The T-Mobile/SpaceX service doesn’t care what brand of phone a user has, or which wireless network serves it. The emergency messages can reach any smartphone within range. But T-Mobile customers get a bonus: They’re able to send satellite text messages free of charge through the SpaceX satellites, to reassure their friends and relations.
In addition, owners of late-model Apple iPhones and the new Google Pixel 9 phone can send and receive text messages via satellite, using technologies that the two companies unveiled just weeks ago.
The SpaceX/T-Mobile system was successfully tested less than a month ago. The two companies hadn’t planned on activating the system yet. But with terrestrial cell sites in ruins, they got permission from the Federal Communications Commission to fire it up at once.
“We just thought that opening up access early, even though it’s not ready for commercial service, would allow us to actually help,” said John Saw, T-Mobile’s chief technology officer.
Standard satellite phones generally look like old-school walkie-talkies. How can a sleek little smartphone talk to a spacecraft?
“It’s a huge challenge,” said Saw. “These satellites are flying around in orbit about 200 miles away and they’re moving at 17,000 miles an hour.”
It’s all been made possible by a new generation of communications satellites, launched by SpaceX and a variety of other companies, including Apple’s satellite partner Globalstar, and AST SpaceMobile, which is working with Verizon and AT&T.
These companies are launching hundreds of satellites into low-earth orbit. Each has a big solar panel to provide power and large antennas capable of picking up the minuscule signals from earthbound smartphones.
“The satellites are powerful enough now that you don’t need a clunky big satellite phone,” said Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics. “You can just talk directly to the satellite.”
The satellites are basically cell towers in space. They monitor incoming phone signals on standard cellular frequencies, using software that can distinguish between individual phones.
The SpaceX system uses a network of lasers to let all its satellites relay data to each other. An incoming text message is sent by laser to the satellite nearest to its intended destination, then beamed to a ground station on earth, which sends it to the correct phone as a standard SMS message. A reply is sent to the satellite network, which uses a technology called “beam forming” to aim its radio signals at the correct phone.
The system doesn’t work perfectly. Apple and T-Mobile warn that there can be a significant delay in sending and receiving messages. Also, you’d better be outdoors. Like the signal from a GPS satellite, these transmissions can be blocked by buildings or trees because they are weaker than those issued by Earthbound towers.
McDowell said the satellites are also a nuisance to astronomers. Because they often reflect sunlight toward earth, they’ve begun to interfere with scientists’ ability to see into space using optical telescopes. And McDowell warned that the problem will get worse as more such satellites are launched.
Starlink already has about 6,400 satellites, with more than 200 of them capable of handling wireless phone traffic, and the company plans to launch thousands more. Rivals including Globalstar and AST are building similar satellite constellations and other countries like China are getting into the game.
McDowell said that the skies aren’t too crowded yet, but warned, “when it gets to be 30,000, 60,000, a hundred thousand satellites, then it’s going to be a problem.”
Alexander Wyglinski, professor of electrical and computer engineering at Worcester Polytechnic Institute, noted that any satellite-based phone system will also have to cope with “space weather,” bursts of cosmic radiation from the sun that could knock out portions of the network. There’ll need to be lots of redundancy in the system, and backup satellites ready for quick launch to replace any that go down. But with the falling cost of space launches, Wyglinski sees this as a manageable problem.
Apart from its use in disasters, satellite-to-cell systems can help with the nagging inability to hook up vast areas of Earth where it’s too costly to build terrestrial systems. T-Mobile estimates that half a million square miles of the US has no wireless service. Wyglinski thinks this is a job for space-based communications.
“You could continue building infrastructure and you’re still not going to capture all the gaps,” he said, “or you could go to another dimension, the third dimension.” Which is located about 200 miles straight up.
Hiawatha Bray can be reached at hiawatha.bray@globe.com. Follow him @GlobeTechLab.
