This founder helped build SpaceX’s most powerful rocket engine. Now he’s building a ‘fighter jet for orbit’

Jeff Thornburg, a prominent figure behind SpaceX's most powerful rocket engine, is embarking on an ambitious journey with his startup, Portal Space Systems. The company is set to transform a concept previously sidelined by NASA into a groundbreaking propulsion system for future spacecraft. Founded in 2021, Portal recently announced a significant milestone: a $50 million Series A funding round that values the company at $250 million. This funding was spearheaded by Geodesic Capital and Mach33, along with contributions from Booz Allen Ventures, ARK Invest, AlleyCorp, and FUSE. Portal is venturing into solar thermal propulsion technology, which diverges from the conventional satellite engines that rely on chemical fuels or convert solar energy into electricity. Instead, Portal’s innovative engines aim to harness concentrated solar heat to heat propellant, propelling spacecraft at unprecedented speeds. Despite being a concept explored by government labs since the 1960s, this technology has yet to be utilized in space. Thornburg, alongside co-founders Ian Vorbach and Prashaanth Ravindran, is determined to make this dream a reality in the next two years. Thornburg’s expertise began in the U.S. Air Force, where he contributed to the development of advanced rocket engines. He later played a pivotal role at SpaceX, helping to create the Raptor engine that fuels the Starship. After gaining experience with other aerospace ventures, Thornburg returned to propulsion technology, believing solar thermal power is the logical next step in rocket development. NASA's previous studies in the 1990s indicated that this technology could yield superior performance. However, it was sidelined due to a lack of demand for in-space mobility, as a 2003 NASA report noted. With the surge in satellite launches and military needs for rapid orbit shifts, the situation has dramatically changed. “It’s no longer acceptable to move slowly in orbit,” Thornburg stated in an interview with TechCrunch. He emphasized the urgency for the U.S. to match the swift capabilities of other nations in space. Portal has already secured $45 million in strategic funding from the U.S. military, in addition to $67.5 million in private investments, thanks to the potential applications of its technology in orbital warfare. The demand for agile spacecraft is growing, with thousands of new satellites entering orbit each year, prompting the need for cost-effective maneuvering solutions. Aaron Burnett, CEO of Mach33, envisions Portal as a leader in space mobility, providing propulsion systems for a diverse range of users. To realize this vision, the company must demonstrate its technology in space. Recently, its flight electronics were launched for testing, and another prototype spacecraft is slated for an October launch. Portal is set to unveil its first SuperNova spacecraft, dubbed a “fighter jet for orbit” by Thornburg, with an expected launch in 2027. Recent advancements in additive manufacturing and materials science have facilitated the development of the company’s innovative solar concentrator and nozzle, known as the Hex thruster. While some experts believe that nuclear-powered rockets represent the future of solar system travel, Thornburg acknowledges the regulatory hurdles involved in such projects. However, Portal’s engine positions the company to contribute to nuclear thermal propulsion systems, enabling it to replace solar heat with reactor heat when the government is ready to pursue that path. “Testing in orbit will accelerate technological maturity much faster than building a $2 billion ground facility for nuclear safety,” Thornburg asserted. The future of space travel may hinge on the success of innovations like Portal’s solar thermal propulsion, as it seeks to redefine how we navigate the cosmos.