Thermal management for volatile preservation during excavation

Background

The dual bucket-wheel excavation system validated in rq-0-26 generates approximately 50 kW of waste heat during continuous operation. For the water-first resource strategy (rq-0-27), preserving volatiles (water ice, organics) during excavation is critical — but mechanical excavation generates heat through friction, and uncontrolled heating of volatile-rich regolith can cause premature sublimation, losing the most valuable resource fraction before it reaches the processing station.

Why This Matters

Volatile loss during excavation directly reduces:

• Water extraction yield from each tonne of excavated material
• Economic return of the water-first strategy
• Propellant production capacity
• Overall ISRU system efficiency

If excavation-induced heating causes 20-50% volatile loss, the effective water content of delivered material drops from 10-20% to 5-15%, requiring proportionally more material throughput to meet propellant production targets. This cascades into higher excavation rates, more robot wear, and increased power consumption.

Key Considerations

• 50 kW waste heat distributed across bucket-wheel contact area and housing
• Asteroid surface temperatures vary from ~100 K (shadowed) to ~400 K (sunlit)
• Water ice sublimation begins at ~150 K in vacuum
• Mechanical friction at cutting surfaces creates localized hot spots
• Excavated material in transit from bucket to hopper continues to warm
• Enclosed housing (required for particle containment) traps waste heat
• Shorter material dwell time in heated zones reduces volatile loss

Research Directions

1. Thermal modeling of excavation process: Model heat generation and transfer during bucket-wheel excavation of volatile-bearing regolith, quantifying volatile loss as a function of operating parameters.

2. Shadow-side excavation strategy: Evaluate operational concepts where excavation occurs on the shadowed side of the asteroid to minimize solar heating contribution and leverage cold sink temperatures.

3. Active cooling of cutting surfaces: Design heat rejection systems for bucket teeth and housing that limit contact temperature below volatile sublimation thresholds.

4. Material transfer optimization: Minimize dwell time of excavated material in heated zones through rapid transfer mechanisms between excavator and sealed transport containers.

5. Volatile loss budget: Establish acceptable volatile loss percentages at each stage (excavation, transfer, storage, transport) to define thermal requirements for the complete material handling chain.