SpaceX’s CTO of propulsion retired. Now he wants to go to Mars.

·5-min read

Tom Mueller is a self-described race car guy. Upon retiring from his role as CTO of Propulsion at SpaceX in November 2020, he "mostly wanted to go racing and ride dirt bikes and travel,” he said in a recent interview. Mueller, who is 61, was putting behind him a storied career: While at SpaceX, he led the development of the Merlin rocket engine, which powers the Falcon 9 rocket, and the Draco engines that power the Dragon spacecraft.

Retirement was the plan — but plans don't always work out as intended.

As soon as he retired, Mueller, who is widely considered one of the leading experts of propulsion alive today, started sketching up a small thruster. That thruster now has a name, "Rigel," after the blue supergiant in the constellation Orion. It's become a cornerstone of Mueller's new startup, Impulse Space, which he founded in September 2021. With the new venture, Mueller wants Impulse to be the go-to option for cost-effective, efficient in-space transportation.

“It was going to be just for fun and not too serious, but then some ex-SpaceX people started talking [to me] and wanted to help and all of the sudden it became real,” he said. “Now it’s full on.”

Rigel thruster Impulse Space
Rigel thruster Impulse Space

The Rigel thruster firing in the Mojave. image Credits: Impulse Space

To Mars

“Full on” might be an understatement. Impulse has raised a notable amount of money for such a young space startup, including a $20 million seed round led by Peter Thiel’s Founders Fund and a subsequent $10 million investment from VC firm Lux Capital. Given Mueller’s resume, he didn’t have to search very hard — or at all — for people willing to put their cash behind his ideas.

“Somebody asked me, ‘How long after you incorporated Impulse did it take for investors to want to give you money? And I said, ‘Well actually, I incorporated Impulse because I had investors tell me they wanted to fund me,” Mueller said.

Nor has Impulse had too much trouble finding talent. The startup has now grown to around 40 people, with many on the technical leadership team, such as Kevin Miller, VP of Propulsion, George Ketigian, VP of Integration, and Paul Seebacher, VP of Manufacturing, with prior experience at SpaceX. Impulse's COO, Barry Matsumori, also had a nearly four-year stint at SpaceX as the SVP of Sales and Business Development.

Impulse made the ambitious announcement earlier this month that it would be attempting a Mars mission with Relativity Space. The two companies, neither of which have yet to send their respective technologies to orbit, want to launch as soon as 2024. It was Relativity’s idea, Mueller said. He recounted how Zach Dunn, Relativity’s SVP of Engineering and Manufacturing and former SpaceX-er, approached Mueller about the mission. (Mueller and Dunn go way back, with Mueller hiring him for an internship at SpaceX.)

Impulse Space Mars Lander
Impulse Space Mars Lander

The Mars Lander. Image Credits: Impulse Space

“[Dunn] goes, ‘Are you in?’ I just thought it was the coolest thing. It was kind of scary — super scary, super hard, but I think we’re the right guys to do it. I actually feel better if I’m kind of scared.”

The agreement between Impulse and Relativity is through 2029. If they don’t make the 2024 launch date, they’ll have another opportunity when the stars (literally) next align, in 2026. Relativity will be providing the launch vehicle, its heavy-lift Terran R rocket, while Impulse will be building a Mars cruise vehicle spacecraft, entry capsule and lander.

If all goes to plan, the Mars mission will not be Impulse’s first mission. The company wants to fly an orbital transport vehicle late next year and is at work in the meantime running tests on the Rigel engine, making and testing valves, the avionics suite and more. And while Mars will likely be the most challenging mission on Impulse’s docket, Mueller has shown he is not the type to be cowed by a challenge.

A noble goal

Much of Mueller’s vision for Impulse is premised on launch becoming extremely low cost, and as a result, there being a lot of payloads in space that need to be moved around. He likened fully reusable heavy-lift rockets like Starship, Terran R and Rocket Lab’s Neutron to the internet in the early ‘90s. “People don't know really what it's going to do or what it's all about or what the real killer apps are,” he said.

Terran R will have a 20,000-kilogram payload capacity and Neutron will be capable of sending 13,000-kilograms to orbit. If SpaceX can pull it off, each Starship launch will be able to carry a staggering 100-150 tons. The possibilities that could arise from such a paradigm-shift in launch are hard to even conceive.

“I think that we're going be surprised how much is going to change in space to be able to put so much cargo up at so low cost,” Mueller added.

Relativity CEO Tim Ellis and SpaceX CEO Elon Musk have each separately talked about a vision for the future of humanity as one that is multiplanetary — in numerous public statements, Musk has summed up his mission as one to “extend the light of consciousness” in the cosmos — and Mueller is clearly on board to go to the Red Planet. But he said he’s also motivated by things slightly closer to home.

He pointed to the moon and the potential for a lunar and cis-lunar economy to help offload the resources of Earth. There are many valuable elements present on and below the Moon’s surface, as well as water and ice. Myriad startups, as well as the world’s major space agencies, have started eyeing up ways to exploit those resources. Mueller said he wanted to help build a future where heavy industry and power generation, two sectors that are notable for their carbon emissions, can move into space.

“That's like my noble goal,” he said. “It may not happen in my lifetime, but I think helping establish a low-cost reliable transportation network in space can help get it started.”

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