Satellite networks

How networks in orbit work, from scratch: why we put radios in space, the orbits they fly, what each orbit costs in latency, how a link runs from a dish to a gateway, what is inside a satellite and a user terminal, how constellations hand you from one satellite to the next and relay traffic with lasers, the main systems as of late 2026, satellite-to-phone service, how GPS finds you, rain fade, debris and regulation. Radio basics (frequency, antennas, modulation, link budgets) are in Radio; phones on the ground are in Cellular; what happens to your packets once they land is in Autonomous systems & BGP.

Why satellites

A satellite is a radio tower placed very high up. The higher a tower, the more of the Earth it can see: a cell tower covers a few kilometers, a satellite 550 km up can serve a circle about 2,000 km across, and one at 35,786 km sees about 40% of the planet's surface. Cables and towers have to be built where the users are; a satellite serves anyone who can see it.

The costs: a beam's capacity is shared by everyone under it, so satellites serve sparse areas better than cities; distance adds delay; rain weakens high frequencies; terminals need a clear view of the sky; and every satellite has to be built, launched and replaced.

Orbits

Nothing holds a satellite up. It is falling, but moving sideways so fast that the ground curves away beneath it as fast as it falls. The lower the orbit, the stronger gravity and the faster it must go: about 7.6 km/s at 550 km (a lap in 95 minutes), about 3.1 km/s at 35,786 km, where one lap takes exactly as long as the Earth takes to turn once. A satellite there, above the equator, hangs over one spot: it is geostationary.

• Inclination is the tilt of an orbit against the equator. Polar orbits (≈ 90°) pass over every latitude; GEO must be at 0°, so it sits low on the horizon at high latitudes and is out of sight near the poles.
• A Molniya orbit is tilted 63.4°, the one angle at which the Earth's bulge doesn't drag the high point around the orbit, and spends most of each lap near that high point. Three satellites take turns to cover the far north, where GEO is too low to use.
• A sun-synchronous orbit (polar LEO, ≈ 500–800 km) crosses each latitude at the same local time every day, which Earth-observation satellites use for consistent lighting.

The period follows from Kepler's third law, with a the distance from the Earth's center:

T = 2π × √(a³ / μ)        μ = 398,600 km³/s² (Earth)
 
LEO at 550 km:  a = 6,371 + 550 = 6,921 km   → T ≈ 5,730 s ≈ 95.5 min
GEO:            a = 42,164 km                → T ≈ 86,164 s = 23 h 56 min 4 s
                (one sidereal day: one turn of the Earth against the stars)

Latency: the speed of light, worked out

Radio travels at the speed of light, c ≈ 299,792 km/s, so distance is delay. In a simple bent-pipe system (the satellite only relays) a request goes up to the satellite and down to a gateway, and the reply comes back the same way: four trips between the ground and the satellite.

GEO (35,786 km straight up)
  one trip            35,786 km ÷ 299,792 km/s ≈ 119 ms
  request + reply     4 × 119 ms ≈ 477 ms            best case
  real slant paths    ≈ 37,000–40,000 km each way → ≈ 500–540 ms
  + modems, queues, the path from the gateway to the server
  typical round trip  ≈ 600 ms or more
 
LEO (550 km)
  one trip            550 km ÷ 299,792 km/s ≈ 1.8 ms
  request + reply     4 × 1.8 ms ≈ 7.3 ms            best case
  satellite low in the sky (25° up): ≈ 1,100 km each way → ≈ 15 ms
  + scheduling, the gateway, the POP, the server's distance
  typical round trip  ≈ 20–50 ms to a nearby server

GEO's half second is physics: no upgrade removes it. Web pages feel sluggish, video calls get awkward pauses (ITU-T G.114 treats one-way delays under about 150 ms as fine for most voice; GEO is about 250 ms one way), and competitive online games are impractical. LEO latency is close to cable or DSL, which is why consumer satellite broadband has moved to LEO. How round-trip time limits throughput is in Fundamentals.

Anatomy of a satellite link

Every satellite internet connection has the same parts:

• User terminal: the dish or flat panel, plus a modem and usually a Wi-Fi router.
• User link: the radio link between the terminal and the satellite.
• Satellite: receives, maybe processes, and retransmits.
• Feeder link: the radio link between the satellite and a gateway (also ground station or teleport), a site with large dishes connected to fiber.
• POP (point of presence): a data center where the operator's network meets the rest of the internet.

