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Agenda

Surveillance and Broadcast Services GPS Constellations and Support for Separation Standards: National Space Based Positioning, Navigation and Timing (PNT) Advisory Board. Agenda. Objective GPS Constellation Performance Current Separation Standards

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Agenda

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  1. Surveillance and Broadcast Services GPS Constellations and Support for Separation Standards: National Space Based Positioning, Navigation and Timing (PNT) Advisory Board

  2. Agenda • Objective • GPS Constellation Performance • Current Separation Standards • Required Integrity to Support Separation Standards • Current Specified 24 Satellite Constellation • Future 24 Satellite Constellation • 27/30 Satellite Constellations • Conclusions • Next Steps

  3. Separation Standards Analysis Objective • Determine the GPS constellation configuration that support various separation standards for the En Route and Terminal domains

  4. GPS Constellation Performance • The GPS Standard Positioning Service (SPS) Performance Standard defines the minimum requirements for GPS performance • In support of the service availability standard, 24 operational satellites must be available on orbit with 0.95 probability (averaged over any day) • At least 21 satellites in the 24 nominal plane/slot positions must be set healthy and transmitting a navigation signal with 0.98 probability (yearly averaged) • Achieved 95% Global Accuracy of 13m with a worst case 95% Site Accuracy of 36m • GPS performance has historically exceeded the minimum SPS requirement • Current Constellation has 31 satellites that are operational (28 usable as of August 29, 2007) • Achieved 95% Global Accuracy of 4m with a worst case 95% Site Accuracy of 6m

  5. GPS Constellation Performance • Availability of a defined level of integrity is basis for detemining GPS Constellation ability to support separation standards • Integrity in ADS-B is termed Navigational Integrity Category (NIC) • GPS terminology refers to integrity Horizontal Protection Limit (HPL) • Analysis for GPS support of providing a separation standard will be based on the availability of the minimum integrity value necessary for a separation minima • Analysis conducted by MITRE

  6. Current Separation Standards • Analyzed all Terminal separation cases • 5nm En Route • 3nm Terminal • 2.5nm Terminal on approach • 1.5nm Terminal on staggered dependent approaches • 4,300 feet on independent parallel approaches

  7. Required Integrity to Support Separation Standards • MITRE Close Approach Probability Model is basis of determining integrity values that support a defined separation standard • Calculates probability of close approach (aircraft actually separated by 200ft or less) when aircraft are displayed with a defined separation • Compares the relative performance, using CAP as a metric, of ADS-B with today’s radar separation • Determines the minimum Navigational Accuracy Category and NIC value required from ADS-B avionics to support a defined separation minima

  8. MITRE Model Terminal Results: Summary • MSSR Radar Cross Range Error Compared to NIC/NAC and NUC values of ADS-B that provide equivalent Close Approach Probability (CAP) of 10-12 to that of radar • 10-12 probability selection based on ICAO acceptance of this risk value for comparative assessment of extending Mode S radar range to 250NM

  9. MITRE CAP Model Analysis Results • Model estimates the probability of separation loss (separation of <= 200 feet) with an apparent display separation less than or equal to the separation minima • Determination of minimum NIC/NAC for Terminal and En Route Separation Standards • NIC of at least 7 and NAC of at least 8 are required for ADS-B to have equivalent or lower CAP risk than radar - Driving Requirement is Independent Parallel Approach Separation • Radar / ADS-B separation case also drives ADS-B NIC/NAC selection NIC/NACp Requirements for Close Approach Probability of 10-12 Equivalence

  10. NIC Relationship to Containment Radius (Rc) • Containment Radius is the radius within which a reported position is assured to lie • Synonymous with HPL terms for GPS • VPL is Vertical Protection Limit. Some NIC values also require a defined VPL.

  11. Current Specified 24 Satellite Constellation • Assumptions • 24 GPS Martinez constellation • Single-frequency receiver • Average availability of n-satellite failure (n=0-3) • Availability assessed over 24 hours with 5 minute intervals • No failures on operating satellites • GPS constellations considered parametrically (standard 24 SV and degraded: 23, 22, and 21 SV constellations) • No Baro Aiding or Inertial coasting capability in avionics • Mask Angle is the minimum angle above the horizon at which a GPS satellite would be used in the position calculation

  12. 24 Satellite Constellation – CONUS • Availability of HPL = 2NM (NIC = 4) • NIC 4 Supports 5NM En Route Separation 50 Mask Angle 24 of 24 23 of 24 Availability Scale 22 of 24 21 of 24

  13. 24 Satellite Constellation - CONUS • Availability of HPL = 0.6NM (NIC = 6) • NIC 6 Supports 5NM En Route; 3NM, 2.5NM and 1.5NM on Dependent Parallel Approach Terminal Separation Standards 50 Mask Angle 23 of 24 24 of 24 Availability Scale 22 of 24 21 of 24

  14. 24 Satellite Constellation - Alaska • Availability of HPL = 0.6NM (NIC = 6) • NIC 6 Supports 5NM En Route; 3NM, 2.5NM, and 1.5NM Terminal Separation Standards 50 Mask Angle 24 of 24 23 of 24 22 of 24 21 of 24 Availability Scale

  15. 24 Satellite Constellation • Availability of HPL = 0.2NM (NIC = 7) • NIC 7 Supports 5NM En Route; 3NM, 2.5NM, 1.5NM on Dependent Parallel, and 4300 feet on Independent Parallel Approach Terminal Separation Standards 20 Mask Angle 23 of 24 24 of 24 22 of 24 Availability Scale

