Fissile Fuel vs Capture Time Horizon

Model: 1,000-tonne near-Earth asteroid, 3 km/s capture delta-v, 80 TJ/kg fission energy, 5% burnup, silicate propellant at ~10 MJ/kg effective latent heat. Curves show required fissile fuel (U-235/Pu-239) as the capture timeline lengthens, accounting for heat loss to the surrounding rock. Lower-Isp variants consume more rock and lose more energy to conduction. The dashed green curve adds a photonic wrap + 2,000 m² reflective skirt: free solar-radiation trim reduces the delta-v the candle must deliver. The dashed gray curves (right axis) show the free photonic delta-v itself, with and without the skirt — note the units: meters per second. Photonics is a trim story, not a capture story.