{"id":17076,"date":"2025-11-25T20:57:08","date_gmt":"2025-11-25T12:57:08","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/uncommon-thinkers-how-portals-jeff-thornburg-plans-to-harness-the-heat-of-the-sun-in-the-cold-of-space\/"},"modified":"2025-11-25T20:57:08","modified_gmt":"2025-11-25T12:57:08","slug":"uncommon-thinkers-how-portals-jeff-thornburg-plans-to-harness-the-heat-of-the-sun-in-the-cold-of-space","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/uncommon-thinkers-how-portals-jeff-thornburg-plans-to-harness-the-heat-of-the-sun-in-the-cold-of-space\/","title":{"rendered":"Uncommon Thinkers: How Portal\u2019s Jeff Thornburg plans to harness the heat of the sun in the cold of space"},"content":{"rendered":"
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Portal Space Systems CEO Jeff Thornburg checks out the vacuum chamber where space hardware is tested. (GeekWire Photo \/ Alan Boyle)<\/figcaption><\/figure>\n

Editor\u2019s note:<\/strong> This series profiles six of the Seattle region\u2019s <\/em>\u201cUncommon Thinkers\u201d<\/em>: inventors, scientists, technologists and entrepreneurs transforming industries and driving positive change in the world. They will be recognized Dec. 11<\/em><\/em> at the <\/em>GeekWire Gala<\/em>. Uncommon Thinkers is presented in partnership with<\/em> Greater Seattle Partners<\/em>.<\/p>\n

BOTHELL, Wash. \u2014 Before he became the CEO of Portal Space Systems, Jeff Thornburg worked for two of the world\u2019s most innovative space-minded billionaires. Now he\u2019s working on an idea those billionaires never thought to pursue: building a spacecraft powered by the heat of focused sunlight.<\/p>\n

Thornburg and his teammates are aiming to make Bothell-based Portal the first commercial venture to capitalize on solar thermal propulsion, a technology studied decades ago by NASA and the U.S. Air Force. The concept involves sending a propellant through a heat exchanger, where the heat gathered up from sunlight causes it to expand and produce thrust, like steam whistling out of a teakettle.<\/p>\n

\"Uncommon<\/figure>\n

The technology is more fuel-efficient than traditional chemical propulsion \u2014 and faster-acting than solar electric propulsion, which uses solar arrays to turn sunlight into electricity to power an ion drive. Solar thermal propulsion nicely fills a niche between those two methods to move a spacecraft between orbits. But neither NASA nor the Air Force followed up on the concept.<\/p>\n

\u201cThey didn\u2019t abandon it for technical reasons,\u201d Thornburg said. At the time, it just didn\u2019t make economic or strategic sense to take the concept any further.<\/p>\n

What\u2019s changed?<\/p>\n

\u201cLower launch costs, coupled with additive manufacturing, are the major unlocks to bring the tech to life, and make it affordable and in line with commercial development,\u201d Thornburg said.<\/p>\n

Thornburg argues that it\u2019s the right time for Portal\u2019s spacecraft to fill a gap in America\u2019s national security posture on the high frontier. \u201cThere was no imperative for rapid movement on orbit in the 1990s,\u201d he said. \u201cOnly recently have the threats from our adversaries highlighted the weaknesses in current electric propulsion systems, in that they have so little thrust and can\u2019t enable rapid mobility.\u201d<\/p>\n

Portal\u2019s vision has attracted interest \u2014 and financial support \u2014 from investors and potential customers. Since its founding in 2021, the startup has raised more than $20 million in venture capital. In 2024, Portal won a commitment for $45 million in public-private funding from SpaceWERX, the innovation arm of the U.S. Space Force. And next year, Portal is due to demonstrate its hardware for the first time in orbit.<\/p>\n

So, how did Thornburg hit upon the idea of turning a decades-old idea into reality?<\/p>\n

