The founder helped build SpaceX’s most powerful rocket engine. He is currently building an “orbital fighter”

Jeff Thornburg helped turn a government research project into SpaceX’s most powerful rocket engine. Now he’s trying to do the same with his startup, Portal Space Systems. NASA is turning a shelved idea into a powerful propulsion force for the next generation of spacecraft.

The portal, founded in 2021, on Thursday announced a $50 million Series A funding round that values ​​the company at $250 million. The round was led by Geodesic Capital and Mach33, along with Booz Allen Ventures, ARK Invest, AlleyCorp, and FUSE.

The company is developing a technology called solar propulsion. Today’s standard satellite engines burn chemical fuels or convert solar energy into electricity, which is used to power efficient but low-power thrusters. The portal’s engines instead concentrate the sun’s heat and use it to heat the propellant and propel the spacecraft at high speed.

The technology has been the subject of research in government laboratories since the 1960s, and has recently been explored as a concept for sending probes into interstellar space, although it has yet to be launched into orbit. Thornburg, along with co-founders Ian Vorbach and Prashaanth Ravindran, plan to change that over the next two years.

Mr. Thornburgh began his career in the U.S. Air Force, where he worked on a program to develop an efficient and powerful next-generation rocket engine that engineers call full-flow staged combustion. Ten years later, he was lured to SpaceX by Elon Musk and turned those concepts into the Raptor engine that now powers the company’s massive Starship.

After working at Stratolaunch and Amazon’s Project Kuiper, he switched back to propulsion.

A new kind of rocket engine

In Thornburgh’s view, solar power is the next logical step in rocket technology. NASA studied this technology extensively in the late ’90s and concluded that it offered better performance in many cases. According to a 2003 report commissioned by NASA, there was not enough demand for in-space mobility, so it was not developed further.

At the time, flying satellites and space probes was much rarer, so it was easier to use more powerful rockets than to invest in in-space propulsion. Now, with thousands of new satellites flying each year and the U.S. military requiring spacecraft that can quickly fly between orbits to monitor or intimidate rivals, that calculus has been upended.

“Moving slowly in orbit is no longer acceptable,” Thornburg told TechCrunch. “As you know, China is circling our spaceships. We need comparable capabilities.”

Portal has already received $45 million in strategic funding from the U.S. military, in addition to $67.5 million in private capital, for the potential use of its technology in orbital warfare, said Travis Bales, managing director at Booz Allen Ventures.

And in a future where millions of satellites may provide communications and computing services in orbit around the Earth, satellite operators will need an inexpensive way to steer spacecraft out of each other’s way, said Aaron Barnett, CEO of aerospace-focused venture fund Mach33. Barnett sees Portal becoming a “space mobility prime” that provides propulsion to a variety of users.

path to orbit

To get there, the company’s technology needs to work in orbit. Its flight electronics were launched on a shakedown cruise around Earth last week, and another prototype spacecraft is scheduled for launch in October. The company plans to demonstrate a working prototype of the engine for the launch of its first supernova spacecraft (or “orbital fighter,” as Thornburg calls it) in 2027.

Portal benefits from recent advances in additive manufacturing and materials science, which led to the development of the company’s solar concentrator and nozzle combination hex thruster.

Rocket geeks see nuclear-powered rockets as the next step in enabling transportation across the solar system, but the regulatory and legal challenges of building such systems put them beyond the pay scale of startups.

But Portal’s engine also gives the company a head start on one version of a nuclear rocket: a nuclear thermal propulsion system, a system that replaces the sun’s heat with the heat of a nuclear reactor. When the U.S. government is ready to build it, Thornburgh’s team will have already demonstrated many of the moving parts in orbit.

“By trying to build a $2 billion nuclear-safe ground test facility, I think we’ll be able to mature this technology in orbit much faster than we’ve ever been able to before,” Thornburgh said.