  16. Future 24 Satellite Constellation • Assumptions • 24 GPS Martinez constellation • Dual frequency (L1, L5) constellation, dual frequency avionics • Average availability of n-satellite failure (n=0-3) • Availability assessed over 24 hours with 5 minute intervals • No failures on operating satellites • GPS constellations considered parametrically (24 SV and degraded: 23, 22, and 21 SV constellations) • No Baro Aiding or Inertial coasting capability in avionics

  17. Future 24 Satellite Constellation • Availability of HPL = 0.2NM (NIC = 7) • NIC 7 Supports 5NM En Route; 3NM, 2.5NM, 1.5NM on Dependent Parallel, and 4300 feet on Independent Parallel Approach Terminal Separation Standards 20 Mask Angle 23 of 24 24 of 24 Availability Scale 22 of 24

  18. 27/30 Satellite Constellations • Assumptions • Future GPS constellations - 27 satellite and 30 satellite constellations • Dual frequency (L1, L5) constellation, dual frequency avionics • Two and five degree mask angles • Average availability of n-satellite failures (n = 0, 1, 2) • No failures on operating satellites • Availability assessed over 24 hours with 5 minute intervals • No Baro Aiding or Inertial coasting capability in avionics

  19. 27 Satellite Constellation • Availability of HPL = 0.2NM (NIC = 7) • NIC 7 Supports 5NM En Route; 3NM, 2.5NM, 1.5NM Dependent Parallels and 4300 Feet Independent Parallel Terminal Separation Standards 50 Mask Angle 25 of 27 26 of 27 27 of 27 20 Mask Angle 25 of 27 26 of 27 27 of 27 Availability Scale

  20. 30 Satellite Constellation • Availability of HPL = 0.2NM (NIC = 7) • NIC 7 Supports 5NM En Route; 3NM, 2.5NM, 1.5NM Dependent Parallels and 4300 Feet Independent Parallel Terminal Separation Standards 50 Mask Angle 28 of 30 29 of 30 30 of 30 20 Mask Angle 28 of 30 29 of 30 30 of 30 Availability Scale

  21. Summary • GPS Constellations with greater numbers of satellites • Increase the availability for applying separation minima • Provide support for all current and potential future separation minima even with SV failures • Future Satellite Constellations with dual frequencies provide increased availability of separation minima

  22. Backup

  23. Conclusions • 24 Satellite Constellation with all satellites operational • Provides availability of >0.999 for 5NM En Route as well as 3NM, 2.5 NM and 1.5NM on Parallel Dependent Approach Terminal separation standards in most of CONUS and Alaska • Support for Independent parallel approach is unlikely with a 24 satellite constellation due to poor availability • Some areas in US have low availability (<0.999) of both terminal and En Route Separation Standards with a Mask Angle of either 2 or 5 degrees • Decreasing the Mask Angle accepted by the receiver increases availability but not sufficient to support separation standards in all of CONUS or Alaska • Any satellite failure results in poor availability (<0.99) for applying terminal or en route separations

  24. Conclusions • Future 24 Satellite Constellation • Provides availability of >0.99999 for 5NM En Route as well as all current Terminal separation standards with all satellites operational and a 2 degree mask angle • A single satellite failure results in maintaining an availability of 0.999 or greater in supporting all terminal and en route separtaion standards • When 2 or more satellites are failed GPS provides poor availability (<0.99) of integrity for applying en route and terminal separations

  25. Conclusions • 27 Satellite Constellation • Provides availability of >0.99999 to support all current separation standards • Provides availablity of a NIC that supports reduction of separation standards • Single satellite failure reduces availability of applying all separation standards in small area of CONUS to <0.999 when using a 5Mask Angle • Availability of all separation standards remains >0.99999 for a 2 Mask Angle during a single satellite failure. • Dual satellite failures degrades availability for applying today’s separation standards to as low as 0.99

  26. Conclusions • 30 Satellite Constellation • Provides availability of >0.99999 to support all current separation standards • Provides availablity of a NIC that supports reduction of separation standards • Single satellite failure does not impact availability of applying all current separation standards • Two satellite failures reduces availability of applying all separation standards • Over much of CONUS to >0.9999 when using a 5Mask Angle • In only small area of CONUS when using a 2 Mask Angle during a single satellite failure.

  27. 24 Satellite Constellation w/ WAAS - CONUS • Availability of HPL = 0.6NM (NIC = 6) • NIC 6 Supports 5NM En Route; 3NM, 2.5NM and 1.5NM on Parallel Independent Approach Terminal Separation Standards • 5 degree Mask Angle 23 of 24 24 of 24 22 of 24 21 of 24 Availability Scale

  28. 24 Satellite Constellation w/ WAAS - CONUS • Availability of HPL = 0.2NM (NIC = 7) • NIC 7 Supports 5NM En Route; 3NM, 2.5NM, 1.5NM Dependent Parallels and 4300 Feet Independent Parallel Terminal Separation Standards • 2 degree Mask Angle 24 of 24 23 of 24 22 of 24 Availability Scale

  29. 27/30 Satellite Constellation w/ WAAS • Availability of HPL = 0.2NM (NIC = 7) • NIC 7 Supports All En Route and Terminal Separation Standards 25 of 27 at 50 26 of 27 at 50 25 of 27 at 20 30 GPS Constellation 28 of 30 at 20 28 of 30 at 50 Availability Scale

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