• Jim Cantrell worked at SpaceX during its earliest days in 2001 and 2002.
  • He was impressed by Elon Musk's vision but he would yell and once called Cantrell to work at 3 a.m.
  • Cantrell gives Twitter employees his advice on their new boss.

This as-told-to essay is based on a transcribed conversation with Jim Cantrell about his time working with Elon Musk as one of the founding employees at SpaceX. It's been edited for length and clarity.

When Elon first called me in 2001 I didn't know who he was — I'd never heard of PayPal. At the time, I was working as part of the space engineering team at Utah State University.

He explained over the phone that he was an internet billionaire and he wanted to prove that humans could be an interplanetary species.

Elon wanted to buy Russian rockets because they were cheaper than US rockets and had been told I was the guy to ask because I'd worked with the Russians.

We, with future NASA Administrator Mike Griffin, traveled to Moscow and were laughed out of there

Elon was in his late 20s, poorly dressed, and quite awkward. He was very bright and very determined, but even people in the US thought he was just a rich kid who wanted to dabble in space.

We were on the plane back and Elon turned to us and said, "I think we can build this rocket ourselves."

We were incredulous, but he showed us a spreadsheet that he'd been working on with Tom Mueller and Chris Thompson — engineers who were also part of the SpaceX cofounding team. They were the initial plans for the Falcon 1, the first vehicle SpaceX built, and I was impressed. 

I was tired of dealing with the inefficiency of the government. The plans Elon showed me were exciting.

I planned to see where it took me for a year or so. I was SpaceX's vice president of business development from December 2001 until I left in September 2002. Elon and I conflicted too much. He yelled at me a couple of times, and I would have had to change who I was to keep working there.

Working with Elon was like working with two different people: the good Elon and the bad Elon, and you never knew which you were going to get

The good Elon is very funny and charming. He brought you along with his big ideas, and you got to be a part of it.

The bad Elon would yell at you, and he would be frustrated. Nobody was good enough for him; nothing was good enough for him.

One time, he called me up at 3 a.m. demanding to know where I was because he was in the office. I told him "I went to bed three hours ago — I need more sleep than that." He wanted me to get down there because there was work to be done.

Elon wouldn't expect you to do anything he wouldn't do, but the lengths he's willing to go is unusual for most people. I suspect the same thing will happen at Twitter — from sheer force of willpower I think he will enhance the productivity there.

Another feature of working with Elon was that he always had a vision. With SpaceX it was to have people on Mars. He expected you to be 100% aligned with that objective. It was always clear in his mind, but he didn't always make it clear to his employees. There was a lot of guesswork.

I remember when we were building tanks for the rocket and we got in a fight. I had given him an estimate for the tanks, with the understanding we'd be building them ourselves, and he thought it was way too expensive. He yelled at me and was really upset.

He made me go out into Salt Lake City and look at truck tanks on the freeway and to a local steelworks factory to research these tanks and see if we could outsource them. It wasn't that he didn't trust my judgment; he just knew there was another way to approach the problem.

I learned a lot, but I felt disrespected. I didn't need to be paid to be shouted at, so I walked away.

There are people at Twitter who are going to need to decide whether they are 100% aligned with Musk's mission for it.

If there are employees not aligned with that vision, he will chew them out and he will do it in a vicious way, which is his right as owner. If you are aligned with his vision and immune to a very strong boss who's very demanding of your time and your thoughts, then it's going to be a very fun ride.

It depends on what people want in life — not everybody sees their career as the most important thing.

It's exciting being part of Elon Musk's vision. He would make speeches all the time during meetings about how important our work was at SpaceX, and I see him doing that at Twitter in pictures of him around the coffee bar.

Those speeches are helpful to keep you going. That's the good Elon. The bad Elon fired all the executives. He can be vicious — he's very capable of that.