As Blue Origin nears the critical point of delivering flight-ready BE-4 rocket engines to United Launch Alliance, the engineer in charge of the company’s rocket engine program has decided to leave.

Blue Origin CEO Bob Smith recently informed employees of the departure of John Vilja, the senior vice president of Blue Engines. In Smith’s email to employees, obtained by Ars, Vilja is said to be leaving Blue to pursue his “many” interests and hobbies outside of work.

“During his time at Blue, John led the team to support eight New Shepard missions powered by BE-3PM engines, countless hot fire tests, and made progress on multiple engines development programs,” Smith wrote. “He also built a world-class Engines team, recruiting some of the best talent in the business.”