The next frontier in space is closer than you think – welcome to the world of very low Earth orbit satellites

There are approximately 15,000 satellites orbiting the Earth. Most of them, like the International Space Station and the Hubble Telescope, reside in low Earth orbit, or LEO, which peaks about 2,000 kilometers above the Earth’s surface.

But as more satellites are launched into LEO — SpaceX’s Starlink Internet constellation alone will eventually send several thousand more — the region is getting a little crowded.

That’s why it’s fortunate that there is another orbit, even closer to Earth, that promises to help reduce overpopulation. It’s called VLEO, or very low Earth orbit, and is located just 60 to 250 miles (100 to 400 kilometers) above the Earth’s surface.

As an engineer and professor who develops technologies to expand human presence beyond Earth, I can tell you that Very Low Earth Orbit, or VLEO, satellites offer advantages over higher altitude satellites. Among other benefits, VLEO satellites can provide higher resolution images, faster communications and better atmospheric science. Full disclosure: I am also a co-founder and co-owner of Victoria Defense, which seeks to commercialize VLEO and other space energy technologies.

Advantages of VLEO

Images from satellites in very low Earth orbit are sharper because they simply see the Earth more clearly than satellites higher up, much like moving closer to a painting helps you see it better. This translates to higher resolution images for agriculture, climate science, disaster response and military surveillance.

End-to-end communication is faster, which is ideal for real-time communications, such as telephone and Internet services. Although the signals still travel the same speed, they don’t have to go as far, which reduces latency and conversations flow more smoothly.

Most weather forecasts rely on images of clouds above the Earth. Therefore, bringing these images closer together means higher resolution and more data to predict.

Because of these advantages, government agencies and industry are working to develop satellites in very low Earth orbit.

The hold-up: atmospheric drag

You may be wondering why this region of space has so far been avoided for sustained satellite operations. This is for one major reason: atmospheric drag.

Space is often thought of as a void. So where exactly does space begin? Although around 100 kilometers in altitude – known as von Kármán’s line – is widely considered the starting point, there is no difficult transition where space suddenly begins. Instead, as we move away from Earth, the atmosphere becomes thinner.

In and below very low Earth orbit, Earth’s atmosphere is still thick enough to slow satellites, causing those at the lowest altitudes to deorbit within weeks or even days, essentially burning up as they fall back to Earth. To counteract this atmospheric drag and stay in orbit, the satellite must constantly propel itself forward – in the same way that riding a bicycle into the wind requires continuous pedaling.

For propulsion in space, satellites use different types of thrusters, which provide the necessary thrust to avoid slowing down. But in VLEO, the thrusters must be on all or almost all the time. Thus, conventional thrusters would quickly run out of fuel.

Fortunately, Earth’s atmosphere in VLEO is still thick enough that the atmosphere itself can be used as fuel.

Innovative thruster technologies

That’s where my research comes in. At Penn State, in collaboration with Georgia Tech and funded by the U.S. Department of Defense, our team is developing a new propulsion system designed to operate at a height of 43 to 55 miles (70 to 90 kilometers). Technically, these altitudes are even lower than very low Earth orbit, making combating drag even more difficult.

Our approach collects the atmosphere using a spoon, like opening your mouth wide when pedaling a bicycle, then uses high-power microwaves to heat the collected atmosphere. 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 were able to demonstrate a prototype thruster in the laboratory inside a vacuum chamber that simulates the atmospheric pressure found at 80 km altitude.

This approach is relatively simple, but it has potential, particularly at low altitudes, where the atmosphere is thicker. Higher up, where the atmosphere is thinner, spacecraft could use different types of VLEO thrusters that others are developing to cover large altitude ranges.

Our team is not the only one working on thruster technology. Just one example: The U.S. Department of Defense partnered with defense contractor Red Wire to develop Otter, a VLEO satellite with its version of atmospheric breathing thruster technology.

Another option for keeping a satellite in VLEO, which leverages technology I have worked on throughout my career, is to attach a lower orbit satellite to a higher orbit satellite with a long tether. Although NASA has never flown such a system, the proposed follow-up to the Long Cable Satellite System missions carried out in the 1990s was to drop a satellite into a much lower orbit from the Space Shuttle, connected by a very long tether. We are currently re-examining this system to see if it could work for VLEO in a modified form.

Other complications

Overcoming drag, although it is the hardest, is not the only challenge. Satellites in very low Earth orbit are exposed to very high levels of atomic oxygen, a highly reactive form of oxygen that quickly corrodes most substances, even plastics.

The satellite’s materials also must withstand extremely high temperatures, above 2,732 degrees Fahrenheit (1,500 degrees Celsius), because friction heats them as they move through the atmosphere, a phenomenon that occurs when all spacecraft re-enter the atmosphere from orbit.

The potential of these satellites stimulates research and investment, and the proposed missions have become reality. Juniper research estimates that $220 billion will be invested over the next three years alone. Soon your internet connection, weather forecast and security could be even better, powered by VLEO satellites.

This article is republished from The Conversation, an independent, nonprofit news organization that brings you trusted facts and analysis to help you make sense of our complex world. It was written by: Sven Bilén, State of Pennsylvania

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Sven Bilén founder and co-owner of Victoria Defense, which seeks to commercialize VLEO and other space technologies. It receives funding from DARPA and NASA related to VLEO technologies.