NEPTUNE power subsystem

1. NEPTUNE power subsystem Progress and Plans April 2003 Harold Kirkham

2. Presentation outline • Progress review • Converter • Mission Assurance • Delivery system • Documentation • Plans

5. DC-DC Converter DC-DC Converter LOAD DC-DC Converter DC-DC Converter Progress: Converter • All operating principles demonstrated • Efficiency and Voltage Regulation are excellent • Current is evenly shared by parallel stages • Voltage is evenly divided by series stages

6. Progress: Converter Efficiency

7. Progress: Converter Regulation

8. Mission Assurance • Four aspects: • Converter • Node Distribution System • Delivery System • Communications

9. Mission Assurance: Converter • Converter stack MTBF estimated: 40 years • Assume worst-case: failure takes out stack • Assume cold-standby redundancy • Assume 30 year NEPTUNE lifetime • Observatory may need a few replacements • Assume substring failure is not fatal • Converter power de-rated by 17% • Observatory may never need a replacement • The Message is: Don’t worry – BE HAPPY!

10. Mission Assurance: Node Distribution • Distribution system power at 400 and 48 V • Assume 400-V source is solidly available • Assume 48-V COTS converters • Assume COTS switches • This is so simple, we have deferred the design • BOTE cost estimates done by JPL & UW • JPL cost: $2,000,000 • UW cost: $250,000

11. JPL assumes Hardware handled by certified people only Complete paper trail for all activities Extensive testing, with tests traceable back Environment complies with ESD and contamination rules All handling requires multiple personnel Mission Assurance: Node Distribution • UW assumes • Hardware handled as needed • Marginal paper trail • Some testing

12. Mission Assurance: Node Distribution • The difference between these numbers is one of culture • The two cost estimates are equally valid • Neither is “right” or “wrong” • The product of the work is different, however • You pay for what you get • Is there a middle ground?

13. Mission Assurance: Delivery System • Triggered by concern over converter reliability, we have devised a “Version 2” • The original motivation may not be valid, but the new design brings major benefits • The biggest benefit of Version 2 is that node failures (power supply or comm failure) do not affect the backbone • This segregation of function leads to better observatory availability

14. How does Version 2 work?

15. Component availability • Zeners, qualified to 2A, preliminary study done for 10A upgrade • Capacitors, qualified • Latching relay, similar to qualified, limited re-qualification needed • Resistors, similar to part in qualification • Bridge, qualified • Controller, space qualified part may be suitable, limited development, or control by analog electronics (qualified)

16. High reliability Parts are qualified or low development cost Low component count Low power consumption Switching only at low power Segregated functionality Better observatory availability Can use single conductor cable, BU to Node Cost savings Version 2 power sub-system Pros and Cons • BU requires a ground • Controllability reduced • Switches cannot be remotely operated

17. Progress: Documentation Project Configuration Configuration Requirements Document Verification Plan Documentation Plan ICD Management PMACS Management Plan Plan System Description Documents Operations Concept Doc Deployment Vessel ICD Test Plan Protection Reports and Minutes Power Project History Converter NEPTUNE level Power Subsystem level

18. Progress: Documentation • All key documents started and on web site • Concept of Operations (Rev 5) • Test Plan (Initial) • Converter (3 files) • PMACS (17 files) • Assorted trade-offs • CoDR docs (37 files) • Total number of files ~400