GoKawiilJeff Thornburg helped turn a government research project into SpaceX’s most powerful rocket engine. Now, he’s trying to do the same thing at his startup Portal Space Systems, which is taking an idea set aside by NASA and turning into high-powered propulsion for the next generation of spacecraft.
Portal, founded in 2021, announced a $50 million Series A funding round Thursday that values the company at $250 million. The round was led by Geodesic Capital and Mach33, alongside Booz Allen Ventures, ARK Invest, AlleyCorp, and FUSE.
The company is developing a technology called solar thermal propulsion. Today’s standard satellite engines either burn chemical fuel, or convert the sun’s energy to electricity, using that to power efficient but low-powered thrusters. Portal’s engines would instead concentrate the heat of the sun, using that to heat propellant and move the spacecraft along at high speed.
The technology has been the subject of investigation in government research labs since the 1960s, most recently as a concept for sending a probe into interstellar space, but has yet to make it into orbit. Thornburg, along with co-founders Ian Vorbach and Prashaanth Ravindran, plans to change that in the next two years.
Thornburg began his career in the U.S. Air Force, where he worked on a program to develop an efficient, powerful next-generation kind of rocket engine that engineers call full-flow staged combustion. A decade later, he was wooed to SpaceX by Elon Musk to turn those concepts into the Raptor engine that now powers the company’s massive Starship.
After stints working at Stratolaunch and Amazon’s Project Kuiper, he turned to propulsion once again.
A new kind of rocket engine
Solar thermal power is, in Thornburg’s view, the next logical step in rocket tech. NASA had studied the technology extensively in the late nineties and concluded it provide better performance in many cases. It wasn’t developed further because there wasn’t enough demand for in-space mobility, according to a 2003 report commissioned by NASA.
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