Laser links connect Starlink satellites, reducing the need for ground stations.
SpaceX has begun launching Starlink satellites with laser links to help provide broadband coverage in polar regions. As SpaceX CEO Elon Musk wrote on Twitter on Sunday, these satellites “have laser links between the satellites, so no ground stations are needed over the poles.”
The laser links are included in 10 Starlink satellites just launched into polar orbits. The launch came two weeks after SpaceX received Federal Communications Commission approval to launch the 10 satellites into polar orbits at an altitude of 560km.
“All sats launched next year will have laser links,” Musk wrote in another tweet yesterday, indicating that the laser systems will become standard on Starlink satellites in 2022. For now, SpaceX only includes laser links on polar satellites. “Only our polar sats have lasers this year & are v0.9,” Musk wrote.
Alaskan residents will benefit from the polar satellites, SpaceX told the FCC in an application to change the orbit of some of its satellites in April 2020. The plan is to “ensure that all of the satellites in SpaceX’s system will provide the same low-latency services to all Americans, including those in places like Alaska that are served by satellites in polar orbits,” SpaceX said at the time. The satellites can serve both residential and US-government users “in otherwise impossible-to-reach polar areas,” SpaceX said.
Starlink satellites communicate with ground stations, of which about 20 have been deployed in the United States. A SpaceNews article today described how the laser links reduce the need for ground stations and provide other benefits:
Inter-satellite links allow satellites to transfer communications from one satellite to another, either in the same orbital plane or an adjacent plane. Such links allow operators to minimize the number of ground stations, since a ground station no longer needs to be in the same satellite footprint as user terminals, and extend coverage to remote areas where ground stations are not available. They can also decrease latency, since the number of hops between satellites and ground stations are reduced.
The 10 satellites were originally authorized by the FCC for altitudes in the 1,100-1,300km range. The FCC approval allowing SpaceX to cut the altitude in half will help reduce latency.
With polar orbits, also known as Sun-synchronous orbits, satellites “travel past Earth from north to south rather than from west to east, passing roughly over Earth’s poles,” as the European Space Agency explains.
“Space lasers have exciting potential.”
In December, during an interview with Ars’ Senior Space Editor Eric Berger, SpaceX President Gwynne Shotwell said that demonstrating laser communications in space was among the company’s most significant achievements in 2020.
SpaceX had revealed a few months earlier that it was testing space lasers for transferring data between satellites. Starlink engineers provided more detail in a Reddit AMA in November.
“The speed of light is faster in a vacuum than in fiber, so the space lasers have exciting potential for low latency links,” the Starlink team said on Reddit in response to a question about space-laser testing. “They will also allow us to serve users where the satellites can’t see a terrestrial gateway antenna—for example, over the ocean and in regions badly connected by fiber.”
Space lasers won’t play a significant role in Starlink soon, though. “We did have an exciting flight test earlier this year with prototype space lasers on two Starlink satellites that managed to transmit gigabytes of data,” the engineering team wrote. “But bringing down the cost of the space lasers and producing a lot of them fast is a tough problem that the team is still working on.”
SpaceX seeks FCC OK for more polar satellites.
In November 2020, SpaceX urged the FCC for an expedited approval “to facilitate deployment of 348 Starlink satellites into Sun-synchronous polar orbits at the lower altitude,” the FCC said in its decision to approve 10 satellites. The FCC approved only those 10 because it evaluates interference concerns raised by other satellite companies.
“We find that partial grant of ten satellites will facilitate the continued development and testing of SpaceX’s broadband service in high latitude geographic areas in the immediate term pending later action to address arguments in the record as to both grant of the modification as a whole and the full subset of polar orbit satellites,” the FCC order said.
Amazon’s Project Kuiper, Viasat, Kepler Communications, and Pacific Dataport urged the FCC to reject even the partial grant of 10 satellites because of the potential for increased interference with other non-geostationary satellite systems. But the FCC order said that SpaceX committed to “operate these satellites on a non-harmful interference basis concerning other licensed spectrum users until the Commission has ruled on its modification in full.” A battle between SpaceX and Amazon is brewing, with Musk accusing Amazon of trying “to hamstring Starlink today for an Amazon satellite system that is at best several years away from operation.”
