Most satellites, once deployed, stay where they are put. A communications bird in geostationary orbit sits there for 15 years. A reconnaissance satellite in LEO flies the same ground track until its propellant runs out and it deorbits. Moving between orbits (from LEO to GEO, from GEO to cislunar space) requires either so much fuel that the maneuver consumes most of the spacecraft's mass, or so much time that electric propulsion takes months to change position.
Portal Space Systems just raised $50 million to build spacecraft that can actually maneuver.
The Series A round, led by Geodesic Capital and Mach33 with participation from Booz Allen Ventures, Ark Invest, AlleyCorp, and FUSE, values the Bothell, Washington-based company at $250 million. Total private funding now stands at $67.5 million, on top of $45 million in contracts from the U.S. Space Force through the SpaceWERX program.
The company's core technology is a solar thermal propulsion system that uses focused sunlight to heat an ammonia-based propellant to extreme temperatures before expelling it through a nozzle. The approach delivers a specific impulse of roughly 800–1,000 seconds — about double what chemical propulsion achieves and comparable to nuclear thermal propulsion, without the reactor. Portal's founder and CEO Jeff Thornburg, who previously served as senior director of propulsion at SpaceX (architect of the Raptor engine) and head of mechanical engineering and manufacturing for Amazon's Project Kuiper, calls it a matter of simplicity: solar thermal avoids the regulatory and cost hurdles of nuclear while still enabling orbital transit times measured in hours or days rather than weeks.
Portal is developing two spacecraft platforms around this engine. Starburst is an ESPA-class maneuvering bus designed for rapid operations within a single orbital regime — LEO, MEO, or GEO — delivering roughly 1 km/s of delta-v. Starburst-1 is scheduled to launch this fall on SpaceX's Transporter-18 rideshare mission for a one-year demonstration of rendezvous and proximity operations. Supernova is the larger, transorbital vehicle: it can move from LEO to GEO or from GEO to cislunar space in days rather than months, carrying customer payloads on its front end. The first Supernova is targeted for 2027.
The Series A capital will finance a 52,000-square-foot production facility in Bothell, set to open in June 2026. At full capacity, the factory will produce 12 Supernova and 16 Starburst vehicles per year — a production rate that signals Portal's intent to move from demonstration missions to sustained manufacturing. The company has grown to roughly 40 employees and expects to double that by the end of 2026.
Portal's thesis, that maneuverability is becoming a strategic requirement for both military and commercial operators, aligns with a broader shift in the space industry. The Space Force's "dynamic space operations" doctrine explicitly requires spacecraft that can reposition without sacrificing mission life. Commercial operators flying large LEO constellations need collision avoidance that doesn't burn through their station-keeping budget. And the nascent in-orbit servicing market depends on vehicles that can reach customers in different orbits, not just the one they launched into. Portal is betting that solar thermal propulsion gives it a cost and performance advantage over both chemical and electric alternatives for this emerging market, and that a factory turning out 28 spacecraft a year will be ready when the demand arrives.
