SpaceX's 7th hire describes what it's like to work with Elon Musk: 'He expects a lot, and that's a challenge'

• Hans Koenigsmann, SpaceX's seventh hire, spoke to Insider about working with Elon Musk.
• Koenigsmann said Musk "expects a lot" of his staff and provided a "unique perspective" on physics.

Elon Musk's seventh hire at SpaceX has said that the billionaire businessman expects a lot from his staff - and that could be a "challenge."

German aerospace engineer Hans Koenigsmann, a former vice president at SpaceX, retired from the company in early October after 19 years there, having in February announced his intention to leave.

During his time at SpaceX, Koenigsmann was in charge of several missions and launches. He worked for a few years on the company's satellite internet service, Starlink. He was also involved with the company's first all-civilian mission to space, Inspiration4.

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Koenigsmann was hired in 2002, the same year that SpaceX was founded. Musk went to Koenigsmann's house to do the interview because SpaceX didn't have an office - and in the company's early days, "we met at hotel conference rooms," Koenigsmann said.

In an interview with Insider, Koenigsmann described his departure from SpaceX as "bittersweet." He said he was sad to leave but also optimistic about starting a new chapter in his life after nearly 20 years at Musk's aerospace group.

There was always a lot of work to do at SpaceX, Koenigsmann said: he worked evenings and on weekends to catch up with his heavy workload. But he said he "never had a day where I went there and was thinking I don't want to do that work," adding that he was always motivated and happy.

Musk "didn't know a lot about rockets initially, but he learned a lot over time," Koenigsmann said. Musk picked knowledge up quickly, which was "amazing to watch," he added.

"I really enjoyed working with him and learning how he sees things," Koenigsmann said. "He sees things from a different perspective."

Musk provided a "unique perspective" on scenarios involving basic physics by asking what the limiting factor was, according to Koenigsmann.

An example of this was when Musk pushed his engineers to shorten the time it took to fuel SpaceX's rockets. Musk said SpaceX should aim to reduce the time from 30 minutes to eight minutes - the same time it takes to empty a rocket tank, according to Koenigsmann.

SpaceX uses propellant at very low temperatures to increase its density, allowing engineers to cram more into each rocket, Insider previously reported. Rockets need to be fueled quickly before launch so the propellant doesn't warm up.

As a result of Musk's direction, SpaceX's rockets are fueled "in a remarkably short time," Koenigsmann said.

Koenigsmann said that after he announced he was retiring, Musk wrote to him saying he could return to SpaceX to visit him and see Starbase, SpaceX's proposed city in Boca Chica, Texas.

Koenigsmann is now a board member of laser communication company Mynaric, which is headquartered in Munich, Germany.