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: VEX-T.ASTR-TCN.00349
Issue : 2
Date
Rev. : 0
: 06/02/2004
Page : 12.1
12 RELIABILITY AND REDUNDANCY ARCHITECTURE
The Venus Express S/C architecture is recurring from Mars Express S/C with very few exceptions
(addition of HGA2 X-band only antenna with its associated Diplexer and wave guides). Thus, the
redundancy scheme provides the same Mars Express hardware resources to handle on-board failures
through an autonomous failure management. The redundancy concept is mainly derived from
autonomy requirements, failure tolerance requirements, reuse of Mars Express avionics architecture
and reliability figure. This concept allows Venus Express spacecraft to be fully one-failure tolerant.
12.1 REDUNDANCY REQUIREMENTS
Autonomy
As Venus Express is required to be autonomously one-failure tolerant (decision taking function
without ground intervention on failure/event occurrence), all failures which endanger the Spacecraft
integrity need to be managed on-board. The FDIR function is in charge of failures management using
redundancy resources. Most functions are supported by stand-by redundancies. Hot redundancy and
majority voting are used for critical functions (main bus regulation, reconfiguration module, WD...).
To improve availability (waiting for powering on) hot stand-by redundancies can be programmed for
critical mission phases (Venus orbit insertion manoeuvre).
Failure tolerance
The Venus Express spacecraft is designed to be one-failure tolerant which means that each EEE
function is redunded as a minimum. Specific design rules (segregation, thermal dissipation control,
parts redundancy, etc.) is implemented to avoid failure propagation.
Reuse of Mars Express Avionics architecture
The redundancy architecture has been kept as is because of the numerous existing similarities between
Mars Express and Venus Express in terms of mission, autonomy and failure tolerance constraints.
Reliability figure
Cross-strappings are implemented so as to improve significantly the spacecraft reliability figure or the
operational flexibility, but shall not bring additional risks by increased design complexity.