Uplink means toward the satellite, downlink toward the ground. Each direction uses a different frequency so the satellite's powerful transmitter doesn't drown out the faint signal it is receiving.

Which band (range of radio frequencies) a link uses decides its antenna size, capacity and weather sensitivity. Higher frequencies carry more data and allow narrower beams from smaller antennas, but rain absorbs them. The letter names come from radar history; the satellite industry uses them loosely, so a "Ku-band" TV downlink at 11 GHz sits below the formal 12 GHz edge.

How to size a link (transmit power, antenna gain, path loss, noise) is in Radio: link budgets.

Bent pipe vs regenerative payloads

The payload is the part of the satellite that does the mission; for communications, the radios. There are two designs.

A transponder is one receive-convert-amplify chain in a bent-pipe payload, classically 36 to 72 MHz wide; TV channels and capacity were long sold by the transponder. Software-defined payloads blur the line: their beams, frequencies and power can be reassigned in orbit.

Inside a satellite

A satellite has two halves: the bus, the platform that keeps it alive and pointed, and the payload.

Scale varies a lot: a large GEO satellite weighs several thousand kilograms and is designed to last about 15 years; mass-produced LEO constellation satellites weigh from about 150 kg to over 1,000 kg and last roughly 5 to 7 years, then burn up in the atmosphere.

User terminals

The terminal has to point a narrow beam at a satellite. GEO satellites stay put, so a fixed parabolic dish works: a curved mirror that focuses the signal onto a feed horn. LEO satellites cross the sky in minutes, so the terminal has to track them.

A phased array steers by constructive interference: if each element transmits a little later than its neighbor, the waves line up along a tilted front.

delay between neighbors    τ = d × sin θ / c
phase between neighbors    Δφ = 2π × d × sin θ / λ
 
d: element spacing, θ: beam angle from straight up, λ: wavelength
elements sit about λ/2 apart, or false beams (grating lobes) appear
Ku band at 12 GHz: λ = c / f = 25 mm, so spacing ≈ 12.5 mm

All terminals need a clear view of the sky: trees, roofs and walls block these frequencies. A phased array also loses gain when it steers far from straight up, which is one reason systems avoid satellites low on the horizon.

Constellations and handoffs

A LEO satellite at 550 km, used only when it is at least 25° above the horizon, serves a circle about 1,900 km across and passes over in at most about 4 to 5 minutes. Continuous coverage everywhere takes hundreds of satellites, and enough capacity for millions of users takes thousands.

• A constellation is organized in orbital planes (rings of satellites sharing one orbit's tilt) and shells (sets of planes at one altitude and inclination).
• Planes tilted about 53° concentrate satellites over the mid-latitudes where most people live; polar planes cover the poles.
• The minimum elevation angle is a trade: lower means fewer satellites needed, but longer, more obstructed paths.

Because satellites keep moving, every terminal and gateway is handed from one satellite to the next, many times an hour.

The beams of the terminal and of the satellite both move, so a central scheduler plans who talks to whom. Measurements of Starlink show a globally synchronized reconfiguration every 15 seconds, with brief latency spikes at each boundary. GEO links need no handoffs at all, except for moving vehicles that cross from one beam into the next.

Inter-satellite laser links

A bent-pipe LEO satellite is useless unless a gateway is in view below it, which rules out mid-ocean and polar areas. Inter-satellite links (ISLs) fix that: satellites pass traffic to their neighbors until it reaches one above a gateway. Most use lasers, called optical ISLs.

The constellation becomes a mesh network in orbit whose links change shape all the time, so routing is recomputed continuously. Starlink's newer satellites carry laser links; Iridium has used radio crosslinks since the 1990s; ESA's European Data Relay System uses lasers to relay Earth-observation data from LEO satellites through GEO satellites. Mesh routing in general is in Mesh, IoT & autonomous systems.

Major systems as of late 2026

Numbers in this area change monthly; treat these as approximate snapshots.

GNSS (global navigation satellite systems) are covered in their own section below.

Direct to device

Direct to device (D2D, also direct-to-cell) means an ordinary phone talking to a satellite with no dish. It is hard: a phone's antenna is tiny and transmits a fraction of a watt, so the satellite needs a very large antenna or must accept very low data rates; and a satellite moving at 7.6 km/s shifts the frequency (Doppler shift) and changes the timing far more than a cell tower does.

