Newton's second law drives the rocket directly — no scripted flight path. Every frame integrates real forces:
m·a_y = F_thrust,y − m·g
m·a_x = F_thrust,x + F_wind
F_wind = ½·ρ·Cd·A·(v_wind − v_x)·|v_wind − v_x|
ṁ = −F_thrust / (Isp·g0) (Tsiolkovsky depletion)
The autopilot ignites the "suicide burn" the instant coasting further would make a soft touchdown impossible: it inverts v² = v₀² − 2·a·d for the ignition altitude h_ign = v_y² / (2·a_max), using the current thrust-to-weight ratio for a_max. A PD controller (F_x = −Kp·x − Kd·v_x, gains scaled by the guidance-precision slider) steers a slice of thrust sideways to cancel crosswind drift, gimballed within the engine's real thrust budget.
- Wind — quadratic aerodynamic drag (ρ=1.225 kg/m³, Cd=0.8, A=3 m²), not a fudge factor.
- Fuel — burns off with mass proportional to thrust used ÷ (Isp·g₀), so a low-fuel margin genuinely lowers max deceleration late in the burn.
- Landing check — success requires touchdown speed ≤ 4.5 m/s, drift ≤ 18 m and low tilt; anything past that is a crash, shown as a debris burst.