Rapid Maneuverability, with Jeff Thornburg (CEO of Portal Space Systems)

Jeff Thornburg helped build Raptor at SpaceX. Now he’s building something new: a spacecraft designed for rapid maneuverability across orbits powered by solar thermal propulsion. In this episode of Valley of Depth, we get into the technical, strategic, and commercial implications of in-space mobility and why it matters now. Topics include: The hardest parts of building a rocket engine (and why most startups get it wrong) The origins of the Raptor engine and lessons from SpaceX Why Portal is betting on solar thermal propulsion How Supernova enables fast, responsive movement across LEO, MEO, and GEO The case for refueling in orbit and designing without dependencies Why defense needs faster spacecraft and what commercial use cases follow How Thornburg sees Starship changing the economics of space and much more… • Chapters • 00:00 – Intro 01:44 – What drew Jeff to creating engines? 05:13 – Why is building rocket engines still so difficult? 11:50 – Jeff's time at SpaceX 17:52 – Stratolaunch and Commonwealth Fusion and why Jeff moved on 22:50 – Origin of Portal 25:25 – Commercial use case 27:00 – 5 year vision for Portal's architecture 32:01 – Pricing 34:52 – Solar thermal propulsion 38:14 – What comes after Portal's Supernova? 41:15 – Customer traction and Supernova flight 45:44 – Competition in solar thermal propulsion 49:20 – Fundraising prior to the first launch 51:18 – Portal in the next 10 years 54:53 – State of Starship • Show notes • Jeff’s socials — https://x.com/JeffThornburg Antares’ socials — https://x.com/PortalSpaceSys Antares’ website — https://www.portalsystems.space/ Mo's socials — https://twitter.com/itsmoislam Payload’s socials — https://twitter.com/payloadspace / https://www.linkedin.com/company/payloadspace Ignition’s socials — https://twitter.com/ignitionnuclear / https://www.linkedin.com/company/ignition-nuclear/ Tectonic’s socials — https://twitter.com/tectonicdefense / https://www.linkedin.com/company/tectonicdefense/ Valley of Depth archive — Listen: https://pod.payloadspace.com/ • About us • Valley of Depth is a podcast about the technologies that matter — and the people building them. Brought to you by Arkaea Media, the team behind Payload (space), Ignition (nuclear energy), and Tectonic (defense tech), this show goes beyond headlines and hype. We talk to founders, investors, government officials, and military leaders shaping the future of national security and deep tech. From breakthrough science to strategic policy, we dive into the high-stakes decisions behind the world’s hardest technologies. Payload: www.payloadspace.com Ignition: www.ignition-news.com Tectonic: www.tectonicdefense.com