Space Lasers Come of Age: Optical Communications for Satellites Are Ready for Prime Time

The story of satellite communications is a tale of the search for more bandwidth. Physics defines the terrain of the search — communicating across the vast distances of space can only be accomplished using the electromagnetic spectrum, or EMS, where the higher the frequency (and the shorter the wavelength), the more data is encodable in the waveform. From S-band through C-band, to X-band and K-band, radio frequency, or RF, satellite communications have evolved from low frequency dial-up speeds to today’s multi-gigabit per second very high throughput satellites using wavelengths under one centimeter.

But the highest frequencies of all in the electromagnetic spectrum are in the visible light end of the spectrum, up to 10,000 times higher than even the highest frequency Ka-band RF. The technology has existed to encode data in visible light since the development of fiber optic communications in the ‘70s and ‘80s. By that time, lasers were already a mature technology, used in consumer electronic devices like laserdisc or CD players.

The use of lasers to communicate data from satellites — sometimes called free space optical communications, or FSOC, — has been a theoretical possibility for more than 40 years. The Japan Aerospace Exploration Agency demonstrated the technology in 1995, successfully achieving 1 megabit per second data download speeds from its engineering test satellite KIKU-6, to a ground station in Tokyo.

Today, a dozen or so companies, from startups to aerospace giants and major defense contractors are developing and selling free space optical technology, either to communicate with ground stations or between satellites in orbit or other spacecraft, with speeds up to 100 gigabits a second. Several test or demonstration projects are launching this year and if they are successful, the next two to four years could finally see the start of broad-scale deployment of FSOC technology in military and commercial constellations.

So, if the story of satellite communications is truly the tale of a search for greater bandwidth, perhaps the most pertinent question to ask about the use of FSOC is: What took so long?

A New Technological Paradigm

One factor which caused delays in deploying the technology, according to Thomas Wood, senior director for Optical Communications and Networking for defense and government contractor CACI, is that laser communications are a completely new paradigm. “When you go from Ku-[band] to Ka-, you may need to change the antenna, but it's basically the same technology. It's an incremental change. The technologies for laser communications are quite different — instead of an antenna, we have a telescope; instead of a gallium nitride transistor-based amplifier, we have a doped fiber amplifier.”

That paradigm shift made operators nervous about adoption, explains Wood. “In the beginning, there was a lot of concern about betting on a relatively unproven technology for missions [in space] where you couldn't go out and fix it, if it didn’t work.”

The engineering challenges are significant, he acknowledges. Satellites in orbit are moving at 17,000 mph in Low-Earth Orbit (LEO), and laser communications employ much narrower beams than RF, “That means that the precision of the pointing has to be much higher. A great deal of the technology development has gone into building the systems for precision pointing, and I would say that's a solved problem now,” Wood says

And those solutions will soon be visible to everyone. Wood tells Via Satellite that over the past couple of years, CACI had delivered components to NASA for three in-flight FSOC systems, slated to launch within the next two years. One of which, the ILLUMA-T system will be placed aboard the International Space Station next year. ILLUMA-T will make ISS the first orbital user of NASA’s Laser Communications Relay Demonstration, a Geostationary Orbit (GEO) satellite launched last year that can receive optical communications from other satellites and spacecraft and beam them down to earth.

Then there’s the Orion Artemis II Optical Communications System, or O2O, scheduled to be launched in 2023 aboard the first crewed flight of the Orion space vehicle, which NASA plans to take astronauts to the Moon by the end of the decade. O2O will demonstrate the capability to transmit broadband data, from spaceships in orbit around the Moon or even, potentially, Mars.

“You’ve probably seen the staticky, blurry, jerky, black and white video from the Apollo 11 moon landing,” notes Wood. “Well, the next time they go back to the moon, NASA will have a better story to tell — in HD video.”

NASA’s commitment to FSOC will drive broader commercial and government adoption of the technology, argues Wood, saying it was a product of the hard work of engineers and technologists. Over 20 years, “we have gradually, through a wide variety of demonstrations and a lot of good engineering work, improved the technology and shown that we've burned down the risk to the point where people are willing to bet on it,” he says.

CACI is betting on it heavily. In December, the company completed its acquisition of SA Photonics, a company that Wood says was strongly positioned to address the mass market for optical communications that will be created by the LEO mega-constellations. And this isn’t the first investment that the $6 billion a year contracting giant has made in the field. Wood’s own career at CACI began when his employer, LGS Innovations, a former Bell Labs spinoff specialized in optical and other high security communications technology for national security agencies, was bought three years ago.

And CACI is far from alone. Projections from satellite consulting firm NSR say that the market for laser communication terminals for satellites will be worth $3 billion over the next ten years.

Market projections notwithstanding, space is a very unforgiving environment and the technical challenges remain considerable, says Blue Marble Communications President and CEO Neal Nicholson. “Over the recent past there’s been not only challenges in the [FSOC] technology itself, but it’s also been hampered by spacecraft failures, launch delays, and other assorted issues,” he says, warning against any Pollyanna-ish projections of guaranteed success.

Those challenges are demonstrated by Blue Marble’s own history, Nicholson says. The company developed radiation tolerant optical modems suitable for space deployment and capable of 100-200 gigabits per second speeds, but couldn’t find anyone with the capability to manufacture the front end of the terminal, which receives the optically encoded data.

