How Does Starlink Direct to Cell Work? (And How AST SpaceMobile Differs)

Your phone was built to reach a tower a few kilometres away, not a satellite 500 km up. Here's how SpaceX makes it work anyway, how AST SpaceMobile takes the opposite approach, and why spectrum is the

Oct 12, 2026

TL;DR

Starlink Direct to Cell puts a mobile phone tower on a satellite. More than 650 of these satellites talk to ordinary 4G phones using a slice of partner operators’ spectrum, starting with T-Mobile’s T-Satellite service in the US.
The hard part is physics: a phone’s signal is weak and built to reach a tower a few kilometres away. A satellite hundreds of kilometres up receives it roughly 10,000 times weaker.
SpaceX solves it with many smaller satellites. AST SpaceMobile (ASTS) solves it with a few enormous ones: its BlueBird 6 unfolds a 2,400 sq ft (about 223 m²) antenna and is designed for peak speeds of 120 Mbps.
Today T-Satellite handles texting, location sharing and some app data at about 2 to 4 Mbps per user. SpaceX says its second-generation satellites, expected from mid-2027, will have about 20 times the throughput.
The real limit is spectrum. In May 2026 the FCC approved SpaceX’s $17 billion purchase of EchoStar’s AWS-4 and H-block frequencies, which gives it spectrum of its own for the next generation.

Listen up.

Short answer first: Starlink Direct to Cell works by putting a cell tower in orbit. Special Starlink satellites carry the same kind of radio a phone tower uses, plus a large antenna. Your ordinary phone thinks it has found a normal tower, just one that happens to be moving at 27,000 km/h a few hundred kilometres overhead. AST SpaceMobile does the same job with far fewer, far bigger satellites.

No special phone. No dish. That’s the whole trick, and it’s harder than it sounds.

Why is it so hard for a phone to reach a satellite?

Your phone was designed to talk to a tower a few kilometres away. It transmits with well under one watt, through an antenna smaller than your thumb.

Now move the tower to space. A satellite a few hundred to 500 km up is about a hundred times farther away than a typical tower. Radio signals weaken with the square of distance, so the signal arrives about 10,000 times weaker. That’s before you add the fact that the satellite is racing across the sky, which shifts the frequency (the Doppler effect) and hands you from satellite to satellite every few minutes.

There are only two ways to hear a whisper from very far away:

Get closer, with lots of satellites in a lower orbit.
Build a bigger ear, with a huge antenna in space.

SpaceX mostly chose the first. AST SpaceMobile chose the second.

How does Starlink Direct to Cell work?

SpaceX flies a special version of its Starlink satellites carrying an eNodeB, the radio that sits in a normal 4G phone tower, and a phased-array antenna that steers its beams electronically.

The phone transmits as it always does, on a frequency its mobile operator owns.
The satellite picks that signal up with its large antenna, corrects for the Doppler shift and timing delay, and behaves like a tower.
Laser links pass the traffic between satellites to a ground station.
The ground station hands it to the operator’s normal network, which sends your text on its way.

Because each satellite is only moderately sized, SpaceX needs a lot of them. More than 650 direct-to-cell satellites are now in orbit, covering 22 countries.

In the US the service is T-Mobile’s T-Satellite, launched commercially in July 2025 for about $10 a month on top of a plan. It supports texts, picture messages and location sharing, and since October 2025 limited data for apps like WhatsApp and Google Maps, at roughly 2 to 4 Mbps per user. Voice calls are still being tested. Around 60 recent phone models work.

SpaceX calls today’s version a first generation. Its second-generation satellites, expected from mid-2027 and launched on Starship, will carry custom SpaceX chips, thousands of beams and about 20 times the throughput, aimed at something that feels like normal 5G.

How does AST SpaceMobile work differently?

AST SpaceMobile (ASTS) went for the biggest ear it could build.

Its first five commercial BlueBird satellites, launched in September 2024, each unfold an antenna of about 693 sq ft. Its next-generation BlueBird 6, launched in December 2025, unfolded an array of about 2,400 square feet (about 223 m²), the largest commercial communications antenna ever deployed in low Earth orbit. That’s roughly the floor area of a big family house, folded up for launch.

