Portal Space Systems raises $50M for solar thermal propulsion

Portal Space Systems, an aerospace startup founded in 2021, announced on Thursday that it has raised a $50 million Series A funding round. The round values the company at $250 million and will support the development of its solar thermal propulsion technology—a system that uses solar heat to heat propellant to move spacecraft.

The funding round was led by:

• Geodesic Capital
• Mach33

The round also included participation from:

• Booz Allen Ventures
• ARK Invest
• AlleyCorp
• FUSE

The startup is addressing a growing demand from the U.S. military for spacecraft that can fly quickly between orbits to “surveil or threaten rivals.” This represents a shift from the era when NASA researched solar thermal propulsion in the 1960s and released a report on it in 2003, but ultimately set the technology aside due to a lack of demand for in-space mobility. Portal’s founder, Jeff Thornburg, previously worked in the U.S. Air Force and later at SpaceX, where he helped develop the Raptor engine using full-flow staged combustion—a high-efficiency rocket engine cycle. Thornburg noted the urgency of the current geopolitical landscape, stating, “You know, China’s running circles around our spacecraft. We need equivalent capability.”

To date, Portal has received $45 million in strategic funding from the U.S. military alongside $67.5 million in private capital, driven by the technology’s potential application in “orbital warfare.” Thornburg, along with co-founders Ian Vorbach and Prashaanth Ravindran, plans to get the technology working in orbit in the next two years. The company’s flight electronics launched last week, and a prototype spacecraft is expected to launch in October. The first launch of its SuperNova spacecraft is expected in 2027. Thornburg argued that testing in space is more efficient than building infrastructure on Earth, asserting that he can mature the technology faster in orbit than by attempting to construct a $2 billion ground test facility that is nuclear safe.

Why it matters

Portal is reviving NASA-researched solar thermal propulsion to meet U.S. military demands for rapid orbital maneuvering, positioning itself to compete with rivals like China.