october 5, 2007 by: richard l. day, vice president en route and oceanic services (ato-e) federal...

October 5, 2007

By: Richard L. Day, Vice President En Route and Oceanic Services (ATO-E)

Federal AviationAdministration

Surveillance and Broadcast Services

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

Surveillance and Broadcast Services2Federal Aviation

Administration

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


Administration

Separation Standards Analysis Objective

• Determine the GPS constellation configuration that support various separation standards for the En Route and Terminal domains


Administration

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


Administration

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


Administration

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


Administration

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


Administration

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

Aw 0.033

0 20 40 60 80 100 120 140 1600

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

MSSR min separatnNIC/NACp separatnNUCp separatn

MSSR min separatnNIC/NACp separatnNUCp separatn

Range from MSSR, NM

App

aren

t sep

arat

ion

(NM

) for

CA

P=10

^-12

MSSR cross-range separation at CAP = 10^-12 as function of range compared with corresponding NIC/NACp (from 4/5 to 8/9) and NUCp (3 to 7) minimum separation at same CAP level


Administration

NIC/NACp Requirements for Close Approach Probability of 10-12 EquivalenceOperational Scenario Minimum

Separation (NM)

MSSR RadarRange in NM for CAP 10-12

Acceptable NIC/NAC for 10-12 CAP Risk

Supported ADS-B / ADS-B Separation (NM)

Supported Radar / ADS-B Separation (NM)

Supported Radar / Radar Separation (NM)

Radial or Orbit 5 135 4/5 3.2 4.2 5.0

Radial or Orbit 3 80 5/6 1.8 2.6 3.0

Approach 2.5 68 5/6 1.8 2.2 2.5

Parallel Dependent Approach

1.5 40 6/7 0.9 1.3 1.5

Parallel Independent Approach

0.71 (4300ft) 19 7/8 0.35 0.61 0.71

Future Parallel Independent Approach

0.41 (2500ft) 10 7/8 0.35 0.39 0.41

• 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

MITRE CAP Model Analysis Results


Administration

• 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.

NIC Relationship to Containment Radius (Rc)


Administration

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


Administration

24 Satellite Constellation – CONUS

Availability Scale

• Availability of HPL = 2NM (NIC = 4) • NIC 4 Supports 5NM En Route Separation

24 of 24 23 of 24

22 of 24 21 of 24

50 Mask Angle


Administration

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

24 of 24 23 of 24

22 of 24 21 of 24 Availability Scale

50 Mask Angle


Administration

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

24 of 24 23 of 24

22 of 24 21 of 24

Availability Scale

50 Mask Angle


Administration

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

24 of 24 23 of 24

22 of 24 Availability Scale


Administration

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


Administration

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

24 of 24 23 of 24



Administration

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


Administration

27 Satellite Constellation

27 of 27 26 of 27 25 of 27

50 Mask Angle

27 of 27 26 of 27 25 of 27Availability Scale

20 Mask Angle

• 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


Administration

30 Satellite Constellation

30 of 30

50 Mask Angle

30 of 30 29 of 30 28 of 30Availability Scale


4300 Feet Independent Parallel Terminal Separation Standards

29 of 30 28 of 30

20 Mask Angle


Administration

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

No SV Unusable

1 SV Unusable

2 SVs Unusable

No SV Unusable

1 SV Unusable

2 SVs Unusable

No SV Unusable

1 SV Unusable

2 SVs Unusable

No SV Unusable

1 SV Unusable

2 SVs Unusable

5NM En Route

Yes No No Yes Yes Possible Yes Yes Yes Yes Yes Yes3NM Terminal

Possible No No Yes Yes Possible Yes Yes Yes Yes Yes Yes2.5NM Terminal on Final Approach

Possible No No Yes Yes Possible Yes Yes Yes Yes Yes Yes1.5NM Terminal on Parallel Dependent Approach Possible No No Yes Yes Possible Yes Yes Yes Yes Yes Yes4300 Feet Terminal on Parallel Independent Approach No No No Yes Yes No Yes Yes No Yes Yes YesFuture Parallel Independent Approach at 2500 Feet No No No Yes Yes No Yes Yes No Yes Yes Yes

Separation Standard

Satellite Constellation Av >0.9999 (with 2 deg. Mask Angle)24 27 30Future 24


Administration

Backup


Administration

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


Administration

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


Administration

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


Administration

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.


Administration

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

24 of 24 23 of 24

22 of 24 21 of 24 Availability Scale


Administration

24 Satellite Constellation w/ WAAS - CONUS


24 of 24 23 of 24


4300 Feet Independent Parallel Terminal Separation Standards• 2 degree Mask Angle


Administration

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 20 26 of 27 at 50 25 of 27 at 50

30 GPS Constellation

28 of 30 at 20 28 of 30 at 50

Availability Scale

october 5, 2007 by: richard l. day, vice president en route and oceanic services (ato-e) federal...

Documents