TransAstra CEO Joel Sercel with a prototype of a solar thermal engine.

By Tim Fernholz

TransAstra was founded in 2015 with the goal of mining asteroids. Yet harvesting resources out in the solar system, for all its appeal, is still far from feasible. Moving orbiting spacecraft around Earth? That is a service companies are willing to pay for, right now.

The trick of space business might be developing a lucrative path to a far-off vision. Elon Musk may want to retire on Mars and SpaceX may enable him to do so, but what’s significant about the firm is that it earns money providing space services in demand right now.

TransAstra founder and CEO Joel Sercel will, in theory, perform a similar sleight of hand: When its first spacecraft, dubbed Worker Bee, reaches orbit in 2023, it will show off a novel thruster technology called solar thermal propulsion, and earn money by precisely positioning satellites launched on larger rockets. And if that succeeds, it will launch a fleet of solar-powered spacecraft into orbit—and perhaps realize a larger vision of harvesting commodities from asteroids.

“The vision that Joel brings to the table is truly grandiose—just outside of the box, but in a truly feasible way,” explains Jason Derleth, who leads the NASA Innovative Advanced Concepts (NIAC) program, which has awarded millions of dollars of grants to TransAstra to develop frontier technologies.

Y Combinator, the early stage venture fund which has incubated start-ups like Airbnb, DoorDash, and Stripe, backed TransAstra as it raised a $4 million seed round in recent months to fund its transportation business, the company said last week.

Space Tug of war

The rise of commercial rockets and venture-backed satellites has created an opportunity for TransAstra to solve the equivalent of the “last mile” problem in space. To save money, satellite operators pack as many spacecraft as possible into orbital rockets, but a large rocket can only go to one destination in space. Satellites might need to be positioned in a variety of orbits and altitudes to do their work. Space tugs to cart satellites from their initial arrival point to a bespoke destination.

Analysts at Northern Sky Research estimate that companies are currently paying about $750 million to launch small satellites, a figure that could reach $1.5 billion annually by 2023. A dozen companies are at work on developing space tugs for this market; currently operational vehicles include the Photon kick stage operated by Rocket Lab, and Spaceflight’s Sherpa orbital transfer vehicle.

Another future option may be Vigoride, the space tug being developed by Momentus, a company founded by a Russian space entrepreneur, Mikhail Kokorich. Sercel spent 2019 as the chief technology officer of the company, with the idea of using Vigoride to demonstrate TransAstra’s mining technology, leaving the company that December.

This year, Momentus and its investors were charged with fraud by the SEC for lying about Kokorich’s immigration status and failed tests of the company’s thrusters. They settled by paying an $8 million penalty. Kokorich is in Switzerland, where he can avoid facing the fraud charges against him. He says he departed only because the US denied him a residency permit and forced him to divest from his company.

Momentus is the only publicly traded company focused on space tugs. The company’s market cap is less than $200 million, about a sixth of what the company’s investors expected when they decided to go public last year. It now forecasts that it won’t have a working space tug until next year.

“With traditional web companies like the ones that [Y Combinator] got started funding back in 2005, you have primarily market risk and only a little bit of technical risk. The real question you’re trying to figure out is, do people want what you’re making?” says Jared Friedman, a partner Y Combinator, which also invested in Momentus. “For hard tech companies, the bigger question is usually, can you make it?”

A steam kettle in space

Everything that happens in space depends on propulsion: What makes the SpaceX Falcon 9 rocket great is its Merlin engine; future rockets like Blue Origin’s New Glenn or SpaceX’s Starship will rise and fall on their own next generation thrusters.

Sercel says that what sets TransAstra apart is its solar thermal propulsion system, which sits in a sweet spot: More powerful than systems which convert solar power to electricity, and cheaper and more flexible than tugs using traditional chemical rockets.

The secret sauce for TransAstra almost seems too good to be true: A solar-powered engine capable of using almost any volatile chemical as fuel. The technology promises incredible efficiency—just focus sunlight on a fuel as universal as water, and point the resulting steam in the opposite direction you wish to go.

It was dreamed up in the 1950s by Krafft Ehricke, a German who had emerged from the Nazi rocket programs of World War II and emigrated to America in the US effort to scoop up scientists before the Soviet Union. Ehricke worked for NASA and then US defense contractors, dreaming up advanced space tech to carry humans into the cosmos.

NASA has considered solar thermal propulsion for its spacecraft, but ruled out pursuing the idea seriously at the turn of the century. At the time, engineers thought using such thrusters in space didn’t make sense with existing rockets, which were more expensive and carried less cargo. Larger and cheaper modern rockets have, arguably, changed this calculus.

Derleth, the NASA official, says Sercel’s team developed novel approaches to building this kind of engine, using inflatable, folded solar focusing lens and a special honeycomb ceramic to heat propellants. Sercel says a prototype thruster demonstrated enough thrust for the Worker Bee at the company’s Colorado test site in late August, and that two more prototypes in its southern California lab are proceeding through tests.

“It looks very promising, but it is early days and we have a lot more work to do,” Sercel says.