As low Earth orbit becomes more crowded, requires more avoidance maneuvers, and threatens debris cascades, some researchers are looking to new frontiers to deploy a next generation of designs. One of those is very low Earth orbit (VLEO), which could have satellites orbiting at just 43 miles from Earth’s surface—though at that height, they’d need to contend with extreme atmospheric drag and overheating, requiring a complete redesign of how satellites are built.
Various companies are developing these satellite designs, and their potential is substantial. Although there are significant challenges at such an orbital altitude, such satellites could deliver much higher-resolution imagery of Earth and weather patterns, provide even lower-latency, higher-bandwidth internet connections, and offer unique military applications.
As a Phys.org op-ed by Victoria Defense co-owner Sven Bilén highlights, developing hardware for VLEO deployment entails significant challenges. One is immense atmospheric drag, especially at the speeds an orbiting satellite would need to maintain at that height: as high as 17,000 miles per hour. Without constant thrust, there’s no way to maintain that kind of orbit, so Bilén and his company have designed an atmospheric thruster that would heat up the atmosphere itself to use as fuel.
“Our approach collects the atmosphere using a scoop, like opening your mouth wide as you pedal a bike, then uses high-power microwaves to heat the collected atmosphere,” Bilén describes. “The heated gas is then expelled through a nozzle, which pushes the satellite forward. Our team calls this concept the air-breathing microwave plasma thruster. We’ve been able to demonstrate a prototype thruster in the lab inside a vacuum chamber that simulates the atmospheric pressure found at 50 miles high.”
Another company developing VLEO satellites is Redwire, which has won a DARPA contract for its SabreSat design.
Credit: Redwire
The second major challenge is heat. Even if such a thruster can maintain its speed and altitude to sustain orbit, it’ll generate significant heat, akin to a constant atmospheric re-entry. It would require a chassis and shielding system (potentially non-ablative if it is to remain in orbit for a very long time) that can withstand a constant temperature of 1,500 degrees Celsius (2,732 degrees Fahrenheit).
Then there are problems for Earth-bound telescopes to consider. Starlink satellites are already an issue: Imagine a new fleet of thousands of satellites even closer and burning bright as they transit the sky. It’s difficult not to imagine that it would completely ruin many Earth-based observatories.
Additional challenges include providing power to satellites that can’t deploy large solar arrays, atomic oxygen bombardment at that altitude, and national airspace constraints. Do countries really want hundreds of foreign satellites flying so close to their airspaces?
But the potential is enticing. As LEO becomes increasingly crowded, finding a new orbit for satellite placement will become increasingly important. Combine that with the capabilities of satellites at this altitude, and it’s likely we’ll see VLEO satellites in the future—assuming the challenges can be met.
