Presets
Playback
Launch and disposal policy
Single-shell phase plane
Model checks
The science
Collision rate and cascade
Objects are treated like a gas. A pair in one shell collides at rate σ vrel / V per pair, with σ = π(r1+r2)2, vrel = (4/3) vcirc for random orbit planes and V the shell volume. A collision above 40 J/g specific energy is catastrophic and the simplified NASA breakup law N(>Lc) = 0.1 M0.75 Lc−1.71 gives the number of new tracked fragments. Drag lowers a circular orbit at da/dt = −CD (A/m) ρ √(μa) with a piecewise exponential atmosphere.
Phase plane
For one shell, dN/dt = L − N/τ + k N2: inflow L, drag lifetime τ and collisional fragment gain k. Real roots exist only if L < Lcrit = 1/(4 k τ2); the lower root is stable, the upper one is the tipping point beyond which the count grows without bound. Higher shells have larger τ and a much lower Lcrit.
Honest simplifications: shell-averaged populations hand-shaped for illustration (not a catalogue), isotropic orbit planes, circular orbits, three object classes, a simplified breakup model and fixed mean masses. The numbers show trends, not a forecast. Same physics module as the 3D page.
What to try
- Press Poor disposal at 850 km or High orbit and watch red rings appear and the count climb.
- Compare Today with Clean-up: active removal.
- Move the inspected altitude from 500 to 1000 km: the critical inflow collapses by orders of magnitude.
- Set the inflow multiple above 1 and see the phase plane lose its fixed points.