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Reliability block diagram templates

RBD — Earth Observation Payload Chain

Five-year mission reliability for an optical imaging smallsat, chaining a cold-standby computer pair, redundant reaction wheels flown four-of-five and a duplex X-band downlink behind a single-string telescope.

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Optical imaging smallsat — payload to groundMission 43 800 h · 5.00 yr · 15 blocks · 4 redundant arrangements · R 0.833109Telescope optical benchR 0.999650CMOS focal planeR 0.989543parallel · R 0.999282Front-end electronics AR 0.973209Front-end electronics BR 0.973209cold standby · switch 0.980 · R 0.997958Onboard computer AR 0.952962Onboard computer BR 0.9529624 of 5 · R 0.869465Reaction wheel 1R 0.869219Reaction wheel 2R 0.869219Reaction wheel 3R 0.869219Reaction wheel 4R 0.869219Reaction wheel 5R 0.869219Solid state recorderR 0.979195parallel · R 0.998506X-band transmitter AR 0.961347X-band transmitter BR 0.961347X-band antenna + rotaryR 0.993452System reliability0.833109Unreliability0.1669System MTTF125 088 h · 14.3 yrAvailabilityno mttr givenReliability importance — Birnbaum ∂R/∂Rᵢ, with criticality share1Solid state recorder0.850810crit 11%2CMOS focal plane0.841913crit 5.28%3X-band antenna + rotary0.838600crit 3.29%4Telescope optical bench0.833401crit 0.17%5Reaction wheel 10.329186crit 26%6Reaction wheel 20.329186crit 26%7Reaction wheel 30.329186crit 26%8Reaction wheel 40.329186crit 26%+7 more blocks not shownWeakest link: Solid state recorder — R 0.979195, Birnbaum 0.850810, 11% of system failure. Improving this one block moves the system number further than improving any other.Redundancy check: removing any one of the 10 branches makes its own group measurably more likely to fail — the least of them by 229%. Every one of them is earning its place.

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title "Optical imaging smallsat — payload to ground"
mission 43800h                # five years on orbit

# Electronics rates in FIT as the parts list states them; mechanisms in
# failures per hour, because reaction wheels do not fail like transistors.
block telescope "Telescope optical bench"    rate: 8 fit
block detector  "CMOS focal plane"           rate: 240 fit
block feeA      "Front-end electronics A"    rate: 620 fit
block feeB      "Front-end electronics B"    rate: 620 fit
block obcA      "Onboard computer A"         rate: 1100 fit
block obcB      "Onboard computer B"         rate: 1100 fit
block rw1       "Reaction wheel 1"           rate: 3.2e-6 /h
block rw2       "Reaction wheel 2"           rate: 3.2e-6 /h
block rw3       "Reaction wheel 3"           rate: 3.2e-6 /h
block rw4       "Reaction wheel 4"           rate: 3.2e-6 /h
block rw5       "Reaction wheel 5"           rate: 3.2e-6 /h
block ssr       "Solid state recorder"       rate: 480 fit
block txA       "X-band transmitter A"       rate: 900 fit
block txB       "X-band transmitter B"       rate: 900 fit
block antenna   "X-band antenna + rotary"    rate: 150 fit

series {
  telescope
  detector
  parallel { feeA; feeB }
  standby cold { primary: obcA; spare: obcB; switch: 0.98 }
  kofn 4 of 5 { rw1; rw2; rw3; rw4; rw5 }
  ssr
  series { parallel { txA; txB }; antenna }
}