Scenario
Direct-to-phone coverage at 5, 25, 45 and 90 satellites
What a direct-to-device constellation can promise at each stage of a buildout, from a first block of five satellites to a 90-satellite shell.
Direct-to-device service has an unusually demanding geometry. An unmodified handset has a small antenna, no pointing and a body in the way, so the satellite has to be high in the sky before the link closes. That is why this page uses a 25° elevation mask rather than the 10° a gateway dish would accept, and it is the single assumption that most changes the answer.
At 520 km and 53° inclination, serving a customer at latitude 40°, the buildout looks like this: 3.8 h of worst-case outage at five satellites, 81.0 min at twenty-five, 16.0 min at forty-five and 6.3 min at ninety.
Loaded configuration: 25 satellites · 520 km · 53° inclination · min elevation 25° · latitude 40°
Direct-to-phone coverage at 5, 25, 45 and 90 satellites
A against B
B is drawn dashed on the charts below, in the same colours.
Service timeline at your latitude
48 h · worst-case longitude at 40°Longest gap 81.0 min. Filled blocks mark at least one satellite above 25° elevation.
Outage vs constellation size
At 40° latitude, min elevation 25°, 520 km / 53.0°. Log scale. Labels mark the worst outage.
22 satellites do better here than 25: 30.3 min against 81.0 min. Coverage depends on how the planes interleave, not only on the count, and the automatic rule arranges each fleet size differently. Why this happens.
Worst outage vs latitude
25 sats · 520 km · 53.0° · min elevation 25°Latitude sweep is sampled at 60 s steps across 4 longitudes, so it is coarser than the headline figures.
Numbers
| Constellation | Planes | Worst outage | Avg wait | Windows/day | Service min/day | Coverage |
|---|---|---|---|---|---|---|
| 3 sats | 3 × 1 | 6.6 h | 2.7 h | 8.8 | 30 | 2.1% |
| 12 sats | 4 × 3 | 4.1 h | 37.3 min | 34.8 | 120 | 8.3% |
| 22 sats | 11 × 2 | 30.3 min | 19.2 min | 63.9 | 220 | 15.2% |
| 25 sats | 5 × 5 | 81.0 min | 19.6 min | 61.6 | 232 | 16.1% |
| 48 sats | 8 × 6 | 32.0 min | 6.9 min | 139.2 | 479 | 33.3% |
| 90 sats | 10 × 9 | 6.3 min | 3.9 min | 173.3 | 764 | 53.1% |
| 200 sats | 20 × 10 | 1.7 min | 71 s | 123.4 | 1294 | 89.9% |
Same sampling as the headline tiles: 8 longitudes, 20 s steps (40 s above 400 satellites). Every row except your own uses the automatic plane rule.
Model and assumptions
- Geometry: spherical Earth (R = 6371 km), circular orbits, Walker-delta constellation with evenly spaced planes and phasing F = 1, no J2 drift or drag. Service means at least one satellite above the minimum elevation angle.
- Sampling: headline numbers and the table simulate 48 h (96 h for fleets of 12 or fewer) at 20 s steps, worst-cased across 8 longitudes at your latitude. The latitude chart uses 60 s steps and 4 longitudes.
- Planes: "Auto" spreads satellites across the divisor of N nearest above the square root of N, a revisit-friendly default. Real constellations may choose otherwise: a single-plane test block clusters its passes.
- Fidelity: planning-grade, for sizing intuition and commercial conversations. Contractual coverage commitments need full-fidelity tooling (STK, GMAT) with real ephemerides, beam patterns and link budgets. This tool models geometry only, not capacity or link margin. Full method and validation anchors.
What each stage can honestly be sold as
| Constellation | Planes | Worst outage | Avg wait | Windows/day | Service min/day | Coverage |
|---|---|---|---|---|---|---|
| 5 sats | 5 × 1 | 3.8 h | 1.6 h | 14.4 | 50 | 3.4% |
| 25 sats | 5 × 5 | 81.0 min | 19.6 min | 61.6 | 232 | 16.1% |
| 45 sats | 9 × 5 | 16.0 min | 11.2 min | 95.3 | 371 | 25.8% |
| 90 sats | 10 × 9 | 6.3 min | 3.9 min | 173.3 | 764 | 53.1% |
At 520 km, 53° inclination, minimum elevation 25°, latitude 40°.
Five satellites: a demonstration, not a service
Roughly 50 minutes of visibility a day, in a handful of windows, with up to 3.8 h of silence between them. This is enough to prove a link works and to shoot a launch video. It is not enough to sell a subscription, and the honest framing in a customer conversation is scheduled connectivity rather than coverage.
Twenty-five satellites: intermittent messaging
About 232 service minutes a day, with an average wait of 19.6 min and a worst case of 81.0 min. Store-and-forward messaging works here. Emergency SOS works here, because the user is willing to wait and the product is designed around waiting. Anything that expects to place a call at a moment of the user's choosing does not.
Forty-five satellites: usable messaging, near-usable voice
Worst outage drops to 16.0 min and daily service to about 371 minutes. The failure mode changes character. Users stop experiencing outages as absence of service and start experiencing them as a bad few minutes.
Ninety satellites: continuous enough to sell as coverage
6.3 min of worst outage and roughly 764 minutes a day. At this point the constellation, not the schedule, is the product. Note that this is still not continuous at a 25° mask, and closing the last few minutes costs more satellites than the whole first half of the buildout did.
Two assumptions worth testing before you quote a number
The mask. If the link actually closes at 10° rather than 25°, the same forty-five satellites give 4.3 min of worst outage instead of 16.0 min. Half the argument about fleet size is really an argument about link budget. Change the minimum elevation control and watch the whole picture move.
The plane spread. Every row above assumes satellites are already spread across planes. Five satellites launched together into one plane give 15.7 h of worst outage instead of 3.8 h, from the same hardware in orbit. Early fleets are almost always single-plane fleets, which is covered on thesingle-plane page.
Geometry is the ceiling, not the service. A satellite being visible is necessary for a call and nowhere near sufficient: beams have to be pointed at that cell, spectrum has to be cleared with the terrestrial licensee, and capacity has to exist for the users underneath. Those constraints only ever subtract from the numbers on this page.
Other scenarios
- Why continuous coverage is not a thresholdContinuity depends on the elevation mask, altitude, latitude and plane arrangement, not on a satellite count. The explanation behind the sizing tool.
- IoT store-and-forward with a polar constellationRevisit time for a sun-synchronous IoT constellation with a 10 degree mask, where the product is message latency rather than continuous service.
- Why single-plane deployments have long outagesThe same satellite count can mean a 15 hour outage or a 25 minute one. Deployment order and plane spread decide which.
- Coverage vs latitude, and why 53 degrees stops at 61Inclination plus the coverage half-angle sets a hard latitude ceiling. Above it, no fleet size produces a single second of service.