Development of New GPS Performance Standards

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Development of New GPS Performance Standards
Lt. Col. John AntonMaj. Robert HessinMr. Joe
SappMr. Rob Conley
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Purpose

• The GPS SPS Performance Standard defines the
  levels of performance the U.S. Government commits
  to provide civil GPS users

A Commitment of Service
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Background

• Last revision published in 1995
• DOT requested DoD to update
• OASD(C3I) requested HQ USAF/XO lead effort
• New standards must be supportable with the
  current baseline system

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Status

• Completed extensive Air Force coordination
• Conducted informal coordination with civil
  agencies through DOT
• Turned over to OASD(C3I) for final DoD POS/NAV
  Executive Committee coordination

Signature expected this fall. Document still
DRAFT, and standards could be changed during
final coordination
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Supporting Analysis

• Sustainable performance standards
• Performance variations
• GPS sustainment risk
• Operational implementation

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Overview of GPS SPS Performance Standards

• Main body -- The performance standards
• Constellation management
• Service availability
• Service reliability
• Accuracy
• Status and problem reporting
• Appendix A -- Documented historical performance
  and supporting analysis. For information only!

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Constellation Management

• 24-satellite constellation
• Nominal orbital slots
• Tolerances

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Service Availability

• 24 operational sats available with .95
  probability (averaged over any day)
• At least 21 sats in slots, healthy, with .98
  probability (yearly averaged)

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Service Availability (cont)
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Service Reliability
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Accuracy
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GPS Status and Problem Reporting

• U.S. Government provides notification of changes
• That affect the service provided
• If it anticipates a problem in supporting the
  performance standards
• At least 48 hours prior for scheduled events. As
  soon as possible for unscheduled outages
• Via NANUs to NOTAM and Coast Guard LNM systems

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Evolution of SPS Performance Standard Values
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Monitoring Capabilities and Limitations

• Control segment monitors PPS, not SPS
• Gaps in monitor station visibility
• Users care whether standards are met
• Operators care whether they have the tools to do
  the job well

We will assess ways to improve monitoring and
measurement capabilities
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Conclusion

• The AF, DoD, and U.S. Government are committed to
  being good stewards of GPS