Constellation shape

A dense broadband shell: 720 satellites at 53 degrees

The shape most new broadband constellations reach for: a dense low shell at 53 degrees, sized for continuous service across populated mid-latitudes.

720 satellites in 20 planes of 36, at 550 km and 53 degrees. The modern default for consumer broadband: low enough for latency, inclined to sit over the latitudes where customers actually live, and dense enough to hold a 40 degree mask.

At latitude 45 with a 40 degree elevation mask, this shape closes: no gap at any sampled longitude, a full 1440 service minutes a day. The service band reaches 58 degrees of latitude.

Across latitudes it is uneven, as most shells are. At the equator the worst outage is 22.7 min; at 70 degrees it is no coverage at all. Move the latitude control below to walk the whole range.

Scenario

SatellitesWalker 720/20/1

Orbital planes

Altitude550 km

Inclination53.0°

Min elevation40°

Service latitude45° N/S

Latitude only. Results are worst-cased around the whole latitude circle, so this is the band a city sits on rather than the city itself.

Walker delta 720/20/1 · 48 h window · 40 s step · worst of 8 longitudes at 45°

Worst outage

none

continuous service

Average wait

no gaps

Windows / day

one unbroken window

Service / day

1440 min

of 1440 min

Coverage

100.0%

time in view

Service timeline at your latitude

48 h · worst-case longitude at 45°

Continuous service. No gaps at this latitude.

Outage vs constellation size

Worst outageAverage wait

At 45° latitude, min elevation 40°, 550 km / 53.0°. Log scale. Labels mark the worst outage.

Worst outage vs latitude

720 sats · 550 km · 53.0° · min elevation 40°

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	5.0 h	3.3 h	7.1	16	1.1%
12 sats	4 × 3	3.9 h	47.8 min	28.4	63	4.4%
22 sats	11 × 2	47.7 min	25.6 min	51.9	115	8.0%
48 sats	8 × 6	42.7 min	10.5 min	113.6	251	17.4%
90 sats	10 × 9	20.0 min	4.6 min	212.4	469	32.6%
200 sats	20 × 10	3.3 min	1.8 min	333.2	830	57.6%
720 sats	20 × 36	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.

Why 53 degrees keeps being chosen

An inclination of 53 degrees is close to a population-weighted optimum for the northern hemisphere. The shell spends most of its time over the latitudes where customers, cities and money are, rather than over ocean and ice. It is a commercial decision expressed as an orbital element.

The cost is a hard ceiling. With a 40 degree mask at 550 km, service ends at 58 degrees. At latitude 60, which is Helsinki, Oslo and Stockholm, this shape gives no service at all. Every operator flying this shape and selling to the Nordics needs a second, higher inclination shell, and that is exactly why they build one.

The 40 degree mask is the expensive part

A broadband user terminal wants the satellite high in the sky: a steep look angle means shorter path, less atmosphere, and less chance of a roof or a tree in the way. That 40 degree mask is what forces the fleet size. Relax it to 25 degrees, the geometry a phone would accept, and the same 720 satellites give continuous service. Half the argument about constellation size is really an argument about terminal design.

Half the fleet is not half the service

At 360 satellites in the same 20 planes, the worst outage is 60 s. Continuous service is not approached gradually. It arrives when the shell closes, and until then the service is intermittent in a way no amount of marketing language fixes.

This shape is deliberately not attributed to any operator. A 53 degree low shell is a common design rather than one company's, and naming it after a fleet would claim more than idealised geometry can support.