A constellation, designed where it flies.
A Walker-delta 24/3/1 constellation at 550 km and 53° inclination — the shape of a modern low-Earth-orbit fleet — propagated with two-body dynamics and J2 nodal precession, its coverage and ground-station contacts worked out over a 3D globe. From a single orbit to a fleet-sizing trade and a verification sign-off, the whole mission-design loop in one program.
From one orbit to a verified fleet.
Each stage is its own runnable notebook, building from a single propagated orbit up to constellation-level coverage and a sizing trade.
Orbit propagation
Two-body motion plus the J2 oblateness perturbation, propagated from classical elements — the ground track drifts ~24° west each period as the Earth turns beneath it.
Walker constellation
The 24/3/1 recipe places every satellite's RAAN and mean anomaly from the i:T/P/F rule — all 24 orbits rendered at true altitude on the globe, coloured per plane.
Coverage & revisit
An elevation-mask footprint (~15° half-angle, ~1665 km) tiled across the constellation gives a 3D choropleth of how many satellites see each point — and a band coverage near 93%.
Contact windows
For a ground station at Toulouse, every pass above 10° elevation over 24 hours — about 140 passes a day, ~7 minutes mean — laid out as a timeline and an hourly histogram.
Sizing trade
A sweep over planes × satellites-per-plane plots fleet size against worst-case revisit, and lands the 24/3/1 baseline at the cost-versus-service knee.
J2 precession
The oblateness-driven node regression of −4.49°/day, separated from the Keplerian baseline and used to search for repeat ground tracks.
Coverage you can see, not just tabulate.
The constellation, its ground tracks and its instantaneous coverage all render on a 3D globe through the same notebook outputs that drive the numbers — orbits at true altitude coloured per plane, footprints extruded by how many satellites are in view. The propagation honours the J2 perturbation, the dominant secular effect at 550 km, so the node regression and repeat-track geometry are physical, not Keplerian idealisations. The mission-design loop — propagate, cover, contact, size, verify — lives in one place instead of three.
Mission requirements, re-derived and checked.
The sign-off notebook re-derives each requirement from the propagated constellation rather than restating the design intent.
| Result | Target | |
|---|---|---|
| Band coverage (24 h) | ~93% | ≥ 90% |
| Worst-case revisit | ≤ 6 h | ≤ 6 h |
| Passes per day (Toulouse) | ~140 | — |
| J2 node regression | −4.49°/day | physical |
| Requirements verified | 6 / 6 | PASS |
Mission-design fidelity.
Propagation is two-body plus J2 — the dominant secular perturbation at this altitude — not a full force model with drag, higher-order gravity, solar radiation pressure or third-body effects. The coverage footprint is a spherical-Earth elevation-mask cap on coarse grids, and revisit is evaluated over a 24-hour window. That is exactly the fidelity constellation sizing needs first: choosing planes and phasing, checking coverage and revisit, and counting ground-station contacts — before a high-precision orbit-determination tool ever enters the picture.
Design your own constellation.
Book a walkthrough and we'll set up your orbit, fleet geometry and ground stations, and run the coverage, contact and sizing studies live on the globe.