The path to propulsion<\/h3>\n

Thornburg, who\u2019s now 52 years old, has focused on making things fly for most of his career. It all started when he was a college student in Missouri in the early 1990s, earning his aerospace engineering degree with an ROTC scholarship from the Air Force. He recalled a conversation he had with an instructor who was an old F-4 fighter pilot.<\/p>\n

\u201cWith my nearsightedness, I was out of the game from a pilot standpoint,\u201d Thornburg said. \u201cBut he said, \u2018Thornburg, if you can\u2019t fly the planes, go be as close to them as you can.’\u201d<\/p>\n

Thornburg signed up for a program that fast-tracked him into an aircraft maintenance role. He traveled around the world with KC-135 cargo planes, supporting missions that included the NATO-led air campaign against Yugoslavia in 1999. During his time as a flight commander and aircraft maintenance officer at MacDill Air Force Base in Florida, \u201cI had a couple of hundred enlisted people who worked hard to keep me out of trouble,\u201d he said.<\/p>\n

The Air Force is where he earned his master\u2019s degree in aerospace engineering. \u201cMy adviser had a friend that worked at the Air Force Research Lab,\u201d Thornburg recalled. \u201cHe called him and said, \u2018The Air Force is about to send this guy to do something with airplanes, but I\u2019m pretty sure he\u2019s going to be disappointed if he can\u2019t come out and work on rocket engines.’\u201d<\/p>\n

Sure enough, Thornburg was soon working on rocket propulsion development, including a project to create what\u2019s known as a full-flow staged combustion cycle engine. \u201cWe made what people thought was not possible possible with that program,\u201d Thornburg said.<\/p>\n

In 2004, Thornburg left the Air Force to work on rocket propulsion systems at Exquadrum, Aerojet and NASA. Then, in 2011, he took a phone call from SpaceX\u2019s billionaire founder, Elon Musk. \u201cWe talked for about an hour, hour and a half on the phone \u2014 and he said, \u2018I\u2019ve got a project I want to talk to you about,’\u201d Thornburg said.<\/p>\n

That project led to the development of SpaceX\u2019s methane-fueled Raptor rocket engine, which leveraged the technology that Thornburg helped pioneer at the Air Force. \u201cThat was a wild ride, because that felt like about 15 or 20 years of experience in a five-year time period,\u201d he recalled.<\/p>\n

\"Jeff
Jeff Thornburg strikes a pose in front of a test stand at NASA\u2019s Stennis Space Center during his time as vice president of propulsion engineering at Stratolaunch. (Stratolaunch Systems Photo \/ 2018)<\/figcaption><\/figure>\n

After five years at SpaceX, Thornburg needed to wind down. He decided to do some consulting at his home base in Huntsville, Alabama, also known as Rocket City. \u201cAbout six months in, I\u2019m like, I need a real job again,\u201d he said. \u201cAnd some friends of mine introduced me to, ultimately, Paul Allen. Paul called me and said, \u2018Can you come out to my Seattle office?’\u201d<\/p>\n

The Microsoft co-founder and software billionaire enlisted Thornburg to become the head of rocket propulsion development for Stratolaunch, Allen\u2019s space venture. Thornburg led the effort to create a liquid rocket engine known as the PGA \u2014 which stood for \u201cPaul G. Allen.\u201d<\/p>\n

Unfortunately, Allen passed away in 2018, just one month after the engine was unveiled. Under new ownership, Stratolaunch pivoted to hypersonic testing, and the PGA project fell by the wayside. Once again, Thornburg and his family hunkered down in Huntsville.<\/p>\n

Building a business<\/h3>\n

\u201cI decided to start my first space company after Paul died,\u201d Thornburg said. \u201cI focused on hydrogen propulsion technology and solutions, kind of like what we were working on for Paul.\u201d<\/p>\n

