Experts cite challenges and opportunities for optical communications
Satellite ground segment providers tend to be skeptical of ground-based optical communications.
They don’t doubt the utility of optical intersatellite links.
They simply question how quickly optical terminals will be adopted by enterprise customers to link satellites in low-Earth orbit with the ground.
“Personally, I don’t think optical to low Earth orbit is really going to go,” said Rolf Skatteboe, president and CEO of Kongsberg Satellite Systems, the Norwegian company that established the first commercial ground station in Greece in 2020. “There will be a lot of satellite-to-satellite links. But more interesting is optical to moon and beyond.”
Skatteboe made the comment Sept. 15 during a World Satellite Business Week panel in Paris, where he noted KSAT was operating the first commercial optical ground terminal.
Swedish Space Corp. is “skeptical as well” regarding the speed of optical communications adoption, said fellow panelist Nick Priborsky, SSC Satellite Management Services president. “Nevertheless, it’s also important to get that experience under your belt.”
SSC announced plans later that day to establish its first optical ground station in Western Australia.
Why are companies building optical ground stations if they are dubious about the technology’s near-term prospects? In part, because government agencies are picking up the tab.
SSC’s optical ground terminal was funded by the European Space Agency. In the United States, the Space Force’s Space Development Agency is spending billions of dollars on satellites equipped with optical terminals to communicate with other spacecraft as well as airborne and ground terminals.
For government agencies, part of the appeal is security. Optical signals travel in a narrow beam of light, making them harder to intercept or jam than radio frequency signals.
“You may send the RF beam to the satellite you intend to, but behind it in the shadow there is another” satellite, said Shantanu Gupta, Aerospace Corp. chief engineer for optical communications. “Interference will happen because the [RF] beam is 1,000 to 10,000 times broader than the optical beam.”
Optical links also can speed up transmission of the massive amounts of Earth observation data obtained by optical and synthetic aperture radar satellites from satellite to satellite and from space to the ground.
“You’re at a point where the sensors can generate a lot more data,” Gupta said. “If you had fat pipes to bring it down with low latency, that would be very useful because still most of the processing and computing power is on the ground.”
Overall, optical communications is “a great technology for enabling high-data-rate connections and providing resiliency between platforms,” said Julee Pandya, Lockheed Martin senior manager for communications and networking technologies. Like RF communications, optical technologies are tools that can be applied “to maximize their benefit for a particular customer need and application,” Pandya said in an interview.
Lockheed Martin is producing satellites for the Space Development Agency equipped with optical terminals provided by Tesat-Spacecom, an Airbus U.S. subsidiary.
AT WHAT COST?
Skeptics don’t doubt whether optical signals can transmit data to and from space.
The Japanese space agency JAXA established an optical link in 2006 between a ground station in Tokyo and its Optical Inter-Orbit Engineering Test Satellite in low-Earth orbit. NASA’s Lunar Laser Communications Demonstration on the Lunar Atmosphere and Dust Environment Explorer satellite sent high-definition video from the ground to lunar orbit in 2013.
Nor do people question the value of optical intersatellite links.
“Generally speaking for intersatellite links, almost everybody is thinking of optical,” Gupta said in an interview. “It’s almost getting to where it’s mature.”
The Pentagon’s Space Development Agency, for example, plans to launch hundreds of Transport Layer satellites with optical crosslinks to transmit imagery and data around the world, plus RF and optical terminals to send them to the ground.
“Once you get data onto the Transport Layer, I can move it to whatever weapon system it needs to go to, I can fuse the data,” SDA Director Derek Tournear said in October at the MilSat Symposium in Mountain View, California.
SDA’s vote of confidence in optical technology coupled with the agency’s purchasing power is helping drive down the cost of optical terminals.
Early optical communications demonstrations were performed by government agencies flying bespoke terminals. In recent years, companies have slashed the cost of optical terminals and set up mass manufacturing to supply satellite constellations.
“The challenge is making it so that the terminals are producible at an economic cost and schedule that systems can afford,” said David Czajkowski, CEO, director and co-founder of Space Micro, a firm acquired earlier this year by Voyager Space. Space Micro is under contract to supply optical terminals to the Space Force Space Systems Command.
PIERCING EARTH’S ATMOSPHERE
While companies are making steady progress on the economic front, ground segment providers point out other challenges.
Clouds and fog block optical signals. And Earth’s atmosphere distorts light waves, causing fluctuations in their intensity.
Getting optical links “set up and getting them to work reliably when nothing is moving is really challenging,” Andrew Ivers, president of Communications and Power Industries, an electronic component manufacturer, said during the World Satellite Business Week panel. “Getting them to work in a scintillating atmosphere, when everything is moving around a little bit and you have even mild weather, can be a huge issue.”
If that issue can be solved, optical technology “has a great, great home in the satellite industry,” added fellow panelist Paul Gaske, Hughes Network Systems executive vice president and general manager. “If you look at the amount of capacity that you need to get to a satellite in the [high-throughput satellite] world, we’ll put in 20 gateways or 200 gateways of smaller size. We’re doing that because we can’t get enough bits in a single stream. But if you could get an optical link to work, that would be great.”
To lessen the impact of weather, organizations seek sunny locations or mountaintops for optical ground stations. Unfortunately, those sites don’t always provide the necessary terrestrial infrastructure.
“I need internet connections to my gateway,” Kartik Seshadri, vice president of Hughes Network Systems International Division, said in an interview. “I need good diverse, highly available fiber to the internet.”
To clear that hurdle, companies are establishing geographically dispersed ground station networks.
“It comes down to diversification,” Andrew Csizmar, Honeywell senior director of small satellites, said at World Satellite Business Week. “If you get enough ground stations, you will get the throughput that you need, but it’s going to be on a global basis. Connectivity then is about how you get that backhaul back to the users.”
Honeywell is working with Skyloom to provide optical intersatellite links for Space Development Agency satellites being built by York Space Systems.
Companies are addressing the distortion caused by Earth’s atmosphere with technology.
Atmospheric air currents can carry smoke or water vapor that interferes with optical waves.
To neutralize atmospheric turbulence, wavefront sensors determine the atmosphere’s impact on a light beam and employ fast-steering or deformable mirrors to compensate for the disruption. Ground-based observatories employ similar technologies to improve the quality of astronautical images.
“It’s a control loop,” Gupta said. “You sense it and correct it with adaptive optics.”
Looking to the future, Lockheed Martin is investigating nonmechanical techniques to address atmospheric turbulence.
“We want to move away from things that can be hard to manufacture and integrate,” Pandya said. “A nonmechanical solution is envisioned for the future to improve the overall reliability of some of these systems as well as reduce size, weight and power.”
This article originally appeared in the November 2022 issue of SpaceNews magazine under the title “Walking a Narrow Beam: Laser links are great for satellite relay, but challenges abound for taking it to ground.”