Today D2D means messaging, emergency calls and low-rate data where there is no coverage, not a replacement for towers. Spectrum is the bottleneck: SpaceX agreed in 2025 to buy EchoStar's AWS-4 and H-block licenses (about 50 MHz of S-band spectrum in the US) for a next-generation direct-to-cell constellation. Status claims change quickly; check the carriers' own pages.

GNSS: positioning from time

GNSS satellites don't receive anything from you: each one broadcasts its exact position and the exact time from its onboard atomic clocks. Your receiver measures how long each signal took to arrive, multiplies by the speed of light to get a distance, and finds the one point that is the right distance from every satellite. This is trilateration.

distance = c × (time received − time sent)
 
c ≈ 300,000 km/s, so  1 µs of timing error ≈ 300 m
                      1 ns  of timing error ≈ 30 cm
 
unknowns: x, y, z and the receiver clock's offset
→ at least 4 satellites for a 3D fix

A phone's quartz clock is far too poor for nanosecond timing, so the receiver treats its own clock error as a fourth unknown and solves for it: GNSS gives the exact time as a side effect. Cell networks, power grids and financial systems rely on that.

• Error sources: the ionosphere and troposphere slow the signal (dual-frequency receivers measure and remove most ionospheric delay), reflections off buildings (multipath), small clock and orbit errors, and poor geometry when all visible satellites sit in one part of the sky.
• Corrections: SBAS (WAAS in the US, EGNOS in Europe) broadcast corrections from GEO satellites; RTK (real-time kinematic) uses a nearby base station to reach centimeters, for surveying, farming and drones.
• Relativity: the satellite clocks run fast by about 38 µs per day relative to the ground (gravity is weaker up there; their speed slows them a little), and the system corrects for it. Uncorrected, positions would drift by kilometers a day.
• Weak signals: GPS arrives at around −130 dBm, below the background noise; receivers recover it by correlating with a known code. That also makes jamming and spoofing (fake signals) easy, and both are increasingly common near conflict zones, affecting aircraft and ships.
• A-GNSS: phones download satellite orbit data over the mobile network to get a first fix in seconds instead of minutes.

Weather and rain fade

Water absorbs and scatters radio waves, more strongly the higher the frequency. Rain fade is the signal loss during rain: negligible in L and C band, a few decibels in Ku band in heavy rain, and in Ka band and above a severe storm can cost more than 10 dB, enough to cut a link. Snow on a dish and water on its cover add losses too. Each 3 dB halves the received power.

Rain statistics for each climate (the ITU-R P.618 model) tell a designer how much margin buys, say, 99.9% availability.

Debris, spectrum and launch

Orbital debris

ESA's 2025 Space Environment Report counts about 40,000 objects tracked by space surveillance networks, of which about 11,000 are working satellites, and estimates more than 1.2 million objects larger than 1 cm. At 7–8 km/s even a small fragment can destroy a satellite, and each collision makes more fragments: in the worst case a cascade, the Kessler syndrome.

• Collision avoidance: operators get conjunction warnings from tracking networks and maneuver; large constellations automate it.
• Low orbits clean themselves: air drag pulls dead satellites down. Starlink is moving about 4,400 satellites from 550 km to 480 km during 2026 so failures reenter sooner.
• Rules: since 2022 the US FCC requires US-licensed LEO satellites to deorbit within 5 years of their mission's end; GEO satellites are pushed up to a graveyard orbit about 300 km higher instead.

Spectrum and orbital rights

Radio waves cross borders, so satellite spectrum is coordinated internationally by the ITU (the UN's International Telecommunication Union) under its Radio Regulations. A national regulator files on its operator's behalf; the filing is coordinated with others who might interfere and recorded in the Master International Frequency Register, which protects it.

Launch

Launch was the cost that kept satellites rare. Reusable boosters, and satellites built to stack dozens to a rocket, changed that: constellations launch in batches, and satellites raise themselves from a low drop-off orbit to their working shell with their own thrusters, which also lets failed units be caught before they reach the shell. For a new constellation, launch supply is often the main schedule risk.

Putting a system together

1. Spectrum and licenses

   File with the ITU through a national regulator, coordinate with other operators, and get permission country by country to serve users and install gateways.

2. Design the constellation

   Choose altitude, planes, inclination and minimum elevation from where the customers are and how much capacity each square kilometer needs; decide bent pipe or regenerative, and whether to carry lasers.

