By Dr. Gary Deel, Ph.D., JD
Faculty Director, School of Business, American Military University
For satellite launches, there are a variety of orbit types from which mission designers can choose. The optimal choice will usually depend largely on the purposes and functions of the satellites being launched.
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Typically, communications satellites use many different orbits, including Low-Earth Orbits (LEO) and Geosynchronous Orbits (GSO). However, Elon Musk’s SpaceX is planning to utilize an extremely low orbit range for their proposed Starlink communications constellation. As a result, this tactic will present a considerable challenge for other telecom companies by improving SpaceX’s communication speeds.
The Advantages and Disadvantages of Different Satellites and Their Orbits
GSO trajectories have an altitude of roughly 35,786 kilometers. This is the altitude (and corresponding speed) at which a satellite needs to travel in order for the orbital period (the time it takes to complete one full orbit) to equal 24 hours. So GSO satellites orbit the Earth at the same speed at which the Earth turns.
GSO satellites always orbit at the same altitude (35,786 kilometers), but they can conceivably orbit in any direction. For example, you could have a GSO satellite that orbits at a 90-degree inclination, meaning it orbits over the poles (north to south and south to north).
No matter what inclination an orbit adopts, a GSO satellite will always take 24 hours to complete one full orbit. As a result, it will always pass over the same points on the Earth during each rotation.
One specific type of GSO is called a Geostationary Equatorial Orbit (GEO). A GEO is a special type of GSO with an inclination at zero degrees, meaning that its orbit follows the direction of the rotation of the Earth. As such, a satellite in a GEO orbit remains permanently fixed over the same exact spot on the Earth as Earth rotates.
There are advantages to GSO satellites. First, at GSO altitude, satellites can see much more of the Earth, meaning far fewer of them are needed for complete global coverage. In fact, one GSO satellite can see a full 42% of the Earth’s surface from its vantage point. As a result, these satellites are great for applications such as weather monitoring and surveillance.
Another advantage — this one specific to the GEO type satellite — is constant communications ability. With GEO satellites, movable antennae are not needed down here on Earth, because the satellite is always in the same place in the sky.
But there are also disadvantages to GSO satellites. First, to achieve these higher orbits, much more powerful and expensive rockets are needed to supply the lift into space.
Second, the power needed to relay communications is much greater because of the distance. This means that GSO satellites are more robust and expensive to build.
Third, the distance significantly increases the delay associated with signal relays. Light travels fast, but it doesn’t travel infinitely fast.
In fact, a roundtrip signal relay to and from geosynchronous orbital altitude (i.e. a ‘single hop’) can take anywhere from a quarter-second to a half-second. That doesn’t sound like much, but consider that two roundtrips to orbit are actually required for any kind of two-way communication, since the satellite simply acts as a relay between ground-based parties. So the total minimum relay time for an exchange of messages is closer to a full second.
Additionally, sometimes a signal needs to be relayed across multiple satellites in a constellation to make it from sender to recipient and back again. This can add considerable latency.
There are also other delays to consider in communications networks, including cable lengths, routers, switches and other processing points. So what starts off as a mere one-second delay could turn into much more by the time the entire process is completed.
Finally, although GEO satellites are great for equatorial coverage, they have limited visibility with respect to extreme northern and southern latitudes because of the curvature of the Earth.
The other primary orbit type is LEO, which includes altitudes between 160 and 2,000 kilometers. The first advantage to LEO satellites is that because their orbits are so close to Earth relative to GSO orbits, the rockets needed to launch them are generally smaller and cheaper. Less power and fuel are needed for the shorter trip.
Second, because of the lower altitude, LEO satellites require much less power to support communications.
Third, the delay between signals is considerably less than it is for satellites that are much further away. Having the satellite constellation closer to Earth (by more than an order of magnitude when compared with GSO satellites) makes a big difference in communications relay time.
Instead of a second’s worth of delay, for instance, average LEO latency is in the ballpark of a few thousandths to a few hundredths of a second. For this reason, a lot of mobile telecommunications companies utilize LEO constellations.
