Requirements Definitions For Discussion

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Requirements DefinitionsFor Discussion

• Jordan P. Evans
• September 26-28, 2005

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Requirements Definition and Semantics

• A Requirement is a communication between the
  users (e.g. the science community) and the
  implementers (e.g. project) about what the
  Mission and Systems must do to satisfy the
  mission objective(s)
• Semantics
• Baseline Requirement
• a BASELINE REQUIREMENT is defined as a
  specification of a condition, parameter, or
  capability with which the System Design must be
  compliant, verifiable, and have a demonstrated
  achievement during the mission
• Goal
• a GOAL is a requirement, except that compliance,
  verification, and achievement do not have a
  commitment
• a GOAL is tracked so if resources/capabilities
  allow, better performance may be achieved
• Minimum Requirement
• a MINIMUM REQUIREMENT is defined as the minimum
  performance floor acceptable for maturing the
  mission
• in the projects quest to fulfill the
  REQUIREMENTS, descopes may be necessary, but only
  down to the levels defined as MINIMUM
  REQUIREMENTS
• Baseline Requirements, Goals, and Minimum
  Requirements are always denoted by use of the
  word shall
• Mission Success Criteria are NOT Requirements
  (Please see later chart)

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Verification Implications

• Baseline Requirements
• Baseline Requirements are verified using some
  combination of the project-accepted verification
  methods
• These are typically Analysis, Test,
  Demonstration, and Inspection
• Goals
• Goals are not required to be verified, as there
  is no commitment to by the project to meet them
• Performance is reported against the goals based
  on analysis or extrapolation of test results
• When the stated performance drops below the value
  defined as a goal, the project may choose to
  expend resources to improve the performance but
  the expenditure is not required
• Minimum Requirements
• Minimum Requirements are not designed to, and
  therefore are not directly verified
• The value represented by a Minimum Requirement
  may be verified If a Requirement for the mission
  is descoped down to the Minimum Requirement
  level

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Mission Success Criteria

• Mission Success Criteria are NOT Requirements
  and, therefore, are not used to control the
  satisfaction of mission objectives within the
  project
• Mission Success Criteria may be defined in the
  PIP and can be used to broadly measure the
  effectiveness of the mission post-launch
• These are what the Washington Post or Los Angeles
  Times will use to judge the success of the
  project
• These are not captured in the Level-1
  requirements (the way Baseline and Minimum
  requirements are)
• We need to be careful with terminology here
• The old OSS Handbook defined Baseline Mission
  Criteria and Minimum Mission Criteria in a
  manner that is completely consistent with our
  Baseline Requirements and Minimum
  Requirements
• It is possible (and likely) that the LISA
  Post-Launch Success Criteria will be equal to
  our Level-1 definition of Minimum Requirements

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Backup Charts
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Requirements Architecture - Context for the SRD
HQ Level Requirements
Mission Requirements Document
Mission Assurance Rqmts Doc
Science Requirements Document
Flight-Ground ICD
Launch Vehicle ICD
System Requirements Document
Environmental Requirements Document
S/C-LOCS, S/C-LIMAS, LOCS-LIMAS, etc. ICDs
Ground Segment Requirements
Science Data Processing Segment Requirement
Flight System and Software Requirements
MOS Subsystem Requirements
LOCS System Requirements
S/C Bus System Requirements
LIMAS System Requirements
Propulsion Module Requirements
Subsystem Requirements
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Requirement Architecture