# Presentation: 486122

## 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**
**Required Integrity to Support Separation Standards**
**Current Specified 24 Satellite Constellation**
**Future 24 Satellite Constellation**
**27/30 Satellite Constellations**
**Conclusions**
**Next Steps**

## Separation Standards Analysis Objective

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

## 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

## 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**

## 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

## 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

**Notes:**
CAP risk is the risk that an aircraft with a displayed separation of 5NM, 3NM, or other separation minima, has a true separation of 200 feet or less.

## 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**

## MITRE CAP Model Analysis Results

| Operational Scenario | Minimum 
Separation 
(NM) | MSSR Radar
Range 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**

**Notes:**
Future Parallel Approach separation of 2500 feet is a lesser separation than existing PRM that is limited to runway spacing of 3400 feet or greater.

## NIC Relationship to Containment Radius (Rc)

**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)**

## 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

## 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

**5****0**** Mask Angle**

## 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

**5****0**** Mask Angle**

## 24 Satellite Constellation - Alaska

**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

**5****0**** Mask Angle**

## 24 Satellite Constellation

**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**

**2****0**** Mask Angle**

- 24 of 24

- 23 of 24

- 22 of 24

- Availability Scale

## 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

## Future 24 Satellite Constellation

**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**

**2****0**** Mask Angle**

- 24 of 24

- 23 of 24

- 22 of 24

- Availability Scale

## 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

## 27 Satellite Constellation

**27 Satellite Constellation**

- 27 of 27

- 26 of 27

- 25 of 27

**5****0**** Mask Angle**

- 27 of 27

- 26 of 27

- 25 of 27

**Availability Scale**

**2****0**** 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**

## 30 Satellite Constellation

**30 Satellite Constellation**

- 30 of 30

**5****0**** Mask Angle**

- 30 of 30

- 29 of 30

- 28 of 30

**Availability Scale**

**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**

- 29 of 30

- 28 of 30

**2****0**** Mask Angle**

## 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**

## Backup

## 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

## 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

## 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

## 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.

## 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

## 24 Satellite Constellation w/ WAAS - CONUS

**24 Satellite Constellation w/ WAAS - CONUS**

- 22 of 24

- Availability Scale

- 24 of 24

- 23 of 24

**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**

## 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**