Constellation shape
A 66-satellite near-polar shell, the Iridium pattern
What a 66-satellite near-polar shell at 780 km delivers as idealised geometry: the classic pattern for global voice and messaging, including the poles.
How the planes are arranged, and how this site arranges them. Every figure here comes from a Walker-delta shell: planes spread evenly around the whole circle of right ascension. The real fleet flies a star pattern, and its six planes sit about 32 degrees apart in the catalogue snapshot, spanning half the circle rather than all of it. Those are not the same arrangement. At this inclination, planes half a turn apart trace circles only 7.2 degrees apart over the ground, so spreading them around the whole circle spends half of them twice. At latitude 60 it makes no difference to the headline. It makes a great deal of difference further down the latitude chart: at 0 degrees this page shows 1.7 h where the shell arranged as it really flies gives 80 s. Every figure on this page is the site's arrangement, which for this shell is the pessimistic one.
66 satellites in 6 planes of 11, at 780 km and 86.4 degrees. The oldest still-flying answer to global coverage, and the one shape that genuinely serves the poles. Near-polar inclination reaches latitudes nothing else does, and what it costs at the equator depends far more on how the planes are arranged than on the inclination itself.
At latitude 60 with a 10 degree elevation mask, this shape gives a worst-case outage of 20 s, and about 1436 service minutes a day. The service band reaches the poles.
Across latitudes it is uneven, as most shells are. At the equator the worst outage is 1.7 h; at 70 degrees it is continuous service. Move the latitude control below to walk the whole range.
A 66-satellite near-polar shell, the Iridium pattern
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 60°Longest gap 20 s. Filled blocks mark at least one satellite above 10° elevation.
Outage vs constellation size
At 60° latitude, min elevation 10°, 780 km / 86.4°. Log scale. Labels mark the worst outage.
Worst outage vs latitude
66 sats · 780 km · 86.4° · min elevation 10°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 | 1.8 h | 66.3 min | 19.3 | 156 | 10.8% |
| 12 sats | 4 × 3 | 28.7 min | 23.0 min | 46.0 | 386 | 26.8% |
| 22 sats | 11 × 2 | 24.3 min | 20.5 min | 32.4 | 780 | 54.2% |
| 48 sats | 8 × 6 | 40 s | 21 s | 15.8 | 1435 | 99.6% |
| 66 sats | 6 × 11 | 20 s | 20 s | 11.7 | 1436 | 99.7% |
| 90 sats | 10 × 9 | continuous | 0 | 1 | 1440 | 100.0% |
| 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.
Which assumption this answer depends on
ranked by how far the answer movesEach row varies one thing by a plausible error and holds the rest still. The assumed errors are stated so you can disagree with them. Verify the top row before quoting the headline.
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.
Why near-polar
Inclination sets the highest latitude an orbit reaches, and the coverage circle around each satellite adds a little more. At 86.4 degrees this shell reaches everywhere: the worst outage at latitude 80 is continuous service, where a 53 degree shell of the same size and altitude gives nothing at all. That is the whole argument for near-polar geometry, and it is not a small one if your customers are ships, aircraft, or anything north of Scandinavia.
What it costs
Orbits converge at the poles and spread out at the equator, so a near-polar shell spends proportionally less time over the latitudes where most people live. The same 66 satellites give 1.7 h at the equator. A constellation is a choice about which customers to serve well, and this one chooses reach over density.
The mask decides the fleet
This page uses a 10 degree mask, which suits a handset with a stub antenna and a user willing to stand outside. Raise it to 25 degrees, the geometry a modern direct-to-device service needs, and the same 66 satellites give 15.7 min. Nothing about the shell changed. The requirement did.
Other shapes
- The Globalstar pattern: 48 satellites, mid-inclinationA 48-satellite shell at 1414 km and 52 degrees as idealised geometry: high altitude buying coverage per satellite, with a hard latitude ceiling.48 sats · 1410 km · 52° · 8 planes
- The OneWeb pattern: 648 satellites, polarA 648-satellite polar shell at 1200 km as idealised geometry: what a dense high-LEO constellation delivers at every latitude, including above the Arctic Circle.648 sats · 1200 km · 87.9° · 12 planes
- A dense broadband shell at 53 degreesThe shape most new broadband constellations reach for: a dense low shell at 53 degrees, sized for continuous service across populated mid-latitudes.720 sats · 550 km · 53° · 20 planes