5 minute read•Updated 2:06 PM EDT, Sat April 5, 2025
Portal Space Systems, a aerospace startup developing next-generation spacecraft propulsion, has raised $17.5 million in a seed funding round to support the development and upcoming launch of Supernova, its highly maneuverable spacecraft powered by solar thermal propulsion (STP).
The funding round was led by early-stage investor AlleyCorp, with participation from Mach33, FUSE, First In, TFX, Offline Ventures, Atypical, and several other strategic investors. The funding will carry Portal through the final stages of Supernova development and into a 2026 demonstration mission aimed at proving its capability to rapidly reposition between orbits; an increasingly critical demand in both commercial and national security space operations.
“This funding is a testament to the increasing recognition that maneuverability at will is the critical need in both defense and commercial space operations...With the support of our investors, we are moving from development to flight, bringing this capability to missions that need it most.” - Jeff Thornburg, CEO and Co-Founder of Portal
Supernova: A Revolutionary Solar Thermal Spacecraft
Portal’s flagship spacecraft, Supernova, is designed around a proprietary solar thermal propulsion system that utilizes concentrated sunlight to heat a storable propellant and generate thrust. The result is a system capable of achieving up to six kilometers per second of delta-V, with high thrust and the efficiency to make long-range, rapid orbital transfers.
Unlike traditional electric propulsion or nascent nuclear thermal propulsion systems, Portal’s STP offers a simpler, scalable alternative that leverages sunlight not reactors as an energy source. The implications are game-changing: Supernova could traverse from low Earth orbit (LEO) to medium Earth orbit (MEO) in minutes, or from LEO to geostationary orbit (GEO) in a matter of hours.
“It’s a high delta-V capable machine that really addresses both commercial and military mobility needs on orbit right now,” - Jeff Thornburg, CEO and Co-Founder of Portal
Though Portal refers to Supernova as a spacecraft bus, it operates far beyond that label. It serves as an agile orbital maneuvering vehicle, enabling deployment of hosted payloads into custom orbits, facilitating close-proximity operations, and offering repositioning services once considered logistically and economically impractical.
“I didn’t want to leave any money on the table, and there’s a lot of people that need delta-V, but not necessarily for the same thing,” - Jeff Thornburg, CEO and Co-Founder of Portal
Supernova Demo Mission in 2026
With its $17.5 million seed round now secured, Portal has outlined a clear roadmap to first flight.
Completed additive manufacturing of a full-scale STP heat exchanger/thruster
Expanded into an 8,000-square-foot HQ in Bothell, Washington, complete with propulsion testing infrastructure
Grew to a team of 25, bringing in key engineering and operations talent
Secured an additional $2 million in government funding (details undisclosed)
In the coming months, Portal plans to complete a Critical Design Review (CDR) and begin full-scale thruster testing. Integration of the first flight unit will commence in Q4 2025, ahead of a mid-2026 launch on a dedicated demonstration mission.
If successful, Portal will ramp up production, initially targeting one Supernova spacecraft per month, with plans to scale further to meet anticipated demand.
“I want us to be ready to start producing these things upon successful demonstration...I’m pretty confident based on the customer interest that once the demonstration flight occurs, we’ll probably have to reset and talk about that.” - Jeff Thornburg, CEO and Co-Founder of Portal
Support from Strategic Investors
Investors were drawn not only to Portal’s technology but also its dual-use potential across the commercial and defense sectors.
“We were particularly impressed by their Supernova spacecraft, which will improve maneuverability in space by over an order of magnitude, while also significantly extending operational lifespans by enabling a more sustained presence in space,” - Brannon Jones, Investor at AlleyCorp and Former SpaceX Engineer
“With their propulsion system, the future of space will turn from a relatively static ecosystem to one that is dynamic, expressive, and action-oriented,” - Brendan Wales, Founding Partner of FUSE
Emerging From Stealth Mode
Portal Space Systems formally exited stealth mode on April 30, 2024, unveiling its ambitious plans for Supernova alongside $3 million in Department of Defense awards and additional private investment.
The company was founded in 2021 by Jeff Thornburg, formerly head of mechanical engineering and manufacturing for Amazon’s Project Kuiper, and previously senior director of propulsion at SpaceX, where he led the design of the Raptor engine used on Starship.
Thornburg co-founded Portal with Ian Vorbach (Chief Operating Officer) and Prashaanth Ravindran (VP of Engineering), spending the company’s early years immersed in customer discovery, engaging commercial and government users to understand unmet needs in spacecraft mobility and responsiveness.
“I saw the need for mobility solutions that didn’t exist for both commercial and military applications,” - Jeff Thornburg, CEO and Co-Founder of Portal
A Path to the Future of Agile Space Operations
Portal’s emergence and momentum reflect a growing shift in the space industry toward dynamic, on-demand mobility. From satellite servicing and debris avoidance to national security missions requiring repositionable assets, the need for flexible, high-performance spacecraft has never been clearer.
