Viridian Space’s Air Breathing Electric Propulsion Solution Enables Sustained VLEO Missions, Operating LEO Missions That Refuel At VLEO, and Capital-Efficient Economics For New Mission Archtypes
Space has traditionally had 6 different types of orbits available to satellites: LEO, MEO, GEO, HEO, SSO, and Polar. Low Earth Orbits typically operate from altitudes of around 400 km to 2000 km, Mid Earth Orbit from roughly 2000 km to 32000 km, and Geostationary Earth Orbits at roughly 35000 km. Highly Elliptical Orbits are rare and vary wildly in their mission parameters. Sun Synchronous Orbits are a specific type of Polar Orbit, both of which are functionally LEO orbits between 500-1000 km altitude. To pair things down and simplify, that means that we’ve got LEO, MEO, and GEO for everything close to earth, a bit away from earth, and really far out there respectively. Viridian’s Air Breathing Electric Propulsion solution opens up entirely new real estate for satellites and mission architectures: Very Low Earth Orbit. The VLEO range typically falls between 150-350 km and is low enough that atmospheric drag adversely affects the performance of a spacecraft. Objects at this altitude have always been referred to as decaying because they’re simply not moving fast enough to overcome the Earth’s gravitational pull, and the atmospheric drag only slows them down further. So how has Viridian’s ABEP solution changed things and unlocked these altitudes for operation?
Viridian’s technology on a fundamental level allows for satellites to capture atmospheric gas at VLEO, compress and store that gas, and then use it as fuel for their vehicle, expending it for thrust. The quick math for this type of equation boils down to “The Goezinta” method: The Goezinta has to equal the Goezoutta. In so many words, a satellite on orbit in VLEO will run into air. If that air simply bangs into the satellite and bounces off, that satellite will slow, conserving momentum between the satellite and the air that hits it. Now, if we capture all of that air, and hold onto it, the satellite will still slow down, as the mass of the air will combine with the mass of the satellite, and the new total mass will still need to conserve momentum. So, in order to maintain velocity, whatever air ‘goes into’ the satellite, will have to ‘go out of’ the satellite at the same velocity. If the satellite ‘captures’ 100% of the air it hits, this ratio is 1:1. If the satellite captures less than 100%, then the air leaving the satellite will have to go faster. Catching 50% of the air means that the air leaving the satellite will have to move at 2x its inlet velocity, and so on. Viridian’s approach allows them to capture almost 100% of the air the satellite encounters, and expel it faster than it was caught. They can create additional thrust from capturing air, which is their consumable prop fuel.
This does several things. First, it means that their vehicles can literally refill their gas tanks. Current mission CONOPS are designed around the life of the asset fully depreciating and being expended when the consumable fuel runs out. When the gas light comes on in your car, you drive it off the road and buy a new car. That’s a great starting point if that’s the only way you can drive, but it’s a super inefficient and wasteful model. Viridian’s platform means that you can instead get off the highway, head to a gas station, fill up, and then get back on the highway. You can drive until the engine breaks, the wheels fall off, or you finally make it across Route 66.
Obviously, this opens a lot of doors. It means that satellites can operate at LEO, dive down to VLEO to refuel, and then continue back to their operating altitude in LEO, effectively extending their operating life. It means that the annual cost / depreciation of a satellite’s value slows by the increase in its mission life. It means that the capital requirements for building a satellite and executing a mission go down substantially. It grows the market, opening the door to new players and new entrants into the space. But the possibilities of this capability don’t stop at the simple economics. Since the satellite can fuel or refuel at VLEO altitudes and make its way back to LEO independently, it means that your asset can launch on a smaller launch provider that doesn’t need to reach an insertion altitude of 500 km. It means that the launch bottleneck will also see benefits, as demand for launch can shift from LEO orbit insertion to VLEO orbit insertion which is cheaper and easier to achieve. But all of this represents only the implications of one of the mission archtypes Viridian can unlock: operating at LEO and refueling at VLEO.
There’s also the entire model of launching and operating sustainably at those VLEO altitudes. “There’s huge benefits to flying and staying in VLEO because if you’re lower in altitude – we’re talking … down to 150 km or so – you’re talking about one third the distance, so images are much closer and sharper. Also, the amount of power for communication purposes and SAR goes way down… so you get economies of scale by downsizing these payloads.” – Matthew Feldman, Founder and CTO. “There’s a really big benefit to designing a mission to operate and live fully at VLEO, though not all missions will be optimal for such a plan; others will be better served by optimizing to operate at LEO and refuel at VLEO.” Viridian’s recent awards from the NSF and SBIRs reflect both the confidence in their technological approach and the desire for Viridian to continue growing and to provide their capabilities more broadly to commercial and defense markets. They’re not the only ones playing in the VLEO space, as international investment in the space has grown over the past year. Viridian will have to move quickly and continue to execute well in order to help the US maintain a competitive edge in the segment. To do so, the team is growing rapidly – looking for talented and passionate engineers to join the team. If you’re interested in learning more about Viridian’s open opportunities or designing around their capabilities and product offerings, they want to hear from you!
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