They skip mobile towers and cables: the phone or small dish talks straight to a satellite, which links it to the rest of the network.
Mobile phones need a tower nearby. Ships at sea, soldiers on a glacier and rescue teams after a cyclone often have none. Satellite links fill that gap in two common ways: small fixed dishes called VSATs (very small aperture terminals), and handheld satellite phones.
A VSAT is a small dish that sends and receives data through a geostationary satellite, usually to a larger hub station on the ground.
ISRO says GSAT-30 provides VSAT connectivity for ATMs and stock exchanges. GSAT-31 supports VSAT networks and cellular backhaul, meaning it can link a remote mobile tower to the main network. GSAT-31 also has a wide beam over the Arabian Sea, the Bay of Bengal and the Indian Ocean for communication at sea.
A satellite phone needs no tower at all. BSNL launched India's satellite phone service on 24 May 2017. The government said it would first go to agencies handling disasters, state police, the railways and border forces, and later to people on flights and ships. The service runs on Inmarsat's satellites.
India has also tested its own technology for this. GSAT-6 carries a 6 m S-band antenna that unfurls in space, with five spot beams over India. GSAT-6A, launched on 29 March 2018, was meant to test technologies for satellite-based mobile communication, including handheld ground terminals.
A newer idea is to talk to ordinary phones directly. SpaceX's Starlink Direct to Cell satellites act like cell towers in space and connect to normal 4G LTE phones. The first ones were launched in January 2024, and SpaceX said in a 2025 announcement that more than 400 were in orbit, with text messaging live in the United States and New Zealand.
It is hard to do. SpaceX notes that a phone has low antenna gain and low transmit power, and that the satellites move at tens of thousands of kilometres per hour relative to the user.
Pick a GSAT satellite and compare its almost fixed position with a low satellite that sweeps across the map in minutes. Track India's communication satellites
Why is talking to an ordinary phone from orbit so hard? Two numbers explain it: distance and speed.
Distance. A geostationary satellite is 35,786 km away. A phone's tiny antenna and low power cannot close a link that long on its own, which is why GSAT-6 needed a huge 6 m antenna in orbit to hear small terminals. A satellite flying near 550 km is about 65 times closer, and received power grows with the square of closeness: (35,786 / 550)² ≈ 4,200 times stronger for the same transmitter.
Speed. A low satellite moves fast. Circular orbital speed is v = √(GM / r). At 550 km, r = 6,378 + 550 = 6,928 km, so v = √(398,600 / 6,928) = √57.5 ≈ 7.59 km/s, about 27,000 km/h.
That speed shifts the radio frequency (the Doppler effect). The largest possible shift is Δf = f × v / c. For a 2 GHz signal: Δf = 2 × 10⁹ × 7,590 / 299,792,000 ≈ 50,600 Hz, or about 51 kHz. The true shift is smaller because only the part of the motion towards or away from the user counts, but it changes from positive to negative during every pass. A phone built for a fixed tower never expects this, so the satellite has to correct for it. That is one of the challenges SpaceX lists for Direct to Cell.
Very Small Aperture Terminal. It links places such as ATMs, stock exchanges and remote mobile towers to networks through a satellite.
To pick up weak signals from small ground terminals 35,786 km away; a larger antenna collects more of the signal.
Phones have low antenna gain and low transmit power, and low satellites move so fast that the signal's frequency shifts (Doppler).