Scenario

Coverage vs latitude: why a 53 degree constellation stops at 61 degrees

Inclination plus the coverage half-angle sets a hard latitude ceiling. Above it, no fleet size produces a single second of service.

A constellation at 53° inclination does not fade out gradually as you go north. It stops. Above 61° latitude, with a 25° elevation mask at 520 km, no satellite in the shell ever rises above the mask, and no number of satellites changes that. A thousand of them would still leave the site with zero seconds of service.

The arithmetic is short. A satellite at 520 km is visible above 25° out to a ground circle of radius 8.1° of arc. The highest latitude the orbit itself reaches is its inclination, 53°. Add the two and you get the service band edge at 61.1°. That is the whole derivation, and it is why this is a hard edge rather than a slope.

Loaded configuration: 48 satellites · 520 km · 53° inclination · min elevation 25° · latitude 55°

Scenario

SatellitesWalker 48/8/1

Orbital planes

Altitude520 km

Inclination53.0°

Min elevation25°

Service latitude55° 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 48/8/1 · 48 h window · 20 s step · worst of 8 longitudes at 55°

Worst outage

12.3 min

longest wait, worst longitude

Average wait

5.7 min

mean gap between windows

Windows / day

155

distinct service windows

Service / day

555 min

of 1440 min

Coverage

39%

time in view

Service timeline at your latitude

48 h · worst-case longitude at 55°

Longest gap 12.3 min. Filled blocks mark at least one satellite above 25° elevation.

Outage vs constellation size

Worst outageAverage wait

At 55° latitude, min elevation 25°, 520 km / 53.0°. Log scale. Labels mark the worst outage.

Worst outage vs latitude

48 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	5.7 h	2.4 h	9.7	35	2.4%
12 sats	4 × 3	75.0 min	33.5 min	38.7	139	9.6%
22 sats	11 × 2	35.7 min	16.7 min	70.9	255	17.7%
48 sats	8 × 6	12.3 min	5.7 min	154.7	555	38.5%
90 sats	10 × 9	3.0 min	1.5 min	258.6	1041	72.3%
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.

Worst outage across the band

Service latitude	Worst outage	Avg wait	Windows/day	Service min/day	Coverage
0° latitude	1.9 h	14.8 min	79.4	276	19.2%
20° latitude	63.7 min	12.8 min	87.2	304	21.1%
40° latitude	32.0 min	6.9 min	139.2	479	33.3%
50° latitude	5.7 min	3.7 min	177.2	779	54.1%
55° latitude	12.3 min	5.7 min	154.7	555	38.5%
58° latitude	13.7 min	9.9 min	113.6	318	22.1%
60° latitude	56.3 min	19.2 min	68.8	121	8.4%
62° latitude	no coverage	n/a	n/a	n/a	n/a
65° latitude	no coverage	n/a	n/a	n/a	n/a

48 satellites at 520 km, 53° inclination, minimum elevation 25°.

The best service in the whole table is not at the equator. It is at 53° or thereabouts, near the inclination itself, where the orbit lingers as it turns over. At latitude 50° the worst wait is 5.7 min. At the equator, with exactly the same fleet, it is 1.9 h. Satellites spend proportionally less time over the low latitudes they cross quickly, and more over the turning latitudes where the ground track doubles back.

The edge is worse than it looks

Service does not stay good right up to 61° and then vanish. It degrades sharply in the last few degrees, because near the edge a satellite only just scrapes above the mask, for a very short window, and only when the orbit is at the top of its swing. At 58° the worst wait is already 13.7 min and at 60° it is 56.3 min, against 5.7 min at 50°. Treat the last five degrees of any service band as marketing rather than coverage.

Three ways to move the edge

Raise the inclination: The direct lever, because it moves the first term of the sum. At 70° inclination the same altitude and mask push the edge to 78°. The cost is that the shell then spends more of its time over latitudes where nobody lives, so equatorial and mid-latitude service gets thinner for the same fleet size.
Relax the mask: Dropping the mask to 10° widens the coverage circle and moves the edge to 67°. This is a terminal decision rather than a space segment one, and it buys latitude at the price of link margin and interference at low angles.
Fly higher: Altitude widens the same circle. At 1200 km the edge moves to 68°. It is the weakest of the three levers per unit of pain, since path loss, radiation and deorbit obligations all get worse with altitude.

Why this matters commercially

Coverage maps drawn as a coloured band across a globe invite the reader to assume the band is uniform and that its edge is soft. Neither is true. If a prospect is at 55° and your shell is at 53°, you are selling into the part of the band where service is already several times worse than at the design latitude, and a customer forty degrees further north is not a smaller opportunity, it is not an opportunity at all until the inclination changes.

Move the service latitude slider through the whole range on this page and watch the marker cross the shaded band. The moment it enters the shaded region the tool stops producing numbers, on purpose. There is no honest number to give there.