Astronaut candidate Robb Kulin is the first NASA astronaut in training to leave the Associated Press in the midst of this trial in 50 years  According to the AP report, Kulin recently decided to end his training at the Johnson Space Center in Houston with an effective termination date on Friday. NASA spokesman Brandi Dean described Kulin's departure to the news agency for personal reasons that could not be disclosed for privacy reasons. A similar departure of an astronaut from the training program of NASA had not existed since 1968.
A native of Anchorage, Alaska, Kulin holds a master's degree in materials science and a doctorate in engineering. Previously, he served as the Senior Space Safety Manager SpaceX before being selected from a pool of more than 18,300 applicants for one of the 12 members of the 2017 NASA class. At SpaceX, he worked on the Falcon 9 rocket to finally transport astronauts on the International Space Station on the company's still-developing Crew Dragon capsule. According to the AP, Kulin's career also included routes as a commercial fisherman and ice driller. (He's also reportedly a fan of Kerbal Space Program a space simulation game.)
Space.com noted that the astronaut training program is incredibly intense and requires the student divers to be certified for everything and The Russian language on robotics and flight systems:
Astronaut candidates must complete military water survival and become SCUBA-qualified to prepare them for their EVA training
… Astronaut candidates or "Ascans," are required to operate the International Space Station -Systems training, EVA and robotics skills training, Russian proficiency and flight flying readiness training to complete before space flight orders qualify.
According to Ars Technica, Space historian and CollectSpace editor Robert Pearlman said that the astronaut who left the program in 1968, the chemist John Llewellyn, decided he did not advance fast enough in his training o fly jet planes. However, there is no evidence that Kulin's departure has anything to do with a failure to qualify. The astronauts that run the program usually wait years for their first flight orders, and some do not land at all.
US Today, NASA does not expect to replace Kulin with another candidate. The 11 other members of the class of 2017 are still in training and 39 active astronauts on NASA's list remain eligible for missions.