class_2 - Software Engineering 3156 Fall 2001 Section 1...

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Software Engineering 3156 Fall 2001 Section 1 10-Sep-01 Class #2: Overview Phil Gross
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2 Administrivia HW0 = questionnaire Fabulous new web site Policy about people who don’t meet the requirements
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3 Case Study: Ariane 501 Next-generation launch vehicle Successor to the Ariane 4 Prestige project for ESA Maiden flight: June 4 th 1996
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4 The System Inertial Reference System What’s my position, velocity, and acceleration? Critical, obviously Dual redundant Calibrated on launch pad Largely carried over from Ariane 4 recalibration routine allowed to continue running for 40 sec after launch
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5 The Problems Recal routine never used after launch, but still active One step in recal converted floating point value of horizontal velocity to integer Ada automatically throws an exception if data conversion is out of bounds If exception not handled, IRS returned diagnostic data instead of position/velocity info
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6 The Situation Perfect launch Starts flying much faster than Ariane 4 Horizontal component goes out of bounds for integer conversion Both IRSs switch to diagnostic mode Control system interprets diagnostic data as very weird orientation And attempts to correct it…
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7 Ariane 501 Go Boom
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8 Postmortem Recal routine had no business being active after launch Horizontal velocity parameter conversion was deliberately allowed to be unchecked Software had never been tested with actual flight parameters Problem easily reproduced in test environment after the fact
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9 At Least It Was Pretty
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10 Extra Case Study Bug Report This is an actual e-mail I received over the
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class_2 - Software Engineering 3156 Fall 2001 Section 1...

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