CNBC reports that SpaceX’s leadership team has seen two of its vice-presidents leave the company.

With the changes come Elon Musk’sWith its Falcon 9 rockets and Falcon Heavy, the space firm is America’s leading rocket maker. It is investing in its Starship rocket development.

Multiple people with knowledge of the matter told CNBC that SpaceX Vice President for Propulsion Will Heltsley, who has been employed at the company since 2009, has resigned. According to those people, Heltsley was removed from Raptor engine design because of a lack in progress. SpaceX’s Starship rockets and Super Heavy boosters are powered by the Raptor engines.

Heltsley’s departure shows the immense pressure that the engine is under, considering the critical role it plays for Starship’s success. They have successfully conducted numerous test firings with Raptor and flown the engine many times, continually improving it. Musk stated recently that the Raptor’s second-generation engine will “show significant improvement in all aspects.”

Musk said that a redesign of the design is needed for an engine capable of making life multi-planetary. Musk stated in a tweet that the engine won’t go by Raptor. Nov. 16.

SpaceX’s Jacob McKenzie is the current leader of Raptor engine design and production. McKenzie joined SpaceX in 2006, according to sources.

SpaceX Vice President of Mission and Launch Operations, Lee Rosen, has resigned, according to people. Ricky Lim was also leaving last week as senior director for mission operations. Rosen joined SpaceX in 2013, and Lim joined it in 2008.

CNBC reached out to SpaceX for comments on their leadership change.

After SpaceX’s purchase offer was closed on Friday, a few other employees who were long-term workers left. Sources familiar with the matter said that this timing may have been due to stock vesting plans. While SpaceX did not raise new capital in the secondary sale, the round was done at $560 a share – increasing the company’s valuation to $100.3 billion.

SpaceX is having a great year. SpaceX launched 25 Falcon 9 missions and 12 astronauts were sent to orbit by its Dragon capsules. It also increased its Starlink satellite internet service from about 140,000 to over 140,000 subscribers. Starship continues to progress.

Musk said last week SpaceX will “hopefully” launch its first orbital Starship flight in January or FebruaryThe next milestone in the development of the rocket is. This launch awaits regulatory approval from the FAA and technical readiness.