Radiator durability and contamination over decades

Background

The Manufacturing Expansion BOM item specifies autonomous manufacturing nodes requiring 35-60 MW of thermal rejection capacity, with radiator areas exceeding 12,000 m² per node. These thermal management systems are critical infrastructure enabling the 20-50 MW electrical power generation and high-temperature refining processes (solar furnace smelting at 1,800°C, Molten Oxide Electrolysis operations) that drive swarm component production. The consensus document establishes a 25-year operational design life for manufacturing nodes, creating a fundamental tension between the aggressive thermal loads, the harsh space environment, and the longevity requirements. All three source models independently flagged radiator durability as a critical bottleneck lacking validated lifetime data.

The divergent views on thermal rejection methodology—conventional radiator panels (Claude: 210t mass allocation), droplet radiators using liquid tin (Gemini), and two-loop NaK/molten salt systems (GPT)—reflect uncertainty about which approach can survive decades of operation. GPT specifically flagged droplet radiators as "high-risk due to contamination concerns," highlighting the intersection of environmental degradation and process-generated contamination as an unresolved challenge.

Why This Matters

Thermal rejection is the enabling constraint for manufacturing throughput. If radiator capacity degrades faster than anticipated, nodes will face thermal throttling that directly reduces daily metal production (10-25 tonnes/day target) and thin-film output (2,000-5,000 m²/day target). A 20% reduction in thermal rejection capacity could force proportional production cuts, extending the 18-24 month replication cycle and undermining the exponential growth strategy central to Phase 2 expansion.

The consequences cascade through multiple dependencies:

• Self-replication timeline: Degraded nodes cannot maintain the 30% capacity allocation for replication components
• Fleet scaling: Slower replication compounds across generations, potentially adding years to swarm completion
• Maintenance burden: If radiators require replacement every 5-10 years instead of lasting 25 years, the fleet must dedicate significant production capacity to replacement panels rather than swarm collectors
• Mass closure targets: Radiator replacement components may require Earth-supplied specialty materials, threatening the <6-10% Earth-supplied mass fraction goal

The recommended approach calls for ≥30% thermal margin and segmented/redundant radiator wings, but these mitigations are sized against unknown degradation rates. Without validated lifetime data, margin sizing is speculative.

Key Considerations

Micrometeoroid flux and impact effects: At 0.9-1.1 AU heliocentric orbit, manufacturing nodes face continuous bombardment. Coolant loop punctures cause immediate capacity loss; cumulative surface pitting degrades emissivity over time. The 12,000+ m² radiator area presents substantial cross-section.

Process contamination sources: Manufacturing operations generate particulates from crushing/refining (the consensus emphasizes strict zoning and electrostatic precipitators), outgassing from thermal processes, and potential coolant leaks. Contamination films on radiator surfaces reduce emissivity and heat rejection efficiency.

Coolant system integrity: Two-loop systems using NaK or molten salts operate at elevated temperatures. Seal degradation, thermal cycling fatigue, and micrometeoroid penetration all threaten loop integrity. Self-sealing coolant loops are recommended but unproven at scale.

Material selection tradeoffs: High-emissivity coatings that maximize thermal performance may be more susceptible to UV degradation or contamination adhesion. Bare metal surfaces are more durable but less efficient.

Inspection and repair constraints: 30+ day autonomous operation requirements mean radiator health monitoring and repair must be automated. Leak detection, isolation, and repair in vacuum present significant robotics challenges.

Research Directions

1. Accelerated micrometeoroid impact testing: Conduct hypervelocity impact campaigns on candidate radiator panel constructions (aluminum honeycomb, carbon-carbon composites, segmented tube designs) using light-gas guns. Characterize puncture thresholds, leak propagation rates, and self-sealing effectiveness for NaK and molten salt coolants.

2. Contamination accumulation modeling: Develop computational models predicting contamination deposition rates on radiator surfaces from manufacturing operations, incorporating electrostatic precipitator efficiency data and vacuum transport physics. Validate against ISS radiator contamination measurements.

3. Long-duration emissivity degradation studies: Deploy radiator material coupons on existing orbital platforms (ISS, commercial stations) for multi-year exposure campaigns. Measure emissivity changes from combined UV exposure, atomic oxygen (for LEO analogs), and simulated contamination films.

4. Self-healing coolant loop prototyping: Design and test autonomous leak detection, isolation, and bypass systems for segmented radiator architectures. Quantify response time, coolant loss before isolation, and capacity degradation from segment loss.

5. Probabilistic lifetime modeling: Integrate micrometeoroid flux models, contamination accumulation rates, and material degradation data into Monte Carlo simulations predicting radiator capacity over 25-year operational envelopes. Identify confidence intervals for thermal margin requirements.