According to Re/code, co-founder and chief technology officer of Hyperloop One, Brogan BamBrogan, has stepped down from his position at the company. The startup, which is angling to develop a super-fast enclosed transit system, promoted former Vice President of Engineering Josh Giegel to president of engineering and has given him a seat on the company’s board.

BamBrogan was a former SpaceX employee who temporarily served as Hyperloop One’s CEO until 2015. He joined the company after Shervin Pishevar, the other cofounder, had a conversation with Elon Musk, CEO of Tesla and SpaceX. While credited with coming up with a detailed white paper describing how a Hyperloop would work, Musk has declined to throw resources at building a Hyperloop himself, citing his many standing obligations.

Hyperloop One (formerly Hyperloop Technologies) is currently competing with Hyperloop Transportation Technologies (HTT) to see who can bring the 700mph magnetically driven rail system to fruition first. Notably, Hyperloop One is structured as a traditional startup, recently raising $80 million from investors including France’s national railway system, SNCF. HTT, on the other hand, depends largely on volunteer time from engineers who are also veterans of NASA, Boeing, Tesla, and SpaceX.

Per Re/code, “sources say there has been internal tension brewing at the company among the executives and that it was the cause of many of the abruptly made executive changes.” Other sudden departures include Afshin Pishevar, the chief legal officer for Hyperloop One and the brother of Shervin, as well as assistant general counsel David Pendergast.

The move is surprising because Hyperloop One seemed to have been doing well in recent months. It held a successful if underwhelming test of its propulsion system in May, secured healthy Series B funding, and most recently signed a deal with the Russian government and a Russian firm to build a Hyperloop in Moscow.