Most thrusters burn chemicals or accelerate ions electrically. A third path heats propellant with raw sunlight. US12467421B2, granted to Trans Astronautica Corporation on November 11, 2025, pursues it, claiming an "omnivorous solar thermal thruster, cooling systems, and thermal energy transfer in rockets."
The CPC spans propulsion and solar collection: F02K 9/64 (thrust-chamber and nozzle arrangements), B64G 1/401 / 1/402 / 1/446 (propellant tanks, propulsion, solar arrays), F02K 9/42 / 9/44 / 9/60, and a notable run of F24S solar-concentrator codes (F24S 20/20, 23/30, 23/70, 70/16). The F24S solar-thermal-collector codes alongside rocket codes are the unmistakable signature of solar-thermal propulsion.
The mechanism is heat from light. Concentrators focus sunlight onto a heat exchanger or absorber, raising propellant to high temperature; the hot gas then expands through a nozzle for thrust. Solar-thermal propulsion sits between chemical (high thrust, low efficiency) and electric (high efficiency, tiny thrust) — offering moderate thrust at efficiency better than chemical, without the heavy power-processing electronics electric thrusters need. "Omnivorous" propellant tolerance is the strategic twist: a thruster that can use whatever volatile is available is well suited to space-resource and in-situ-propellant ambitions, which is squarely Trans Astronautica's stated focus.
The named inventor, Joel Sercel, recurs across an unusually visionary body of solar-thermal and space-mining filings — the company's portfolio (including US12297792B2 earlier in 2025) is one of the more distinctive in the propulsion landscape for its commitment to sunlight-as-energy architectures.
The honest discipline: solar-thermal propulsion has been studied for decades and flown rarely; this grant protects a specific omnivorous-thruster-plus-thermal-management design, not the concept, and a granted claim is not a demonstrated engine. Read it as a clear marker of a contrarian propulsion bet — using abundant sunlight and flexible propellant — and as a reminder that the gap between an elegant thermal architecture and a working in-space thruster is exactly where such bets are won or lost.