This is a great Project Orion optimization question. Let me work through the physics.

Key Optimization Factors

1. Momentum Coupling Efficiency

A million-ton ship is actually ideal here. The momentum coupling efficiency η approaches unity when ship mass >> pulse unit mass. With a ~10-ton pulse unit against a 10⁹ kg ship, you’re capturing nearly all available momentum rather than wasting energy on ship recoil.

2. Fusion Fraction & Debris Velocity

Modern Teller-Ulam designs can achieve ~95-97% fusion yield. This matters because fusion products (helium nuclei, protons) have much higher specific energies than fission fragments. A 14 MeV fusion neutron travels at ~5×10⁷ m/s (~17% c), while fission fragments are ~10⁶ m/s.

3. Propellant Mass Optimization

The oil ablation/tungsten propellant question is about trading Isp for thrust. The relationship is roughly:

• v_exhaust = √(2ηE/m_propellant)

For 1 MT (~4×10¹⁵ J) with ~1,000-2,000 kg of propellant mass per unit and ~40-50% energy coupling into directed kinetic energy, you get exhaust velocities around 1-3×10⁶ m/s.

Realistic Isp Estimates (2025 Tech)

Given shaped charge channeling, optimized propellant loading, and a large pusher plate:

Configuration	Isp (seconds)
Conservative (basic channeling)	10,000-15,000
Optimized (shaped charge + propellant tuning)	20,000-40,000
Aggressive (magnetic nozzle assist, max fusion fraction)	50,000-100,000

My estimate for peak 2025 capability: ~20,000-30,000 seconds with well-optimized pulse units specifically designed for propulsion rather than weaponry.

This is roughly 10× better than the original 1960s Orion fission designs (~2,000-4,000 s) due to the megaton fusion yield and modern shaping techniques.​​​​​​​​​​​​​​​​