Reliability Assessment

Applicable Phases

• Primary: Phase B (preliminary FMECA, radiation assessment), Phase C (detailed FMECA, parts selection)
• Supporting: Phase A (risk identification), Phase D (anomaly investigation)

Analysis Domains

1. Reliability Modeling

• Reliability Block Diagrams (RBD): $R_{sys} = \prod R_i$ (series) or $R_{sys} = 1 - \prod(1-R_i)$ (parallel/redundant).
• Failure rates ($\lambda$): Use MIL-HDBK-217 or FIDES for initial estimates. Actual rates from manufacturer data where available.
• MTTF/MTBF: $MTTF = 1/\lambda$ for exponential distribution.
• Redundancy: Identify single points of failure (SPOFs). Recommend cold, warm, or hot redundancy where criticality warrants it.

2. Radiation Assessment

• Total Ionizing Dose (TID): Estimate based on orbit, duration, and shielding. Use AP-8/AE-8 or AP-9/AE-9 models for trapped radiation.
• Single Event Effects (SEE): SEU (bit flip — recoverable), SEL (latch-up — potentially destructive), SEB (burnout — catastrophic).
• Shielding: Aluminum equivalent thickness. Typical spacecraft provide 3-10 mm Al shielding. Spot shielding for sensitive parts.
• Parts derating: Ensure components operate below maximum rated values (typically 60-80% derating for voltage, current, power).

3. FMECA

• Identification: List failure modes for each subsystem/component.
• Effects: What happens at component, subsystem, and system level?
• Criticality: Severity (1-4) × Probability (A-E) matrix.
• Mitigation: Hardware redundancy, software FDIR, operational procedures.
• Feed to hazard-analysis: Failure modes become "Causes" in the top-down hazard reports.

4. Parts & Materials

• Screening: Space-grade (expensive, radiation-hard, long lead) vs. COTS (cheap, needs testing/shielding, shorter lead).
• Obsolescence: Flag parts with end-of-life risk over mission development timeline.
• Outgassing: Materials near sensitive surfaces must meet ASTM E595 (TML < 1.0%, CVCM < 0.1%).

Output Format

1. Risk Assessment Report (risk_assessment.md): RBD results, TID estimate, 5×5 Criticality Matrix, SPOF list.
2. Probability of Success: Mission reliability estimate (e.g., "93% probability of completing 2-year primary mission").
3. FMECA Table: Failure modes, effects, severity, probability, mitigation.

Interface

• Reads from: /requirements/, /analysis/mission-analysis-specialist/ (orbit for radiation environment)
• Writes to: /analysis/reliability-assessment/
• Consumed by: hazard-analysis (failure modes as causes), flight-software-architect (rad-hard requirements), systems-engineering-assessment (risk summary)