In a first in five decades, a NASA astronaut candidate has resigned from training. According to the US space agency, Robb Kulin resigned from NASA effective August 31, a year after he was selected for the training.

According to an AFP report, NASA spokesperson Brandi Dean said Kulin cited personal reasons for leaving the agency. She did not provide further details.

In June 2017, Robb Kulin was selected to join NASA’s 2017 Astronaut Candidate Class. He reported to duty in August 2017 to begin two years’ training as an astronaut candidate.

At the time of his selection, according to his profile on the NASA website, Kulin was senior manager for flight reliability at SpaceX, leading the Launch Chief Engineering group in Hawthorne, California, where he had worked since 2011.

Kulin, who is from Alaska, has a Master’s degree in Materials Science and a Doctorate in Engineering from the University of California, San Diego, and was . previously an ice driller in Antarctica on the West Antarctic Ice Sheet and Taylor Glaciers. He was also a commercial fisherman in Chignik, Alaska.

The Fulbright Fellow was also a private pilot.

According to a USA Today report, NASA officials said Kulin won’t be replaced with a new astronaut candidate.

The NASA job he quit is not an easy one to get. According to reports, only 12 spots open each year and some 18,000 people routinely sent in their applications.