Maintaining a Billion Units: Optimal Depot Spacing for Swarm Operations

When your swarm contains 10 million collectors, maintenance becomes a logistics challenge of unprecedented scale. We built a discrete event simulator to answer: How should maintenance depots be distributed to minimize response time while controlling costs?

The Challenge

At scale, the Dyson swarm faces daunting maintenance requirements:

• 10 million collectors spread across millions of km³
• 2% annual failure rate = 200,000 failures/year
• Response time matters—unrepaired units degrade swarm performance

The depot architecture must balance:

• Response time (closer depots = faster repair)
• Infrastructure cost (more depots = higher investment)
• Fleet utilization (efficient drone deployment)

The Key Finding: 150,000-200,000 km Spacing

Depot spacing of 150,000-200,000 km achieves optimal cost-efficiency.

Depot Spacing	Depots Required	MTTR	Fleet Util	Cost/Mission
50,000 km	2,500+	2 days	60%	$500k
100,000 km	800	4 days	75%	$350k
150,000 km	400	5 days	85%	$280k
200,000 km	250	7 days	88%	$250k
500,000 km	50	15 days	95%	$400k

The sweet spot provides:

• Acceptable mean time to repair (<7 days)
• High fleet utilization (>85%)
• Minimum cost per service mission

Why Dense Spacing Fails

Intuition suggests closer depots = faster repair. But the simulation reveals diminishing returns:

At 50,000 km spacing:

• 2,500+ depots required
• Each depot underutilized (60%)
• Propellant wasted on short hops
• Infrastructure cost dominates

The drones spend more time idle than servicing.

Why Sparse Spacing Fails

At 500,000 km spacing:

• Only 50 depots, but...
• 15-day mean time to repair
• Long transit times waste drone capacity
• Some failures go unserviced

Response time exceeds acceptable limits for swarm performance.

Fleet Sizing at Scale

For a 10 million collector swarm with 2% annual failure rate:

Fleet Component	Count	Purpose
Inspector Drones	20,000	Detection and diagnosis
Servicer Drones	2,000	Repair and replacement
Depots	250-400	Base of operations

Total propellant consumption: 500-1,500 tonnes/year

This is substantial but achievable with ISRU propellant production.

The Logistics Model

Each service mission follows this sequence:

1. Failure detection (inspector patrol)
2. Dispatch servicer from nearest depot
3. Transit to failed unit (Hall-effect thrusters)
4. Repair/replace (cold-gas proximity ops)
5. Return to depot for refuel/rearm

Transit time dominates the cycle. Depot spacing directly determines transit distance.

Propellant Economics

With Hall-effect thrusters at 1,500-2,000 s Isp:

Mission Type	Propellant/Mission	Annual Total
Inspector sortie	50-100 kg	1,000 tonnes
Servicer mission	200-500 kg	400 tonnes
Total	—	1,400 tonnes

At optimized spacing, propellant consumption is minimized while maintaining response time.

Depot Architecture

Each depot (at 150,000 km spacing) requires:

• Drone complement: 50 inspectors, 8 servicers
• Propellant storage: 50-100 tonnes
• ORU inventory: 500-1,000 common spares
• Power: 50-100 kW (solar)
• Communication: Relay to Earth/regional coordinator

Total depot mass: ~500-1,000 tonnes each

The Response Time Distribution

The simulation generates MTTR distributions:

Percentile	Response Time
50th	4 days
90th	8 days
95th	12 days
99th	18 days

95% of failures are addressed within 12 days—acceptable for swarm performance given the 10% graceful degradation tolerance.

Try It Yourself

We've published the interactive simulator so you can explore depot architectures. Adjust spacing, fleet sizes, swarm scale, and failure rates to see how MTTR and costs change.

Methodology

The simulation uses:

• Discrete event simulation with failure generation
• Nearest-depot dispatch algorithm
• Delta-V calculations for transit costs
• 50+ Monte Carlo runs per configuration

Results represent relative comparisons between architectures.

Implications for Phase 2

1. Plan for ~300 Depots

This provides coverage for 10M+ collectors with acceptable response time.

2. Size Drone Fleet at 20,000+ Inspectors

Early detection is critical—invest in inspection capacity.

3. Budget 1,500 tonnes/year Propellant

ISRU must supply maintenance fleet propellant at scale.

4. Standardize ORUs Across Fleet

Common replacement units simplify inventory and reduce logistics complexity.

What's Next

This research answers RQ-2-7, providing validated depot architecture for Phase 2 maintenance operations. The 150,000-200,000 km spacing becomes the baseline for infrastructure planning.

Remaining work:

• Propellant supply chain architecture
• Failure mode spatial distribution analysis
• Fleet degradation scenario modeling

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Research Question: RQ-2-7: Optimal depot spacing and logistics architecture

Interactive Tool: Depot Logistics Simulator