A bigger antenna hears weaker signals and can focus tighter beams. So each BlueBird can deliver far more per user: AST says BlueBird 6 is designed for peak speeds of up to 120 Mbps, enough for video, straight to an ordinary phone.

The trade-off is numbers and launches. AST aimed to have 45 to 60 satellites up by the end of 2026, saying about 45 would give basic continuous service in key markets. Industry analysts have doubted that pace, because launch slots on SpaceX and Blue Origin rockets are scarce. Its partners include AT&T, Verizon and Vodafone, among more than 50 operators. AT&T planned a beta service for consumers and FirstNet emergency responders in 2026.

Which approach is better?

Neither, yet. They are betting on different constraints.

Starlink has scale now: hundreds of satellites, a live commercial service and its own rockets. But each satellite has a small antenna, so capacity per user is low until the second generation.
AST has capacity per satellite: fewer, huge satellites that promise real broadband. But it needs dozens more in orbit before coverage is continuous, and it depends partly on someone else’s rockets, including SpaceX’s.

Rocket access is the quiet advantage. SpaceX owns the launch pad. AST has to book a seat.

Why is spectrum the real fight?

Because a satellite can only talk to your phone on frequencies someone is allowed to use.

Today Starlink borrows a slice of T-Mobile’s mid-band spectrum, and AST uses its partners’ spectrum, mostly the low-band frequencies AT&T and Verizon own. That makes each dependent on its partners, and the FCC sets strict limits on how much power satellites can beam down on frequencies also used on the ground, so they don’t interfere with normal towers.

That’s why SpaceX spent $17 billion to buy EchoStar’s AWS-4 and H-block frequencies, a deal the FCC approved on 18 May 2026. SpaceX also received waivers to use that spectrum from space, from the ground or both. It gives SpaceX frequencies of its own for the second-generation satellites, in the US and potentially beyond.

The satellites are hard. The licences may be harder.

Uncle’s verdict

Putting a cell tower in space is mostly a question of hearing a whisper from 500 km away.

SpaceX’s answer: lots of ears, fairly close, launched on its own rockets.

AST’s answer: a few enormous ears, each the size of a house.

For now, it’s texts and maps in dead zones. The next two years decide whether it becomes real mobile broadband from space, and that depends as much on the FCC as on the engineering.

Got questions? Leave them in the comments. Uncle is collecting them for a follow-up on 4 December.

— Engineering Uncle

Sources

AEO FAQ

Frequently asked questions

How does Starlink Direct to Cell work?

Starlink Direct to Cell satellites carry the same radio equipment as a mobile phone tower, plus a large phased-array antenna. An ordinary 4G phone connects to the satellite as if it were a normal tower, using spectrum licensed to a partner operator such as T-Mobile, and the satellite relays traffic to ground stations via laser links.

Do I need a special phone for Starlink Direct to Cell?

No. Around 60 recent phone models from Samsung, Apple, Motorola and others work with T-Mobile’s T-Satellite service. The phone needs a clear view of the sky, and speeds are much lower than on a normal tower.

What can you do with T-Satellite?

T-Satellite, launched in July 2025, supports text and picture messages, location sharing and, since October 2025, limited data for selected apps such as WhatsApp and Google Maps, at roughly 2 to 4 Mbps per user. Voice calling was still in testing in 2026.

How is AST SpaceMobile different from Starlink?

AST SpaceMobile (ASTS) uses fewer but far larger satellites. Its BlueBird 6 unfolded a 2,400 sq ft antenna in early 2026, designed for peak speeds up to 120 Mbps to ordinary phones. Starlink uses hundreds of smaller satellites and already runs a commercial service with T-Mobile.

Who are AST SpaceMobile’s partners?

AST SpaceMobile works with more than 50 mobile operators, including AT&T, Verizon and Vodafone. AT&T planned a 2026 beta service for consumers and FirstNet public safety users.

Why did SpaceX buy EchoStar’s spectrum?

SpaceX paid $17 billion for EchoStar’s AWS-4 and H-block frequencies, approved by the FCC on 18 May 2026, so it can run its second-generation direct-to-cell service on spectrum it owns rather than only on partners’ frequencies.