Constellation sizing
How many satellites do I need?
State the service you have to promise. This searches fleet sizes and plane arrangements for the smallest constellation that delivers it, and tells you where the answer stops being reliable.
Result
30satellites
in 5 planes of 6, at 520 km and 53°, gives a worst outage of 12.7 min at 50° latitude.
The number to plan around
Open it in the calculator
Load this configuration to see the timeline, the latitude sweep and the full numbers.
How the search works
- Not a binary search. Worst outage is not monotonic in fleet size, so a search that assumes bigger is better returns confidently wrong answers. This brackets along a ladder, refines between the bracketing pair, then tries every plane arrangement near the winner.
- Planes are searched too. The automatic plane rule is revisit-friendly, not optimal. Searching count alone would overstate the fleet you need.
- Then it checks upward, one size at a time. Round numbers are exactly the sizes the plane rule arranges well, so stepping in tens would report a reassuring zero every time.
- Fidelity. The search runs at 4 longitudes and 60 second steps; the answer is confirmed at 8 longitudes and 20 second steps, which is what the rest of the site quotes. Full method.
Why there are three numbers and not one
The smallest fleet that meets a target is the number everyone asks for. It is also, on its own, misleading, because coverage does not improve smoothly as you add satellites. The automatic plane rule gives a prime fleet one satellite per plane, which is a poor arrangement, so the curve saws rather than falls.
With a fifteen minute target at 520 km and 53 degrees, serving latitude 50, the smallest fleet that meets it is 30 satellites. Nine sizes above that miss it, including every prime in the range: 31 satellites give around 54 minutes, worse than 22. The target only stays met from 48 upward. Quote 30 to a customer and you have said something true that will embarrass you the first time the deployment lands on 31.
So the tool reports all three: the smallest that meets your target, the size from which it stays met, and the sizes in between that fail. Plan around the second, quote the first only with the third in front of you.
What this is not
A geometric floor for an idealised shell, and nothing more. Real buildouts need more satellites than this says, because real fleets deploy into fewer planes than the final design, drift out of perfect phasing, carry beams narrower than the visible cone, and run out of capacity before they run out of geometry. Read the answer as the best case the geometry allows, then add what reality charges.