Function gravity_gradient_torque 

pub fn gravity_gradient_torque(
    gm_m3_s2: f64,
    distance_m: f64,
    mass_kg: f64,
    length_m: f64,
    angle_rad: f64,
) -> f64

Gravity gradient torque on an elongated spacecraft (N·m).

In a gravity field, a non-spherical body experiences torque that tends to align its long axis radially. For a cylinder of length L: τ ≈ 3 * μ * (I_zz - I_xx) * sin(2θ) / (2 * r³) where θ is the angle between the long axis and the local vertical.

Returns torque in N·m. Inputs: GM (m³/s²), distance (m), mass (kg), length (m), angle from vertical (rad).