Constellation planning · estimator
LEO constellation revisit time calculator
How often does a constellation of N satellites actually pass over your customer? Set the fleet, the orbit and the service geometry, then read the worst-case outage, the average wait and the minutes of service per day at any latitude.
Constellation estimate
A against B
B is drawn dashed on the charts below, in the same colours.
Service timeline at your latitude
96 h · worst-case longitude at 50°Longest gap 29.3 min. Filled blocks mark at least one satellite above 25° elevation.
Outage vs constellation size
At 50° latitude, min elevation 25°, 520 km / 53.0°. Log scale. Labels mark the worst outage.
Worst outage vs latitude
12 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 | 4.0 h | 1.9 h | 12.5 | 49 | 3.4% |
| 12 sats | 4 × 3 | 29.3 min | 24.9 min | 50.0 | 197 | 13.7% |
| 22 sats | 11 × 2 | 25.7 min | 11.8 min | 91.8 | 361 | 25.1% |
| 48 sats | 8 × 6 | 5.7 min | 3.7 min | 177.2 | 779 | 54.1% |
| 90 sats | 10 × 9 | 3.3 min | 73 s | 88.6 | 1333 | 92.5% |
| 200 sats | 20 × 10 | continuous | 0 | 1 | 1440 | 100.0% |
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 this answers
Satellite trackers tell you where a spacecraft is right now, or when it will next fly over your back garden. That is a different question from the one a constellation operator gets asked in a sales meeting: if we fly N satellites at altitude A and inclination I, what can we promise a customer at latitude X?
This calculator answers that one in commercial units. The worst outage is the longest a user at your latitude can wait with nothing overhead, taken across the whole latitude circle rather than at one convenient longitude. The average wait is the mean gap between service windows. Service minutes per day is what you can actually sell. The size chart shows how those numbers collapse as the fleet grows, which is usually the point of the conversation: continuous service is not a gradual improvement, it arrives suddenly once the shell closes.
Worked scenarios
Each page below opens the calculator with a configuration already loaded and explains what the numbers mean for that kind of service.
- 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.90 sats · 550 km · 53° · min elev 25° · lat 50°
- Direct-to-phone coverage at 5, 25, 45 and 90 satellitesWhat 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.25 sats · 520 km · 53° · min elev 25° · lat 40°
- 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.22 sats · 550 km · 97.5° · min elev 10° · lat 60°
- 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.5 sats · 520 km · 53° · min elev 25° · lat 40°
- 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.48 sats · 520 km · 53° · min elev 25° · lat 55°
Reading the model honestly
The model is geometric. A satellite is either above your elevation mask or it is not, and the constellation is an idealised Walker-delta shell with evenly spread planes. Real fleets drift, deploy out of order, carry beams that do not cover the whole visible cone, and run out of capacity long before they run out of geometry. Every one of those effects makes real service worse than the number on this page, never better.
The charts keep two labelled bands for the cases where a number would be dishonest. A point in the continuous band means no gap was found at all. A point in theno revisit in window band means fewer than two passes happened in the whole simulated period, so the true gap is longer than the window and this tool will not guess it.