3. Build and launch

   Mass-produce satellites, launch them in batches, raise their orbits, test each one, and budget for replacing the fleet every few years.

4. Build the ground segment

   Gateways near fiber and in places with good weather, POPs where the network peers with ISPs and content networks, TT&C stations to command the satellites, and an operations center.

5. Run the network core

   The operator runs its own IP network and autonomous system (Starlink's is AS14593), assigns addresses (often carrier-grade NAT for IPv4, plus IPv6), and exchanges routes over BGP like any ISP: see Autonomous systems & BGP.

6. Ship terminals and operate

   Manufacture and type-approve terminals, then continuously schedule beams and handoffs, balance load, dodge debris and retire old satellites.

The same parts in different proportions make every system above: GEO broadband is a few huge satellites and few gateways; a LEO constellation is thousands of small satellites, dozens of gateways per continent and lasers for the gaps; GNSS is a constellation that only broadcasts. How the pieces sit inside a full network is in Building networks.

Try it

• Watch satellites pass: a tracker such as Heavens-Above or a phone astronomy app shows when the ISS or Starlink trains cross your sky; a pass lasts minutes, which is the handoff problem made visible.
• Measure your path: on any connection, ping -c 20 1.1.1.1 shows the round-trip time. On GEO expect 600 ms or more, on LEO roughly 20–50 ms, with jumps when the network reconfigures.
• See GNSS at work: a GNSS status app lists the satellites your phone hears from each system and their signal strength; walk between tall buildings and watch accuracy drop.
• Compute passes yourself with the Skyfield (opens in a new tab) Python library and orbit data from CelesTrak (pip install skyfield):

from skyfield.api import load, wgs84
 
url = ("https://celestrak.org/NORAD/elements/gp.php"
       "?GROUP=stations&FORMAT=tle")
by_name = {s.name: s for s in load.tle_file(url)}
iss = by_name["ISS (ZARYA)"]
 
here = wgs84.latlon(40.71, -74.01)  # New York
ts = load.timescale()
t0 = ts.now()
t1 = ts.tt_jd(t0.tt + 1)  # the next 24 hours
 
times, events = iss.find_events(
    here, t0, t1, altitude_degrees=10.0
)
names = ("rise", "highest", "set")
for t, e in zip(times, events):
    print(t.utc_strftime("%Y-%m-%d %H:%M UTC"), names[e])

And the latency arithmetic from earlier, for any altitude:

C_KM_S = 299_792.458
 
def bent_pipe_rtt_ms(altitude_km: float) -> float:
    """Best case: 4 trips, satellite straight overhead."""
    return 4 * altitude_km / C_KM_S * 1000
 
for name, km in [("LEO", 550), ("MEO", 8_062),
                 ("GEO", 35_786)]:
    print(f"{name}: {bent_pipe_rtt_ms(km):.1f} ms")
# LEO: 7.3 ms, MEO: 107.6 ms, GEO: 477.5 ms

References

• Catalog of Earth Satellite Orbits (NASA Earth Observatory) (opens in a new tab): orbit types and why each is used
• Types of orbits (ESA) (opens in a new tab): LEO, MEO, GEO, polar and sun-synchronous, with diagrams
• Molniya orbit (Wikipedia) (opens in a new tab): the 63.4° highly elliptical orbit explained
• A multifaceted look at Starlink performance (RIPE Labs) (opens in a new tab): measured latency, throughput and the 15-second reconfiguration
• Starlink specifications (opens in a new tab): terminal models, power and field of view
• Phased array (Wikipedia) (opens in a new tab): beam steering by phase, grating lobes
• Non-Terrestrial Networks overview (3GPP) (opens in a new tab): satellite support in 5G and IoT standards
• GPS space segment (GPS.gov) (opens in a new tab): the official constellation description
• How satellite navigation works (ESA) (opens in a new tab): timing and trilateration
• Rain fade (Wikipedia) (opens in a new tab): causes, bands and mitigations
• ESA Space Environment Report 2025 (opens in a new tab): debris counts and trends
• Space services (ITU-R) (opens in a new tab): ITU satellite filings and coordination
• New milestones for non-geostationary satellite deployment (ITU) (opens in a new tab): the 10/50/100% constellation rule
• Skyfield: Earth satellites (opens in a new tab): computing passes from orbit data