X-Ray Calorimeter ~ Concept Presentation ~

1. X-Ray Calorimeter ~ Concept Presentation ~ Reliability Aron Brall Luis Gallo Dec 17, 2011

2. Reliability Requirements • Success criteria • Perform Instrument function for 3 year mission with 90% probability of success with minimum level of redundancy • Evaluate Reliability for added redundancy

3. Reliability Requirements - 2 • Reliability Assurance • Designs are validated with appropriate Reliability Analyses – FTA, FMEA, Parts Stress Analysis, PRA, etc. • Designs meet NASA and GSFC specifications including: • EEE-INST-002 • GEVS (GSFC-STD-7000: General Environmental Verification Standard) • GSFC Gold Rules (GSFC-STD-1000)

4. Reliability Assumptions - 1 • Switch to Cold Standby Redundant functions manually controlled by Mission Operations • Component lifetimes follow exponential distribution except Mechanism and Motor Bearings and gears which are modeled using Weibulldistribution • The following are considered non-credible single point failures SPF: • Structural and non-moving mechanical components • Short or open on power bus • Software and procedural failures are not included in the analysis • Flight Software can be updated during operation and is modeled as reliability of 1

5. Reliability Assumptions - 2 • Exact models were used to determine subsystem reliabilities • Cold Standby Redundant exponential models for: • Cryocooler Electronics • Filter Wheel mechanism electronics • Hot Redundancy exponential models for • Detectors and Detector Electronics • Heater circuits • X-Ray Calibration Source • ADR Heat Switch circuit • Aperture Door Actuator • Binomial exponential models for k of n subsystems • Calorimeter Electronics • Detectors • Redundant Cryocooler Failure Rate is average of 4 quoted designs received by customer; Single String is based on one quoted design

6. Reliability Assumptions - 3 • Detector Configuration • PSA section of detector requires all pixels to function for instrument performance • 6 of 7 or 4 of 5 Detector Pixels per row per half necessary for instrument performance • 6 of 7 Hydra Pixels per row per half necessary for instrument performance • 35 of 36 rows of detector pixels and 19 of 20 rows of Hydra pixels necessary for instrument performance • Processing in two halves – one half necessary for instrument performance • Duty Cycles • Survival Heaters – 10% • Active Heaters – 70% • Mechanisms – 1% • All other components – 100% • Radiation • All components are assumed to be appropriately Rad Hard (or protected) for the L2 environment

7. Redundant Elements • Electronics • Detector Electronics w/ LVPS • SpaceCube Processors • Calibration Source • Cryogenics • Redundant Cryocooler Electronics • Heaters, thermistors, and heater control circuits for ADR • Mechanisms • Motor windings; feedback devices; drive circuits • Thermal System • Heaters – 1 primary and 1 secondary per heater circuit • Thermostats – 2 primary and 2 secondary per heater circuit • Thermistors – 1 primary and 1 standby for operational heater control circuit

8. X-Ray Calorimeter Reliability Block Diagram (RBD) Note: There are internal redundancies in Detector, Cryogenics, Mechanisms and Thermal Blocks

9. X-Ray Calorimeter Reliability Block Diagram (Functional Redundancy)

10. Reliability Results

11. Reliability Results w/MM* Analysis Note: This doesn’t include the post-study-week MM analysis on damage to the optical train.

12. Reliability Results w/Electrical Redundancy Functional Electrical Redundancy, Cold Standby MEB, Functionally redundant FEE, DEEP

13. Reliability Results w/Full Redundancy Full Redundancy, Cold Standby MEB, FEE, DEEP, Redundant Thermal

14. Conclusions and Recommendations • Instrument meets requirement of 90% even including MM Strike of functional hardware (exception – MM strike to optical train). • Use loose fit bearings on Filter Wheel actuator and mechanism to preclude mechanism seizing (only credible SPF) • Assure all assemblies (in-house and out-of-house) have Parts Stress Analysis (PSA) and Failure Modes and Effects Analysis (FMEA) performed to assure compliance with derating and fault tolerance requirements • Perform Probabilistic Risk Analysis (PRA) early in the program to identify high risk items and assure estimated reliability is met by designs • Perform Common Cause Analysis to Assure Redundancy is adequate • Perform Worst Case Analysis (WCA) to assure part functionality over entire mission duration • Use High Reliability Components wherever possible • “Non-credible” Single Point Failures should be addressed with Probabilistic Risk Analysis, Failure Modes and Effects Analysis, and detailed Failure Modeling to assure they are truly “non-credible”

15. Backup Information

16. Modeling Assumptions and Other Information • Detector Pixel modeled as photodiode at cold temperature • SQUID modeled as 20,000 gate ASIC at cold temperature • ADR is not considered high risk for Reliability due to its simple design and lack of credible failure modes at low temperature and 3 year duration. • Reliability Model does not address Radiation related failures. Radiation Engineering would have to provide probabilities of cosmic rays or other significant radiation striking vulnerable components. • Adding redundant cold standby MEB is a “no brainer” for gain in instrument reliability at relatively little cost in $ and mass, which reduces requirements on Spacecraft Bus from 0.95 Ps to 0.90 Ps which may have significant reduction in cost.