Deceleration uses magnetic field geometry modulation (cymatics-like reshaping), not physical rotation. The ship orientation never changes. The funnel's magnetic topology reverses to redirect captured medium forward instead of aft.
Momentum Transfer (Relativistic)
Medium (ISM or stellar wind) enters funnel at ship velocity: p_in = ṁ·γ_ship·v_ship
Field redirects medium forward at v_exit: p_out = ṁ·γ_out·v_exit
This is ~2× the force of simply catching the ISM (inelastic capture gives only F = ṁ·γ·v), because the redirected momentum adds to the captured momentum.
With TE/Kilopower Energy Addition
Energy per unit mass of redirected medium: (γ_out − 1)c² = (γ_in − 1)c² + P_avail/ṁ
So: γ_out = γ_in + P_avail/(ṁ·c²), and v_out = c·√(1 − 1/γ_out²)
Adding energy increases v_out > v_in, amplifying the braking force beyond passive reflection.
Stellar Wind Enhancement
ISM density: ρ_ISM ≈ 2×10⁻²³ kg/m³ (Local Bubble)
Stellar wind at 1 AU from target: ρ_wind ≈ 8×10⁻²¹ kg/m³ (Sun-like) — 400× denser
Wind density scales as 1/r²: ρ(r) = ρ_1AU / r²
Astrosphere boundary: ~500 AU from star. Inside this, stellar wind dominates ISM.
At 10 AU: ρ ≈ 8×10⁻²³ (8× ISM). At 1 AU: ρ ≈ 8×10⁻²¹ (400× ISM). At 0.1 AU: ρ ≈ 8×10⁻¹⁹ (40,000× ISM).
Braking effectiveness increases dramatically on final approach.
⚠️ Braking Simplifications
Stellar wind assumed radially symmetric and steady-state.
Braking trigger is heuristic (estimated stopping distance ≤ remaining distance).
No trajectory optimisation — constant braking once engaged.
Magnetic field efficiency for momentum reversal assumed 100%.