That first company, Interstellar Technologies, started working on projects for NASA, Northrop Grumman and a couple of other customers. Then the pandemic hit. \u201cThe investors that were about to provide funding disappeared,\u201d Thornburg said. \u201cNASA went home, Northrop Grumman went home. And so I had to find my small team other jobs.\u201d<\/p>\n

Just as Thornburg was about to resign himself to riding out the pandemic in Alabama, Amazon\u2019s recruiters called. They asked him to move to Seattle to run engineering and manufacturing for Project Kuiper, the satellite internet project that\u2019s now known as Amazon Leo. \u201cThat\u2019s ultimately what got us moved to Seattle,\u201d Thornburg said.<\/p>\n

His yearlong stint at Amazon was long enough to establish the process for building Project Kuiper\u2019s two prototypes and the production-grade satellites that came after them. Then he took on engineering management roles at Agility Robotics and Commonwealth Fusion Systems.<\/p>\n

That\u2019s when Portal Space Systems took shape.<\/p>\n

\"Ribbon-cutting
VIPs cut the ribbon at Portal Space Systems\u2019 HQ in Bothell, Wash., in March 2025. From left: U.S. Rep. Suzan DelBene; Portal co-founders Prashaanth Ravindran, Jeff Thornburg and Ian Vorbach; and Bothell Mayor Mason Thompson. (GeekWire Photo \/ Alan Boyle)<\/figcaption><\/figure>\n

To be fair, the seeds for Portal were planted back in 2016, just weeks after Thornburg left SpaceX. \u201cLawrence Livermore Lab had called and said, \u2018We\u2019re doing a seminar on the future of propulsion. Would you like to come be a speaker?’\u201d he recalled. \u201cI said, \u2018Yes, what do you want me to talk about?\u2019 They said, \u2018We want you to tell us what the future of propulsion looks like.\u2019 Oh my gosh, no pressure on that!\u201d<\/p>\n

As he did the research for his talk, he came across the idea of putting a nuclear reactor on a spacecraft, and using the concentrated heat from that reactor to blast a propellant through a thruster. The concept, known as nuclear thermal propulsion, seemed like a stretch \u2014 but then Thornburg had an uncommon thought.<\/p>\n

\u201cCan you concentrate solar energy to heat a thrust chamber and do the same thing?\u201d Thornburg said. \u201cYou can. It\u2019s not quite as effective as a nuclear reactor, for obvious reasons, but it\u2019s all the same pieces. \u2026 Now I don\u2019t have to wait on a low-cost, low-weight, space-rated nuclear reactor that doesn\u2019t exist yet.\u201d<\/p>\n

Thornburg mulled over the idea for years. \u201cI was thinking about Portal, and I was starting the beginnings of Portal in 2021, but I still had to pay the bills,\u201d he said. For a couple of years, he worked during the day at Agility Robotics and Commonwealth Fusion \u2014 and spent nights and weekends laying the groundwork for the startup.<\/p>\n

\u201cWhen Portal could really start to stand on its own, as we started to win over the Defense Department, that\u2019s when I made the switch with all of my time focused on what was going on in Portal,\u201d Thornburg said. In April 2024, the startup emerged from stealth and announced it had received more than $3 million in funding from the Defense Department and the Space Force.<\/p>\n

The road ahead<\/h3>\n

Portal\u2019s flagship vehicle is called Supernova. It\u2019s a rapid-transorbital, multi-mission vehicle that should be capable of moving itself and its payloads from one orbit to another \u2014 even from low Earth orbit to geostationary Earth orbit, more than 20,000 miles higher up. And it should be able to do that within hours or a day, rather than the weeks or months that are typically required.<\/p>\n

The spacecraft itself will be about the size of a restaurant refrigerator. To concentrate sunlight on its heat exchanger and thruster system, Supernova will use sheets of reflective material that can unfold to a width of roughly 55 feet. Ammonia will serve as the propellant. The 3D-printed heat exchanger thruster, dubbed Flare, was successfully tested earlier this year.<\/p>\n

