Function oberth_dv_gain 

pub fn oberth_dv_gain(
    mu: Mu,
    r_periapsis: Km,
    v_inf: KmPerSec,
    burn_dv: KmPerSec,
) -> KmPerSec

Effective velocity change from a burn performed at periapsis of a hyperbolic flyby.

When a spacecraft with hyperbolic excess speed v_inf performs a prograde burn of magnitude burn_dv at periapsis distance r_periapsis from a body with gravitational parameter mu, the resulting change in v_inf (at infinity) is larger than the burn_dv alone — this is the Oberth effect.

v_periapsis = sqrt(v_inf² + 2μ/r_p) v_periapsis_after_burn = v_periapsis + burn_dv v_inf_after = sqrt(v_periapsis_after_burn² - 2μ/r_p) oberth_gain = (v_inf_after - v_inf) - burn_dv

Returns the Oberth gain: the extra Δv_inf beyond what the burn alone provides. A positive value means the burn was amplified by the gravity well.

All velocities in km/s, distances in km, mu in km³/s².