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Statistical Software Engineering (1996) / Chapter Skim
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Case Study: NASA Space Shuttle Flight Control Software
Pages 9-12

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From page 9...
... Throughout the program, the prevailing management philosophy has been that quality must be built into software by using software reliability engineering methodologies. These methodologies are necessarily dependent on the ability to manage, control, measure, and analyze the software using descriptive data collected specifically for tracking and statistical analysis.
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From page 10...
... However, the requirements of the flight missions evolved to include increased operational capability and maintenance flexibility. Among the shuttle program enhancements that changed the flight control system requirements were changes in payload manifest capabilities and main engine control design, crew enhancements, addition of an experimental autopilot for orbiting, system improvements, abort enhancements, provisions for extended landing sites, and hardware platform changes.
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From page 11...
... In addition, the CM system includes data detailing scenarios for possible failures and the probability of their occurrence, user response procedures, the severity of the failures, the explicit software version and specific lines of code involved, the reasons for no previous detection, how long the fault had existed, and the repair or resolution. Although these data seem abundant, it is important to acknowledge their time dependence, because the software system they describe is subject to constant ``churn.7' Over the years, the CM system for the space shuttle program has evolved into a common, minimum set of data that must be retained regarding every fault that is recognized anywhere in the life cycle, including faults found by inspections before software is actually built.
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From page 12...
... Safely Certification The dependability of safety-critical software cannot be based merely on testing the software, counting and repairing the faults, and conducting "live tests" on shuttle missions. Testing of software for many, many years, much longer than its life cycle, would be required in order to demonstrate software failure probability levels of 10-7 or 10-9 per operational hour.
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Key Terms

  • shuttle flight
  • flight control
  • shuttle program
  • flight software
  • software development

  • control software
  • process improvement
  • main engine
  • fault density
  • software engineering

  • descriptive data
  • shuttle software
  • engineering methodologies
  • systematically collected
  • increased operational

  • shuttle computer
  • guard actively
  • improving process
  • basic flight
  • various ages

  • minimum set
  • configuration management
  • providing guidance
  • critical implications
  • include increased

  • complete integrated
  • maintains approximately
  • flight activities
  • incorrect configuration
  • control design


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