The goal of software engineering is to offer methods, techniques and tools that make it possible to

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• The goal of software engineering is to offer
  methods, techniques and tools that make it
  possible to develop
• the right software, delivered defect free, on
  time and on cost, every time !!
• (Software Engineering Institute).

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The cost of finding, and fixing, a defect
Pressman, 92
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The New and Old Challenge

• Flight Software Maintenance

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• the right software, delivered defect free, on
  time and on cost, every time !!

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Why do we have flight software at all?

• To provide flexibility to late breaking changes

• To allow correction for unexpected environmental
  issues

• To allow correction for degrading hardware in
  flight

The right software needs to do many things
which cannot be specified up front!
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What is a defect anyway?

• a deviation from the specification?

• a specification error?

• a mismatch at an interface?

How many do we have now?

• cannot be measured

• cannot be analysed

• out of scope of software engineers

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the right software, delivered defect free, on
time and on cost, every time !!
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The cost of finding, and fixing, a defect
Costs in operational phase inflated by number of
deployed units and recall effort we have only
single or few satellites !!

• Usual cost, including diagnosis, implementation
  validation 10-20 days

Much more important What may be the cost of
not fixing a problem ?
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Philosophy
Specification
Implementation
Validation
Operation
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Philosophy
Accept that defects exist Software is no better
then hardware It has no redundancy But - we can
repair it !!
Specification
Implementation
Validation
Operation
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Software is a subsystem of its own Prepare to
operate it that way Specify operational monitor
controlof the software, not only of its
functions
Philosophy
Specification
Implementation
Validation
Operation
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Philosophy
Add a margin for flexibility Choose an
appropriate software architecture Plan for
non-stop running, replace portions Provide good
diagnostics / post-mortems
Specification
Implementation
Validation
Operation
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Philosophy
Specification
Validate in flight envelope Ensure it works for
flight scenarios Do not validate against
specifications Good enough is good enough
Implementation
Validation
Operation
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Philosophy
Specification
Implementation
Prepare for maintenance operations Tools
procedures for corrections Regression test
capability In house expertise
Validation
Operation
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