Most satellites launch with 500 m/s or less of available delta-v. This allows them to fine-tune their orbits, and perform some basic maneuverability to avoid conjunctions with other satellite or debris. But this is not enough propulsive capability to make meaningful changes to their orbits.
Delta-v for thee
This is where Portal Space believes it has a solution. Thornburg says the company is developing a spacecraft built around the concept of solar thermal propulsion, which uses solar energy to heat propellant and produce thrust. Such engines have been studied for decades, but have never been developed for practical purposes. The company has not disclosed its propellant of choice, but Thornburg said it is storable on orbit, and not toxic like hydrazine. (It might be something like ammonia.)
Since founding Portal in November 2021, Thornburg says he and his team are solving the technical challenges inherent in the system with their Supernova satellite bus. These spacecraft, he said, will pack an impressive amount of mobility—6,000 m/s of delta-v. That’s enough to move from higher orbits to cislunar space and back.
He envisions a fleet of refuelable Supernova vehicles at medium-Earth and geostationary orbit capable of swooping down to various orbits and providing services such as propellant delivery, mobility, and observation for commercial and military satellites. His vision is to provide real-time, responsive capability for existing satellites. If one needs to make an emergency maneuver, a Supernova vehicle could be there within a couple of hours.
“If we’re going to have a true space economy, that means logistics and supply services,” he said.
Developing a spacecraft with a novel propulsion system and an enormous amount of delta-v capability may sound ambitious, especially for a small startup. However, Thornburg has some credible experience, having worked in the military, for NASA, and at various space companies, including SpaceX, where he was a vice president of propulsion and a lead designer of the Raptor rocket engine.
Portal Space announced Thursday that it has received $3 million in funding from the US Space Force to support development of the Supernova satellite bus. Thornburg said the company plans to launch its first satellite toward the end of 2025 or in early 2026. It will likely go to medium-Earth orbit and, at a minimum, demonstrate its large delta-v capability.