Megaconstellation Drag Decay & Station-Keeping

Shell Setup

Initial altitude 550 km

Solar activity Moderate

Area-to-mass ratio (A/m) 0.020 m²/kg

Time acceleration 6 sim-days/s

Live Readouts

Altitude

550.0 km

Orbital period

95.6 min

Decay rate

0.00 km/day

Sim elapsed

0.0 days

Station-keeping Δv spent

0.0 m/s (0.00 kg propellant)

How it works

A megaconstellation shell orbiting at 300–600 km sits inside the thin tail of Earth's thermosphere. Residual air drag steadily removes orbital energy; for a circular orbit of semi-major axis a this gives the standard first-order decay rate:

da/dt = − Cd · (A/m) · ρ(a) · v(a) · a
v(a) = √(GM/a)          (circular orbital speed)
ρ(a) = ρ₀ · exp(−(a−a₀)/H)   (exponential atmosphere, per altitude band)

Cd·(A/m) is the ballistic drag term — a flatter, lighter satellite (higher area-to-mass ratio) decays faster. ρ is not constant: solar UV/EUV heating inflates the thermosphere, so the same altitude can be several times denser at solar maximum than solar minimum — the slider applies a realistic density multiplier on top of the exponential profile.

Left to decay, a satellite's altitude falls faster and faster as it drops into denser air (a runaway), until it reaches roughly 150 km and re-enters within hours — which is why a dead VLEO satellite deorbits naturally in a few years rather than becoming permanent debris. To hold a working shell at constant altitude instead, an ion or Hall-effect thruster must continuously restore the lost velocity:

Δv rate ≈ ½ · Cd · (A/m) · ρ(a) · v(a)²   (thrust needed to cancel drag deceleration)
propellant mass ≈ m_dry · (1 − e^(−Δv / (Isp·g₀)))     (Tsiolkovsky rocket equation, Isp ≈ 1600 s)

Let orbit decay — thrusters off; watch the shell sink and the decay rate accelerate.
Station-keep — thrusters fire continuously to hold altitude; the panel accumulates the Δv and propellant this costs a ~260 kg satellite over the simulated time.
Solar activity — solar maximum can inflate density at 550 km by roughly an order of magnitude versus solar minimum, directly multiplying the decay rate or the fuel bill.

Real-world relevance: this trade — cheap natural deorbit for dead hardware versus a real, recurring propellant cost to keep thousands of satellites on station — is exactly why operators like Starlink and OneWeb fly in VLEO with electric propulsion rather than the higher, drag-free orbits used by older single-satellite missions.

⚠ Shell has re-entered — reset to try again

Satellite shell Thermosphere (drag zone)

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