Next year\u2019s orbital demonstration will involve putting an instrument package known as Mini-Nova, which is about the size of a tissue box, on a satellite platform that\u2019s due for launch on a SpaceX rideshare mission. The demonstration is meant to validate Supernova\u2019s system design.<\/p>\n

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Portal CEO Jeff Thornburg holds a Mini-Nova model that carries the signatures of Thornburg and teammates who worked on the project. (GeekWire Photo \/ Alan Boyle)<\/figcaption><\/figure>\n

In late 2026, Portal plans to send up a free-flying spacecraft called Starburst, which will be equipped with thrusters powered by an electrothermal heating system. Starburst won\u2019t be as powerful as Supernova, but it will provide Portal\u2019s customers with an early option for rapid maneuverability in orbit. If next year\u2019s test goes well, Starburst is expected to start taking on customer missions in 2027.<\/p>\n

2027 is also the year when Supernova is scheduled to make its debut. All of the development work for Supernova and Starburst will be taking place at Portal\u2019s 8,000-square-foot lab and 50,000-square-foot manufacturing facility in Bothell.<\/p>\n

Throughout Portal\u2019s formative years, Thornburg has worked with fellow members of the \u201csmall team\u201d he assembled at Interstellar Technologies. Both of Portal\u2019s other co-founders \u2014 chief operating officer Ian Vorbach and engineering vice president Prashaanth Ravindran \u2014 crossed paths with Thornburg at Interstellar, and at Stratolaunch before that.<\/p>\n

Vorbach, whose background includes startup experience as well as engineering experience, said Portal\u2019s business model has been fine-tuned to make sure it addresses the needs of its target market. He and Thornburg identified the U.S. military\u2019s need for tactical responsiveness in space as the top priority.<\/p>\n

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Portal Space Systems is working on two types of orbital transfer vehicles: Supernova, which uses large mirrors to concentrate sunlight on a heat exchanger \/ thruster system (at left); and Starburst (at right), a smaller spacecraft that leverages many of the technologies developed for Supernova. (Portal Space Systems Illustrations)<\/figcaption><\/figure>\n

\u201cWhat happens a lot in the space industry is that you have incredibly technical, talented people who have a technology that provides some very unique performance, and then they build it, and it turns out that performance isn\u2019t needed,\u201d Vorbach said. \u201cThere\u2019s got to be a reason to bring that innovation to market.\u201d<\/p>\n

Vorbach is grateful for Thornburg\u2019s leadership. \u201cWe work very long hours, but I think Jeff does a great job of making sure people know that they\u2019re valued,\u201d he said. \u201cI appreciate that, and I think it\u2019s why we, fortunately, are able to hire great talent from the places he\u2019s come from, whether it\u2019s SpaceX or Kuiper.\u201d<\/p>\n

Ravindran, who worked at Jeff Bezos\u2019 Blue Origin space venture before taking a founder\u2019s role at Portal, agreed with that assessment. \u201cIt\u2019s always amazing to have someone like Jeff out there, because he\u2019s come up the engineering road to realize our pain points as well, and he doesn\u2019t try to hold us to unfair standards,\u201d he said. \u201cThat way, we are not set up for failure.\u201d<\/p>\n

Stan Shull, a space industry analyst at Bellevue, Wash.-based Alliance Velocity, gives Portal high marks. \u201cIn space terms, a highly maneuverable satellite is said to have high delta-V,\u201d he told GeekWire in an email. \u201cPortal, as a company, feels high delta-V too.\u201d<\/p>\n

Thornburg\u2019s experience and expertise are big factors behind Portal\u2019s rapid progress, Shull said. \u201cHe\u2019s very knowledgeable about national security issues and is a straight shooter about the growing threat environment in orbit,\u201d he said. \u201cIt\u2019s no surprise the Space Force is among the many customers interested in what the company is up to.\u201d<\/p>\n

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