ARIANE 5 FLIGHT 501 FAILURE GARIMELLA SUDHEER EE 585: Fault Tolerant Computing

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ARIANE 5FLIGHT 501 FAILUREGARIMELLA
SUDHEEREE 585 Fault Tolerant Computing
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THE FAILURE

• General Description
• Weather conditions at launch time were
  acceptable.
• The launch was initiated at 09h 33mn 59s( Local
  Time).
• Nominal behavior of the launcher up to
  H036seconds.
• Failure of the back up Inertial reference system
  followed by failure of actual inertial system.

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ANOMOLIES OBSERVED

• One Major anomaly was gradual development of
  variations in the hydraulic pressure of actuators
  of the main engine nozzle.
• This anomaly was observed at H022 seconds
• These variations had a frequency of approximately
  10Hz.

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ANALYSIS OF FAILURE

• In general flight control system of the Ariane 5
  is of standard design.
• The attitude of the launcher and its movements in
  space are measured by an Inertial Reference
  system (SRI).
• The design of Ariane 5 SRI is practically the
  same as that of an Ariane 4 SRI in particular to
  software.

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ANALYSIS OF FAILURE (CONT)

• Launcher started to disintegrate at H039seconds.
• The disintegration occurred due to software
  exception of On board computer.
• The software exception was caused during
  conversion of 64 bit floating point to 16 bit
  signed integer value.

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COMMENTS

• The primary cause for failure scenario are
  operand error when converting the horizontal bias
  variable BH.
• Lack of protection of this conversion which
  caused the SRI computer to stop.

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OTHER WEAKNESSES

• The review has covered following areas.
• - The design of the electrical system
• - Embedded on board software in subsystem other
  than the Inertial frame of reference system.
• -The on board computer and the flight program
  software

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CONCLUSIONS

• The failure of Ariane 501 was caused by the
  complete loss of guidance and attitude
  information.
• This loss of information was due to
  specifications and design errors in the software
  of inertial reference system.

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REFERENCES

• ARIANE 5 FLIGHT 501 FAILURE
• Report by chairman of enquiry board
• Prof.J.L.LIONS.
• http//www.arianespace.com
• http//www.ima.umn.edu/arnold/disasters/ariane.ht
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