Space Laser Based Satellite Communications System Tested

With some 5,000 satellites already orbiting the Earth, and a possible 100,000 expected to be launched by the end of the decade, it’s getting awfully crowded in low-earth orbit. And given the limited radio and microwave frequency spectrum (ranging from 1 to 40 gigahertz) available for satellite communications, satellite-to-Earth connections are facing an ever-narrowing data bottleneck.

Which, in part, is why astronomers have stepped forward with an alternative. Researchers at the University of Western Australia’s (UWA) International Centre for Radio Astronomy Research in Perth are building a network of infrared laser base stations—two ground stations and a mobile station, dubbed the TeraNet project—whose 200 THz waves offer the potential of orders of magnitude more data capacity than radio waves. Last month, the team reports they successfully captured the signals sent from a German low Earth orbit satellite, a critical first step in establishing next-generation space communications.

The researchers built TeraNet with off-the-shelf tech wherever possible, says Sascha Schediwy, research group leader in astrophotonics at UWA’s International Centre. “We’re validating that you can build these complex ground stations on a modest budget. You don’t need to be a national space agency like NASA to get into free-space optical communications,” he says.

For example, Schediwy says, the core component of each ground station is a commercially sourced, larger version of an optical telescope anyone might use for stargazing. Once encoded with data, the beam is then transmitted through the telescope set to target a specific satellite as it passes over the ground station—similar to how laser technology is used to transmit data through optical fiber across the internet.

Conversely, when a satellite sends data to the ground station, a similar laser system on the satellite directs the beam of data down to the ground station’s telescope. The ground station’s optical terminal filters and processes the signal, and passes it on to the optical modem, which converts the optical signal into digital data.

Of course under overcast skies—or during rainy or other adverse weather conditions—a laser data link between a ground station and an orbiting satellite is going to be choppy and unreliable at best. So the researchers spread out their ground stations geographically, so that if one station is clouded out, a satellite can send its data to another station that’s under clear skies.

Demoing the Infrared Downlink

To demonstrate the technology, the team used a ground station (with a 70-centimeter telescope) and a mobile station (with a 43-cm scope)—in this round of tests in data-receiving mode only.

A prototype network of two telescopes—one mobile and one based at an observatory at the University of Western Australia in Perth—tests technologies being developed for laser-based satellite communications. Danail Obreschkow/International Space Centre

“The tricky part in moving outside of fiber into free space, is that the turbulence in the atmosphere perturbs the signal and changes the waveform hundreds of times a second,” says Schediwy. “So, you need an optical system terminal integrated with the telescope consisting of mirrors, splitters, cameras and detectors to correct for these atmospheric events.”

The mobile station, built on the back of a custom-built Jeep, uses compasses, GPS, and an inertial navigation unit to determine the truck’s position and orientation. Looking up the target satellite’s orbit and fly-by time online, the algorithm points the telescope in the expected direction of the satellite as it arrives over the horizon.

“When the camera integrated with the telescope receives the signal, it maintains the telescope’s focus on the signal until the optical systems take over to keep the moving beam centered for receiving the data, which is then processed and sent on to the modem for digitization,” says Schediwy.

Unlike other attempts at establishing mobile ground stations around the world, which can take several hours or even a couple of days to set up, according to Schediwy, he says the entire procedure for the TeraNet mobile station takes about 15 minutes, day or night.

The satellite data is transmitted on a 1,550-nanometer infrared laser and, according to Schediwy, delivered data throughput measured so far only in megabits per second. “But with the technology proven,” he says. “We will now upgrade the equipment and work towards our roadmap target of 1 terabit-[per]-second bandwidth by the end of 2026.”

He says they’re working with colleagues at the Australian National University in Canberra and other organizations to establish larger networks of ground stations in Australia and New Zealand.

“If we can all make our ground stations compatible,” says Schediwy, “then satellite operators can be assured that they will have secure download capabilities in Europe, in Australia and elsewhere, as their satellites orbit the world.”