceX and Boeing. Flying aboard the SpaceX Crew Dragon capsule, in particular, was of import to Kulin in previous statements, as he was a former employee of the space fairing company and hoped to one day get to actually use components in space that he once helped to design.

However, instead Robb Kulin will depart from astronaut training on August 31st, and according to a statement from NASA PR director Brandi Dean, he will not be replaced by another candidate. Instead, the class of 2017 will carry on with only eleven official candidates.

“He will not be replaced in the astronaut candidate class,” Dean told Newsweek. “When selecting an astronaut candidate class, we estimate needs within the astronaut corps based on available information at the time, and account for the fact that we cannot fully predict attrition levels and other issues that might affect the number of astronauts available for assignment.”

Up until this week, Kulin seemed the perfect fit for the new era in space travel many believe humanity is now approaching. Aside from having a doctorate in engineering, Kulin has worked in some of the world’s least hospitable climates, doing some of the world’s most dangerous jobs. Aside from his engineering work at SpaceX, Kulin worked as an Antarctic ice driller on the West Antarctic Ice Sheet, as a commercial fisherman in the treacherous waters off the coast of Alaska, and has earned his pilot’s license.

At SpaceX, Kulin became the senior manager for flight reliability before being accepted by NASA for their astronaut training program. According to reports NEWSREP has not been able to verify with Kulin, who is currently not making statements to the media, Kulin was accepted into the astronaut program upon his third time applying, making his sudden departure all the more mysterious.