Which engine should capture a 1,000-tonne rock? The honest answer from the Resident’s Ledger asteroid-capture arc: it depends on how long you are willing to wait — and the dependency is strong enough to draw.
This experiment plots the strategy space in three dimensions:
- X: required Δv (m/s, log) — what the engine must deliver. This shrinks with patience, because longer horizons let gravity assists, lunar flyby tours, and ballistic capture through the Earth–Moon weak stability boundary absorb more of the work.
- Y: consumables (kg, log) — what the mission spends: xenon, fissile fuel, or chemical propellant. The photonic option spends nothing but patience.
- Z: authority (N, log) — thrust × control bandwidth: how much trajectory change can be commanded on demand.
Four candidate strategies float in this space at the rock’s current Δv: the photonic wrap + skirt with micro-charges (no engine at all), a small solar-electric ion system, the self-burrowing fission candle, and a chemical stage for reference. Infeasible candidates grey out; the dominant one glows.
The slider is the argument
Drag the time horizon from 1 to 20 years and the rock travels left through three zones:
- Zone C (Δv > 300 m/s): candle territory. Only fission’s energy density delivers km/s-class work for kilograms of fuel.
- Zone B (10–300 m/s): electric territory. A kW-class ion drive covers this for tonnes of xenon — and unlike the candle, it does not consume the rock as propellant. This zone only exists at long horizons.
- Zone A (Δv < 10 m/s): no engine at all. The photonic wrap’s free trim (~0.6 m/s per year with a 2,000 m² skirt) covers the entire budget. At τ = 20 years the rock arrives here.
The meta-move: patience moves rocks down through the zones, and time spent surveying fills the catalog with candidates already in the bottom zone. The dominant strategy at long horizons is not an engine — it is selection.
Caveats on the axes
The required-Δv curve (3000·e^(−0.28τ) m/s) is a cartoon of low-energy transfer mechanics, honest in shape but not in coefficients. The candle’s true cost includes consuming the rock itself as propellant (~10% of its mass at 300 m/s) — fine for location-value rocks, expensive for composition-value ones. Authority numbers are representative, not computed.