Different classes of missions have different reliability strategies. For critical missions (e.g., human-rated), reliability is paramount, requiring higher quality parts and full redundancy strategies for all critical systems.
Mission Classifications
The table below shows the classes of reliability1:
| Class | Description |
|---|---|
| Experimental | Generally short mission to demonstrate capability or gather data to answer a specific question. Missions in this class are often secondary payloads on a launch vehicle. |
| Operational | Mission to gather critical data or to provide critical services. |
| Human-Rated | Vehicles that must support humans. |
Mission Lifetime and Redundancy Considerations
Refer to Redundancy Strategies for detailed redundancy strategies based on mission lifetime.
Key Considerations
- Redundancy doesn’t protect against design flaws
- Before adding redundant components, consider:
- Extra testing
- Better parts
- More thorough analysis of single-string design
- Watch for reliability of switching mechanisms between redundant components
- System reliability includes deployment time considerations
- Balance needed between:
- Costs/delays for ensuring reliability
- Costs/delays from post-launch failures
Footnotes
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J. R. Wertz and W. J. Larson, “Space Mission Engineering: The New SMAD,” Microcosm Press, 2011, page 400. ↩