Every step integrates Newton's second law in Earth's rotating reference frame with 4th-order Runge-Kutta:
a = -GM·r/|r|³ (gravity)
- ½ρ(h)·Cd·A/m·|v|·v (drag, h < 100 km)
- 2·Ω×v (Coriolis, Ω = Earth's spin)
- Gravity uses the true inverse-square law GM/r² pointing at Earth's centre, not a flat "g down" — realistic for altitudes of hundreds of km.
- Drag only acts below the Kármán line (100 km) with an exponential atmosphere ρ(h) = ρ₀·e^(-h/8.5km), so it bites during boost and re-entry but vanishes at apogee.
- Coriolis (F = 2mΩv·sinφ) is why the orange "actual" missile lands away from the grey reference: Earth keeps rotating under the missile during its ~20-30 min flight, deflecting it to the right in the northern hemisphere.
- Near 45° elevation with a 6-7 km/s burnout gives intercontinental range (thousands of km) and apogee altitudes above 1,000 km — genuinely sub-orbital, since surface orbital velocity is ≈7.9 km/s.