Reusability Analysis Skill

Read CONVENTIONS.md at the repo root before proceeding.

This skill evaluates whether reusing a vehicle element is economically and technically viable. Reusability is the single largest cost lever in spaceflight — but only if the recovery penalties and refurbishment costs don't erase the savings.

Before You Begin

Ask the user (if not already known):

1. What element is being reused? (First stage booster, upper stage, fairing, spacecraft, capsule)
2. Recovery method? (Propulsive landing, parachute + ocean recovery, parachute + land, glide-back, mid-air capture)
3. Target reuse count? (1x = expendable baseline, 10x = Falcon 9 class, 100x+ = Starship ambition)
4. Flight rate? (Launches per year — amortization only works above a minimum cadence)
5. What design phase?

Applicable Phases

• Primary: Phase A (reusability vs. expendable trade), Phase B (recovery system preliminary design)
• Supporting: Phase C (detailed refurbishment planning), Phase D (operational reuse tracking)

Analysis Domains

1. Recovery System Sizing

Propulsive Landing

• Landing propellant reserve: Typically 10-15% of stage propellant for boostback + entry burn + landing burn.
• Performance penalty: Payload reduction = $\Delta m_{payload} \approx m_{prop,landing} \cdot (1 + k_{structural})$ where $k_{structural}$ accounts for landing legs, grid fins, and additional avionics.
• Reference: Falcon 9 loses ~30-40% payload to LEO for RTLS, ~15-20% for ASDS (downrange landing).
• Landing hardware mass: Legs (1-3% of stage dry mass), grid fins (0.5-1%), additional avionics and sensors.

Parachute / Splashdown

• Parachute system mass: Typically 1-3% of recovered mass.
• Salt water exposure: Drives refurbishment scope — engines, avionics, and structures all affected.
• Recovery fleet: Ship + crane + logistics per recovery (operational cost).

Fairing Recovery

• Parafoil + GPS guidance: Fairing halves, ~1000 kg each.
• Economic value: Each fairing costs $5-6M; recovery saves ~$3-4M per flight after capture costs.

2. Reuse Degradation Modeling

Components degrade with each flight cycle:

System	Degradation Driver	Typical Limit	Inspection
Engines	Turbopump wear, chamber erosion, injector coking	10-100+ flights (depends on engine)	Borescope, flow testing
Structures	Fatigue (launch + landing loads), thermal cycling	Fatigue life analysis per MIL-STD	NDT (UT, X-ray)
Thermal Protection	Ablation, tile damage, heat shield erosion	Per-flight mass loss tracking	Visual + thickness gauge
Avionics	Vibration fatigue, connector wear	Typically not the limiter	Functional test
Tanks	Pressure cycling, cryo-cycling fatigue	COPV cycle life (design dependent)	Proof test, acoustic emission

3. Refurbishment Cost Model

• Level 0 — Inspect & Fly: Visual inspection, functional test, propellant reload. (Target: <5% of new-build cost)
• Level 1 — Minor Refurb: Replace consumables (igniters, seals, pyros), touch-up coatings. (Target: 5-15%)
• Level 2 — Major Refurb: Engine teardown/rebuild, structural repair, avionics replacement. (Target: 15-40%)
• Level 3 — Overhaul: Comparable to new build — if you're here regularly, reuse isn't saving money.
• Turnaround time: Days (inspect & fly) to months (major refurb). This directly limits flight rate.

4. Flight-Rate Economics

The break-even calculation:

• Expendable cost per flight: $C_{exp}$
• Reusable cost per flight: $C_{reuse} = (C_{vehicle} / N_{flights}) + C_{refurb} + C_{recovery} + C_{ops}$
• Break-even flight count: $N_{break} = C_{vehicle} / (C_{exp} - C_{refurb} - C_{recovery} - C_{ops})$
• Payload penalty cost: If reuse reduces payload, some missions need a larger (more expensive) vehicle — factor this in.

Key insight: Reuse only wins if $N_{flights}$ exceeds $N_{break}$ AND the flight rate is high enough to amortize fixed costs (facilities, recovery fleet, refurb workforce).

5. Design-for-Reuse Checklist

• Landing load cases added to structural design
• Engine designed for multiple ignition cycles (bearing life, seal life)
• TPS designed for multi-flight thermal cycling
• Avionics designed for rapid functional test (automatable)
• Propellant system designed for rapid drain/purge/reload
• Access panels for inspection without extensive disassembly
• Data recording (flight loads, temperatures) to support health monitoring

Output Format

1. Reusability Trade Report (reusability_report.md): Expendable vs. reusable comparison with performance penalty, break-even analysis, and economic model.
2. Recovery System Summary: Hardware mass, propellant reserves, and mission impact.
3. Refurbishment Plan: Per-flight and periodic maintenance requirements.
4. 🟢 / 🟡 / 🔴 status: Economic viability at projected flight rate.

Interface

• Reads from: /requirements/, /analysis/propulsion-assessment/ (engine specs, propellant), /analysis/structural-assessment/ (fatigue life), /analysis/cost-modeling/ (expendable baseline cost)
• Writes to: /analysis/reusability-analysis/
• Consumed by: cost-modeling (reuse economics), trade-study-manager (reuse as architecture option), systems-engineering-assessment (mass/performance impact)