Ariane V update

[Ken Garlington <garlingtonke@lmtas.lmco.com>]

Aviation Week and Space Technology has an article on the Ariane V 
failure. It quotes Jean-Michel Desobeau, director of engineering at 
Arianespace as saying:

"The on-board computer received or self-generated bad attitude
information. It thought the vehicle was at the wrong attitude, commanded 
the SRB nozzles to compensate, and they executed it."

Other items:

  o  The flight is called a "qualification" flight, which sounds to me
     like it was part of the test program and not really a "production"
     flight.

  o  Although the telemetry data from the inertial units showed no
     failures, the output path to telemetry from the IMUs is different
     than the one to the on-board computers, so "there is a chance
     the computers were receiving different information than the
     telemetry."

  o  The on-board computers are dual-redundant (which amazed me; I would
     have expected triplex at least). The June 12, 1995 edition of AW&ST
     apparently had an article on some problems encountered with the
     development of the fail-operational [!] fault detection algorithms
     between the two computers, requiring extra manpower to solve.

  o  "The computers are more powerful than the single [non-redundant!]
     one in the Ariane 4, but they use the same general logic."

  o  The on-board computers have a "common sense" algorithms to fault
     isolate between the two inertial units. [In my experience, these
     algorithms are not easy to do right.]

-- 
LMTAS - "Our Brand Means Quality"