NEPTUNE power subsystem

transcript

Progress and Plans

April 2003

Harold Kirkham

Presentation outline

• Progress review– Converter– Mission Assurance – Delivery system– Documentation

• Plans

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

DC-DCConverter

Progress: Converter Efficiency

0 100 200 300 400 500 600 700 800 900

Output Power (W)

Progress: Converter Regulation

-0.050%

-0.040%

-0.030%

-0.020%

-0.010%

0.000%

0.010%

0.020%

0.030%

0 100 200 300 400 500 600 700 800 900-0.050%

-0.040%

-0.030%

-0.020%

-0.010%

0.000%

0.010%

0.020%

0.030%

0 100 200 300 400 500 600 700 800 900

Output Power (W)

Mission Assurance

• Four aspects:– Converter– Node Distribution System– Delivery System– Communications

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!

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

• 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

• UW assumes– Hardware handled as

needed– Marginal paper trail

– Some testing

• 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?

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

How does Version 2 work?

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)

Version 2 power sub-system Pros and Cons

• 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

• BU requires a ground• Controllability reduced

– Switches cannot be remotely operated

Progress: Documentation

ConfigurationManagement

ProjectDocumentation Plan

RequirementsDocument

DeploymentVessel ICD

OperationsConcept Doc

SystemDescriptionDocuments

VerificationPlan ICD

Test Plan

Reportsand

Minutes

Power ProjectHistory

Protection

Converter

NEPTUNE level Power Subsystem level

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