However, LEO trajectories have their disadvantages as well. First, because LEO satellites are so close to the Earth, they cannot provide nearly as much coverage per satellite as a constellation orbiting much further away.
To provide a constant line of sight for functions like telecommunications, an LEO satellite constellation requires many more satellites. This ensures that there is always a satellite overhead within line of sight of someone at any given point on the surface of the Earth.
Provided that launching hundreds or thousands of LEO satellites in a network is financially feasible, another disadvantage is that the satellites are constantly moving in the sky. Consequently, receivers and transmitters must either be omni-directional or constantly changing their orientations (i.e. tracking) to point toward the locations of the satellites.
SpaceX Plans to Deploy Some Satellites at Very Low Earth Orbits and Increase Communication Relay Times
Over the next several years, SpaceX plans to launch roughly 12,000 satellites in the LEO range at three distinct altitudes for their Starlink data communications constellation. Some satellites will orbit at a range of 1,150 kilometers, which is a common altitude for other telecommunications networks.
In an unusual move, however, SpaceX also plans to deploy large portions of their satellite constellation into altitudes of 340 and 550 kilometers. These ranges are extremely low and are commonly grouped in a subcategory of LEO called Very Low Earth Orbit (VLEO).
Why is SpaceX doing this? And what are the implications of such decisions?
The biggest motivator behind this move is latency. At orbits this low, SpaceX satellites will have faster communications relay times than virtually any of their other competitors. And data speeds — as any internet user will tell you — are a critical component to the telecom business model.
But if lower orbits offer faster speeds, then why aren’t all telecom providers exploiting this space? The answer is orbital decay.
At these VLEO altitudes, the atmospheric drag on satellites is significantly greater. And without substantial propulsion engines to compensate at periodic intervals, these spacecraft are doomed to disintegrate in a fiery de-orbit within a matter of one to five years from their launch.
SpaceX’s Starlink satellite design features ion-propulsion engines which use Krypton emissions to make flight changes in orbit. But the supply of fuel onboard is limited. After that fuel supply is exhausted, those satellites will be unable to maintain their speed and altitude, and they will succumb to the principles of aerodynamics.
But why would SpaceX do this if these satellites are destined for an early death from the moment they’re launched? Surely, the market advantage in faster data speeds must be outweighed by the enormous cost of having to replace satellites so frequently, right?
For any ordinary telecom company, the answer would be yes. But SpaceX isn’t an ordinary telecom company. It is entering the telecom market with Starlink, but it is — first and foremost — a rocket launch company. As a result, SpaceX is able to launch its own satellites at a fraction of the cost that other non-rocket-launching telecom companies face.
SpaceX has created an innovative design for the Starlink satellites. Each satellite only weighs about 500 pounds, and 60 of them can be stacked into the payload bay of a single SpaceX Falcon 9 workhorse rocket.
SpaceX also reliably recovers its Falcon 9 first-stage boosters, so launch costs are considerably less than those for expendable rockets. The company has optimized the economics of Starlink launches to the extent that they likely cost a very small fraction of that which other telecom companies are forced to pay for comparable launches.
Additionally, SpaceX has publicly discussed that 95% of the components onboard the current (first) version of the Starlink satellites are “demisable.” That means those components will harmlessly vaporize in Earth’s atmosphere upon re-entry. The company has also stated it is aiming for 100% demisability with future iterations.
So it seems clear that SpaceX is planning to operate their telecom business on an entirely new model for satellite infrastructure: one that sacrifices spacecraft longevity for industry-leading communication speeds. Because SpaceX is in the unique position to handle their own satellite launches and deployments, this functionality will likely be a tremendous advantage for the company.
What does this mean for other satellite telecom competitors? In lowering satellite orbits, SpaceX has just raised the bar for the industry.
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About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a JD in Law and a Ph.D. in Hospitality/Business Management. He teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.