New Space Startup Aiming to Solve Changing Orbits

For the entire space age, going back to the late 1950s, the vast majority of satellites have been launched into space with virtually no propellants. The extent of their ability to move has been small movements with small thrusters - primarily station keeping, that is maintaining their position and orientation. 

It has often been said that once a satellite achieves its desired orbit, it's not going anywhere. That's because the energy needed to make significant changes to one's orbit is very high.

In space today, the current choices of on-orbit maneuverability are not optimal. There are conventional rocket-powered thrusters that require an extraordinary amount of propellant to move around. There are ion thrusters, which are significantly more fuel-efficient, but cannot make changes quickly. And that's really about it.

You've long heard the saying, "space is hard" and this is a shining example of that. Changing velocity, usually referred to by the more or less mathematical shorthand "delta-v," is the way orbits get changed. More than that, it's how one can get around the solar system, or from Earth orbit to a different Solar orbit.

But a new company, Portal Space Systems, emerged from stealth on Tuesday with an alternative: solar-thermal propulsion. The company's founder, Jeff Thornburg, said Portal Space will focus on mobility in orbit.

"All propulsion has historically been designed for station keeping for satellites, not maneuverability," he said in an interview. "And too many commercial and military customers are struggling with how to spend the very little delta-v they have before they end the life of their asset."

"Delta-v" is how the space industry measures the change in velocity that a spacecraft is capable of—more precisely, it is a measure of the impulse per unit of spacecraft mass. So if your spacecraft has a delta-v capability of 500 meters per second (1,120 mph), and starts at a velocity of zero, then after it burns all of its propellant it would be traveling at 500 m/s.

You know the saying that the first step is the hardest and it applies in extreme to getting around in space. 

It requires an extraordinary amount of delta-v to go from the surface of our planet into low-Earth orbit (LEO)—very nearly 10,000 m/s. This is why powerful rockets are needed to launch satellites. After reaching LEO, the relative delta-v costs to go places from there are lower, but still high. For example, it costs another 6,000 m/s to reach the surface of the Moon from LEO.

Note that most satellites are capable of 500 m/s delta-v, or less, compared to that 6,000 to get to the moon.

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.)

For most of the three years since the company was founded in 2021, the small crew of just Thornburg and his cofounders Ian Vorbach and Prashaanth Ravindran, has been working on the engineering of the engines they envision. Turning the vision into hardware.  There are ~25 employees supporting Portal now, per Thornburg, and the company’s plans for growth over the next year are aggressive. 

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.

To Thornburg's statement that a true space economy means logistics and supply services, I would add the ability to repair satellites on orbit and refuel the ones that are exhausting their maneuvering fuel. A long way of saying maintenance. 

Concept drawing of a possible Supernova spacecraft design. Image credit: Portal Space Systems

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.
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“Our DoD customers have said they have real needs that really need to get met by 2026,” Thornburg said. “So…how can we accelerate this capability that the warfighter says they want as fast as possible to meet some of the needs that they’re looking at here in the next couple of years?”