The Growing Importance of Very Low Earth Orbit Satellites

Currently, there are approximately 15,000 satellites in orbit around the Earth. Many of these, such as the International Space Station and Hubble Telescope, are located in what’s known as low Earth orbit (LEO), which extends up to about 1,200 miles (2,000 kilometers) above the planet.

However, with the increasing number of satellites—especially with initiatives like SpaceX’s Starlink internet constellation planning to deploy thousands more—the LEO environment is becoming quite congested.

Fortunately, there’s another layer to explore, closer to Earth, which could ease this overcrowding: very low Earth orbit (VLEO), ranging from just 60 to 250 miles (100 to 400 kilometers) above the surface.

As an engineer and professor focused on advancing human technology in space, I see several advantages for satellites placed in VLEO. For starters, they can capture higher-resolution images and facilitate improved communications and atmospheric studies. It’s worth mentioning that I’m also a co-founder of a company called Victoria Defense, which aims to capitalize on VLEO technologies.

Advantages of VLEO

Essentially, images from satellites in VLEO are clearer because they are closer to the Earth—similar to how being near a painting lets you see its details better. This clarity can greatly benefit fields like agriculture, climate science, disaster response, and military monitoring.

Moreover, VLEO satellites can enable quicker communications. Even though signals travel at the same speed, they don’t have to traverse as much distance, which means less lag time. This setup is perfect for services needing real-time interaction, like phones and internet.

Additionally, better weather forecasting is often reliant on cloud imagery from above, and capturing those images from a lower altitude means better resolution, offering more precise data.

Due to these advantages, both government organizations and industry players are keen on developing VLEO satellite technologies.

Challenges of Atmospheric Drag

Now, you might wonder why VLEO hasn’t been more widely utilized for satellite operations. The central issue is atmospheric drag.

Space isn’t a pure vacuum. While the von Kármán line at around 62 miles (100 kilometers) is often thought of as the boundary to space, there isn’t a definitive point at which the atmosphere disappears. As you ascend, the air simply becomes less dense.

In the realm of very low Earth orbit, the atmosphere still exerts enough drag to slow satellites down significantly. This means that those operating at the lowest altitudes can deorbit in a matter of weeks—or even days—burning up during their descent. To maintain their orbit, satellites must continuously thrust forward, similar to how pedaling a bike against the wind requires effort.

Satellites utilize various thruster systems to generate the necessary momentum. However, at these low altitudes, they would need thrusters operational nearly all the time, which would lead to quick fuel depletion.

The silver lining? The atmosphere in VLEO is dense enough that the ambient air can actually serve as a propellant.

Innovative Propulsion Technologies

This is where my research at Penn State comes in, in partnership with Georgia Tech and with funding from the U.S. Department of Defense. Our team is developing a specialized propulsion system designed to operate at altitudes between 43 and 55 miles (70 to 90 kilometers). These altitudes happen to be even lower than VLEO, making the challenge all the more complex due to drag.

We’ve conceptualized a method that captures atmospheric particles using a scoop—imagine catching air in your mouth as you cycle—and then uses high-powered microwaves to heat up the collected air. By expelling the heated gas through a nozzle, this thrusts the satellite forward. We refer to this approach as an air-breathing microwave plasma thruster, and we’ve already tested a prototype in a lab environment simulating the pressure found at 50 miles (80 kilometers) high.

This method, while relatively straightforward, shows promise, particularly at lower altitudes where the atmosphere is more abundant. For higher altitudes, satellites could employ different thruster types that other teams are also exploring.

Our efforts are not isolated; for example, the U.S. Department of Defense has partnered with a contractor to develop its version of atmosphere-breathing propulsion technology for VLEO satellites.

Another interesting concept is connecting a lower-orbit satellite to a higher one via an extensive tether. Although NASA hasn’t executed such a system in the past, the idea was proposed for future missions following the Tether Satellite System trials during the 1990s. We’re currently revisiting this concept, exploring its viability for VLEO.

Other Complications

Despite drag being a significant hurdle, it’s not the only concern. Satellites at VLEO encounter high levels of atomic oxygen, a reactive variant of oxygen that can rapidly corrode many materials, including some plastics.

The materials used for satellites also have to endure extreme temperatures—over 2,732 degrees Fahrenheit (1,500 degrees Celsius)—due to friction as they move through the atmosphere when reentering from orbit.

The potential for VLEO satellites continues to drive investment and research. Proposals are becoming realities, with estimates suggesting that around $220 billion could be directed into this sector over the next three years. This innovation could dramatically enhance internet connectivity, weather forecasting, and security systems, all powered by VLEO technology.