Each pulse unit is a small fission charge dropped behind the pusher plate and detonated a set distance astern. The expanding plasma slams into the plate; an ablated surface layer carries momentum onto it. The impulse delivered is modelled from the pulse-unit's yield with a momentum-coupling coefficient Cm (the historical Project Orion feasibility studies estimated Cm on the order of 10³–10⁴ m/s for a polyethylene-coated plate):
E_pulse = Y_kt · 4.184×10¹² J
J = C_m · sqrt(2 · η · E_pulse · m_u) (impulse, N·s)
v_plate += J / m_plate (instant kick — sequential, not continuous thrust)
That kick would break a human spine if applied directly to the crew — Orion's real innovation was the two-stage pneumatic/mechanical shock absorber between the pusher plate and the ship. It is modelled here as a damped spring linking two masses, numerically integrated every frame:
m_p·v_p' = −k·x − c·(v_p − v_s)
m_s·v_s' = +k·x + c·(v_p − v_s)
x' = v_p − v_s (strut compression)
Between kicks, total momentum m_p·v_p + m_s·v_s is conserved by the strut — the spring-damper spreads the plate's sudden velocity spike over a fraction of a second, so the crew module feels a bounded acceleration instead of a shock. Because the coupling conserves momentum, the ship's cumulative Δv after many pulses converges toward the theoretical sum of impulses divided by total ship mass, N·J / m_ship — track this against the live "Theoretical Δv" readout and the plate-vs-ship velocity plot, which shows the plate's jagged pulse-driven spikes being smoothed into the ship's gradual climb.
- Yield per pulse — energy of each nuclear charge; sets impulse magnitude.
- Pulse interval — time between detonations in auto-fire.
- Strut stiffness / damping — the shock absorber's spring constant and damping coefficient.
- Detonate one pulse — fire a single charge and watch the strut compress and relax.
Real-world relevance: this is the propulsion concept studied by General Atomics under Project Orion (1958–1965) and revisited in modern mission-design papers as one of the few near-term technologies offering both high thrust and high specific impulse (Isp on the order of 10,000 s) for crewed deep-space missions.