How Laser Communications Are Improving Satellites

The U.S. National Aeronautics and Space Administration (NASA) launched its Psyche spacecraft in October 2023 with the mission of reaching and studying a unique asteroid orbiting the Sun between Mars and Jupiter. While the craft is still traveling to its destination, it already is enabling incredible scientific progress.

That is because, as part of its mission, the Psyche spacecraft is testing new laser communications technology.

This new technology “encodes data in photons at near-infrared wavelengths (rather than radio waves) to communicate between a probe in deep space and Earth,” according to NASA. As a result, this method of communication can transfer much more data between the craft and Earth in a set amount of time than was previously possible. At one point during the demo, NASA reached maximum data transfer rates of 267 megabits per second when the craft was 19 million miles away from Earth, a rate comparable to broadband speeds.

At another point in the demo, Psyche was 110 million miles away from Earth and, predictably, laser communication speeds slowed down significantly due to the distance, reaching only about 25 megabits per second. However, this was still a huge win, because NASA’s goal was to prove that transmissions of at least 1 megabit per second were possible. This puts laser communication at anywhere from 10 to 100 times faster than the best radio frequency (RF) technology being used for similar purposes today.

This not only opens up new possibilities in deep-space communication, it also suggests that laser communication used closer to home, specifically between geostationary satellites (GEOs) and low Earth orbit satellites (LEOs), could soon become much faster and more reliable.

Laser communications and geostationary satellites

GEOs are satellites orbiting Earth’s equator at an altitude of about 22,000 miles. By the nature of their orbit, they appear stationary if you’re looking at them from Earth; in other words, they’re always over the same place. GEOs are able to cover large swaths of territory, so they’re widely used for telecommunications, navigation, and weather forecasting. GEOs predominantly rely on RF communication to transmit and receive data. However, thanks to NASA’s demos, there may now be a better way to operate these satellites.

Laser communication of the type demonstrated by NASA is capable of delivering significantly higher bandwidth than RF, with reduced size, weight, and power requirements on the satellite itself, said Francis Bennet, an astrophysics researcher at Australian National University.

That sentiment is echoed by John Degnan, a former NASA employee and independent technical consultant. “I believe lasers have a lot to offer in terms of size, cost, and bandwidth,” he said. “A 20-watt laser can transmit data at megabit rates per second to the farthest planets and at gigabit rates per second to our nearest neighbors.”

Those benefits become even more compelling when laser communications are applied to GEOs. Since GEOs are much closer to Earth than distant probes like Psyche, lasers should be able to help them transmit much more data at much faster speeds, both between the satellite and Earth—and to low Earth orbit satellites (LEOs) that are even closer to Earth.

“Since the distance between terminals in geostationary orbits is orders of magnitude smaller than interplanetary distances, much higher data rates can be accommodated between them with lower output powers and smaller ‘antennas’ (telescopes),” said Degnan.

GEO vs. LEO

This raises the question: Could GEOs armed with laser communications begin to outpace constellations of LEOs like Starlink?

LEO satellites orbit much closer to Earth than GEOs do, orbiting anywhere from about 100 miles to 1,200 miles above the surface. While they move much faster than GEOs, they also cover significantly less territory, so you need many more of them to cover an area. However, because they are so much lower to the ground, they are much better at low-latency applications, like transmitting voice calls or providing Internet service.

This is why LEOs are used to power Starlink, and LEOs are why Starlink can provide fast, high-quality, and reliable communications in typically poor coverage areas, like rural backwaters or active battlefields.

Instead of putting GEOs at odds with LEOs, advancements in laser communications will likely benefit LEOs, said Bennet. We could see longer-duration communication connections between GEOs and LEOs, he said, as well as an overall increase in the amount of data that LEO satellites can handle at any given time, thanks to lasers.

“[Lasers] can increase the capacity of data throughput of LEO satellites, which otherwise have to wait until they are overhead a ground station to downlink their data,” he said.

This is a particularly timely development. Thanks to advancements in instruments, satellites are now able to produce far more data than ever before. RF communications can struggle to accommodate this increased amount of data, said Bennet.

To that end, Starlink already has launched some satellites with optical inter-satellite links (OISLs), said Barry Evans, a professor of information systems engineering at the U.K.’s University of Surrey. But it’s not entirely clear if OISLs have yet been implemented in the entire Starlink constellation.

However, because of the clear speed and bandwidth benefits of laser communication, Evans expects they will be soon.

“For sure, in the next generation constellation, OISLs will be used,” Evans said.

He also expects laser communication to become increasingly prevalent, even in the gateways on Earth to satellites in orbit. The benefits are just too compelling, especially since narrow laser beams don’t have to deal with the same regulatory constraints that RF bands have, according to Evans.

Bennet also anticipates laser communication will continue to increase in speed and efficiency as the technology matures, leading to much higher downlink speeds for space probes and missions. That may end up in very high data rates similar to what is possible with fiber-optic links, he said.

In fact, work done by Degnan on laser communications suggests that gigabits or even terabits per second are potentially achievable using modestly powered lasers and reasonable telescope diameters. This type of technology, baked into both GEOs and LEOs, would help both do their specific jobs much better.

“Geostationary satellites and Starlink serve different purposes, so there is room in the market for both,” said Bennet.

As it turns out, maybe the sky really is the limit for satellite communication.

Logan Kugler is a freelance technology writer based in Tampa, Florida. He is a regular contributor to CACM and has written for nearly 100 major publications.