“Our challenge was finding a suitable partner that could provide an affordable and capable optical head,” he says. “Eventually, BMC decided to develop our own front end,” at the beginning of 2021, and will be delivering fully qualified optical terminals later this year, Nicholson says.

In the industry as a whole, he adds, “We’re very close to having some successful demos with acceptable data rates and reliable pointing, acquisition and tracking.”

Bandwidth Demand Drives Deployment

Another factor that slowed adoption of FSOC, says Barry Matsumori, CEO of BridgeComm, was the question of demand. “RF works fine for single digit or even tens of gigabits per second,” Matsumori notes, and it was only recently that demand had begun to outpace the bandwidth that RF could provide.

“The demand now is not for just one gigabit per second, not 10 gigabits per second, but tens if not hundreds of gigabits per second. And it’s growing exponentially. The only way to achieve that is by starting to use optical communications or laser communications to augment or to complement RF communications,” he says.

Matsumori points out that FSOC used the same wavelength as fiber optics, meaning they could adopt technologies already tried and tested over cable. “We reuse the lasers, we reuse the amplifiers, we are reusing lots of equipment that has already been amortized in the fiber optic world.” But that overlap also meant FSOC could look to adapt new technologies developed to maximize bandwidth over fiber optic cable.

“Now, the real question is, can you take 100 gigabits per second, and then start doing wavelength-division multiple-access on a signal to reach 10 times [that data rate], which is a terabit [per second,]” he asks.

“The roadmap says a terabit [per second] is not that far away,” Matsumori concludes.

That huge growth in bandwidth will be needed to service new Earth observation constellations coming on line over the next couple of years, points out Tina Ghataore, CCO of Germany-based Mynaric, and president of Mynaric USA, its California subsidiary.

“The sheer size of the data files created by new Earth observation technologies like synthetic aperture radar, means the raw data simply can’t be downloaded using RF, '' Ghataore says. “That’s where optical [communications] really gives you that value in being able to not just send in the onboard processed information, but the raw data down in a very secure way to the ground.”

Mynaric, which was founded in 2009 as a spin-off company of the German Aerospace Center — a government research institution — sees the FSOC revolution as about far more than just bandwidth, according to CEO Bulent Altan.

It’s about the power of the network, Altan argues. Optical inter-satellite links, or OISL — that part of optical communications which deals exclusively with communications between satellites — can impart to the new LEO and Medium-Earth Orbit (MEO) constellations the same resilience and connectivity enjoyed by the terrestrial internet.

OISL and smart routing tools — AI algorithms that design the most efficient path for data packets — combine to make satellite constellations into self-governing networks, explains Altan. Rather than bringing data to the ground immediately, and paying terrestrial network providers to move it to the end user, the smart mesh will move data around in orbit and bring it to Earth via the ground station closest to the end user — using OISL technology to maximize network efficiency.

“What optical communications does is it takes these singular satellites in orbit and makes them into a coherent network just like the internet,” he says.

The Economics of Scale and the Absence of Standards

But realizing this vision for the new LEO mega-constellations, points out Ghataore, means being able to produce FSOC terminals at comparatively low cost — in “an affordable, scalable manner.”

But there's one huge problem as FSOC technology scales up to support mega-constellations, warns Greg Kuperman, a program manager in the Defense Advanced Research Projects Agency (DARPA) Strategic Technology Office.

“All of these constellations, each of them is going to be speaking a different language.” Imagine if there was no IEEE 802.11 standard for Wi-Fi, and every equipment manufacturer just went to market with their own technology. That’s the no-kidding situation in the optical communications market, says Kuperman.

Visible light is not regulated or licensed, and the glacial pace at which standards development has progressed means that “It's faster and easier right now for a company like SpaceX or Amazon to go build their own [equipment to their own standard],” Kuperman says.

But because the technical requirements for optical communications equipment are so severe, the investment involved in rolling out OISL capability is considerable, and it represents sunk costs into that technology. “This high degree of customization makes it so that when somebody decides on a particular standard, they're going to go put an investment to roll out… It'll be fixed, it'll be very hard to change,” says Kuperman.

But the U.S. government needs to be able to utilize capabilities on all of the proliferating networks, to maximize the agility and resilience of its satellite communications, he adds, and Balkanization is a danger: “If everyone is speaking their own language …using their own waveforms, their own coding protocols … we will have these islands of connectivity” disconnected from each other.”

To head off that orbital tower of Babel, the program he runs at DARPA, the Space-Based Adaptive Communications Node, or Space-BACN, aims not to impose a standard, but to produce a terminal that can receive data from many different systems. “If everyone is speaking their own language, I want to be multilingual,” he says.

If it is to achieve the required ubiquity, Kuperman says, the Space-BACN terminal must also meet three “100” benchmarks — it must be capable of 100 gigabits per second data throughput, it must use less than 100 watts of power and it must cost less than $100,000.

The end game is about connectivity, he says, “I want to be able to link into that global [satellite] network … the way I do into AT&T or Verizon infrastructure [on the terrestrial side]… It's kind of like plumbing, no one wants to think about it, it just needs to be there.” VS