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Reliability block diagram templates

RBD — GEO Ku-Band Payload

Ten-year design life of a geostationary communications payload: cold-standby receiver, 3-of-4 travelling-wave tube amplifiers, output multiplexer and a cross-strapped TT&C transponder pair.

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GEO communications payload — Ku-band chainMission 87 600 h · 10.0 yr · 11 blocks · 3 redundant arrangements · R 0.703357Spacecraft bus (power + AOCS)R 0.884582cold standby · switch 0.998 · R 0.970558Receiver, primaryR 0.768896Receiver, cold spareR 0.7688963 of 4 · R 0.876238TWTA 1R 0.839289TWTA 2R 0.839289TWTA 3R 0.839289TWTA 4R 0.839289Output multiplexerR 0.965567Shaped-beam antennaR 0.999000parallel · R 0.969274TT&C transponder AR 0.824713TT&C transponder BR 0.824713System reliability0.703357Unreliability0.2966System MTTF166 816 h · 19.0 yrAvailabilityno mttr givenReliability importance — Birnbaum ∂R/∂Rᵢ, with criticality share1Spacecraft bus (power + AOCS)0.795129crit 31%2Output multiplexer0.728440crit 8.46%3Shaped-beam antenna0.704061crit 0.24%4TWTA 10.272611crit 15%5TWTA 20.272611crit 15%6TWTA 30.272611crit 15%7TWTA 40.272611crit 15%8Receiver, primary0.168523crit 7.19%+3 more blocks not shownWeakest link: Spacecraft bus (power + AOCS) — R 0.884582, Birnbaum 0.795129, 31% of system failure. Improving this one block moves the system number further than improving any other.Redundancy check: removing any one of the 7 branches makes its own group measurably more likely to fail — the least of them by 230%. Every one of them is earning its place.

Make it your own.

title "GEO communications payload — Ku-band chain"
mission 87600h               # ten-year design life

block bus   "Spacecraft bus (power + AOCS)" rate: 1.4e-6 /h
block rcvr1 "Receiver, primary"             rate: 3.0e-6 /h
block rcvr2 "Receiver, cold spare"          rate: 3.0e-6 /h
block twta1 "TWTA 1"                        rate: 2.0e-6 /h
block twta2 "TWTA 2"                        rate: 2.0e-6 /h
block twta3 "TWTA 3"                        rate: 2.0e-6 /h
block twta4 "TWTA 4"                        rate: 2.0e-6 /h
block ompx  "Output multiplexer"            rate: 4.0e-7 /h
block ant   "Shaped-beam antenna"           r: 0.999
block ttcA  "TT&C transponder A"            rate: 2.2e-6 /h
block ttcB  "TT&C transponder B"            rate: 2.2e-6 /h

# A cold spare receiver does not age on the shelf; the switch itself is the
# thing that can let you down, hence the explicit switch reliability.
series {
  bus
  standby cold { primary: rcvr1; spare: rcvr2; switch: 0.998 }
  kofn 3 of 4 { twta1; twta2; twta3; twta4 }
  ompx
  ant
  parallel { ttcA; ttcB }
}