Panel 1NPECAB

September 2007

Leadership Panel, Issue 1 Remove S/A Capability from System

• Background– Removal has been urged by independent

Panels for over 10 years– Capability is trivially defeated by GPS

differential Systems (WAAS, NDGPS, etc.)– It Flags the “Military Control of GPS”

The Good News: It was Officially removed by Secretary England at the urging of Dr. Schlesinger and announced

18 September 2007

Seattle RAIM Availability Comparison

2 Degree Mask AngleStandard 24 Satellite Constellation

SweetSpot

Prioritizing the “Big Five” Goals for GPS

1. Assured Availability of GPS signals-Including

impaired situations (mountains, urban areas, foliage,

etc.) (Signal has to be broadcast and in view)

2. Resistance to Interference (RFI) (User must

receive it)

3. Accuracy (Ranging Error and Geometry must meet need)

4. Bounded inaccuracy (Wild points limited by Good

Geometry and bounds on ranging error)

5. Integrity - eliminating HMI, meeting required

time to alarm (Satellite runaway must be very improbable)

THE “Big Five” Goals for GPS1. Assured Availability of GPS signals-Including impaired situations

(mountains, urban areas, foliage, etc.)– Number of GPS Satellites/Geometry– Interoperability and Standardization with Galileo et al

2. Resistance to Interference (RFI)– Additional Satellite RF power and Frequency Diversity– More jam resistant GPS receivers

3. Accuracy– Require Prediction Accuracy (Satellite Clocks and Age of Update)

– Good Satellite Geometry is essential– Augmentations: WAAS, LAAS,EGNOS, MSAS, NDGPS, PLs

4. Bounded inaccuracy to limit wild points– Concerned with the 1% or less “wild data points”– Good Satellite Geometry Coverage is Imperative

5. Integrity - eliminating HMI, meeting required time to alarm– RAIM– WAAS– Satellite Design – Self Checking

Three of top four Goals are driven by the number of satellites –

hence DSB & IRT 30+X satellite recommendation

A Caution: The Under - emphasized Goal

• For many users, accuracy is of less concern than the bounds on inaccuracy. – GPS errors do not follow a true Gaussian

(called Normal) distribution, particularly regarding outliers

– Need more emphasis on this element of the big 5.

• We should insure that all improvements are backward compatible.

More Observations

• Not practical for GPS to have service level based

guarantees that are universally useful to all users

• Perhaps a new paradigm of service is needed

– Define component services (e.g. pseudorange

accuracy) that will be exploited by all users to produce

required service levels

– Provide performance guarantees on components such

that end users can derive meaningful performance

measures in the context of their application

Panel 1: Meeting User Needs with Affordable Progress - Recommendations

1. Place GPS III quickly under contract with early

delivery

2. Formally Commit to current Level of Service

3. Insure Affordability – enable service without

brownouts

4. Place GPS signal and availability under a true

National Committee Tied to Approval Authority (strong participation by users as well as government agencies e.g. RTCA,

NSTAC)

The Brownout Danger

• Current GPS Average on-orbit life - 8.9 years• First IIF currently launch ready ICA 50%:

February 2009• First GPS III currently available for

Launch - December 2013

Needed: Sustained, high-level supportfor earlier GPS III delivery and availability

It is imperative the we avoid “GPS Brownouts”

Overview from GPS III IRT(one element)

• A 30+X constellation is much more important

& higher priority than Spot-Beams and Wide

Band Crosslinks

– Blindly pursuing all the current Requirements

would be expensive, risky & late

– Expensive, Complex Satellites will threaten

schedule and, ultimately, the constellation size

– Block size should be 8 to attain 30+X constellation

– Requires Senior acceptance and direction

Illustrating why current number of Satellites is Minimal (Courtesy GPS World and John Lavrakas)

• DOP is strongly driven by Masking Angle and number of satellites (the impaired user’s problem)

• Above 10o, less than 30 satellites destroys accuracy and availability

Monthly Availability of 24 sats 92 to

100%

DOP vs. Mask Angle (degrees) (June 6 2006)

The Knee

A New Development: Aircraft Landing and “Relative RAIM”

• Provides the integrity to allow aircraft to– Land at “regional” airports in bad weather– Use lightly instrumented third-world landing

fields with safety

• Without any Ground Augmentation• Potentially helps the military “Bounded

Inaccuracy” goal with a rigorous self check• Requires at least 30 satellites for reliable

operationRAIM – Receiver Autonomous Integrity Monitoring

- Use of more than minimum (4) satellites to determine the navigation signal is within normal error bounds

Integrity for ATC and Aircraft Landing using Relative RAIM

The Military Need for 30 + X

Summary

Background

• DSB Recommendations– To support all DOD users, & provide adequate

signal availability in urban canyons, mountainous terrain (typical masking angles of 15 to 20 degrees) the GPS constellation should be specified as 30 SVs plus adequate spares (30+X)

– To insure affordability, constrain GPS III satellite size to enable dual launch (insure 30 SVs are attainable)

– S/A capability-- no operational value: no further resources should be expended to place it

on GPS III

Reality Check – Mask Angle

• Extend right arm directly forward with thumb up

• Close the hand and form a fist

• The angle as seen from the bottom to the top of the fist is very close to 10 degrees

A 10 degree mask angle is totally unrepresentative

of mountains or urban areas

A 10 degree mask angle is totally unrepresentative

of mountains or urban areas

14th AF assessment of GPS operations in IRAQ & Afghanistan -- Feb 2006

• 14th AF Recent on-site Observations–Afghanistan

• Poor Availability--degraded due to mountains (high masking angles)

• Minimal RFI - terrain shielding

–Iraq• Jamming/RFI ~85% known blue force interference 15%

unknown• Number of GPS receivers Military & Civilian unknown -

significant number of both

•Availability Number one requirement

Availability Number one requirement

•Solution-More visible satellites

• Must solve the Jamming RFI Problem

• Solution- improved UE

[fixes already demonstrated]

Military Opns

in Impaired

Areas

Civil A/C Landing &

ADS-B Integrity

Clear Need for

“Specified”Constellation

of > 30 Satellites

TheNeed

Dual Launch?

(save>$50M/sat)

“Extra” Missions?

(900#Gorilla)

Cost per

Satellite

on Orbit

The Price

Must be Affordable

Budget Decisions

Battleship Galactica orAffordable First Step?

Meet orExceed Current

CapabilityOr Inevitable Brownouts?

Why Affordability is so Critical

Affordability Recommendation

• DOD should commit to providing a 30 Satellite constellation 98 % of the time and a 27 satellite constellation 100 % of the time

• To insure that commitment is met, steps should be taken to resist escalating costs:– Specify Dual Launch– Eliminate modules not essential to the primary

mission– Do not allow requirements creep to expand the IIIA

design beyond the essential first step

Panel 1 Summary: Meeting User Needs with Affordable Progress - Recommendations

1. Place GPS III quickly under contract with early delivery– Provides significant improvements over IIF– Insurance against Brownouts (150 million users)

2. Formally Commit to current Level of Service– So Civil Users can take advantage of proven capabilities– e.g. 30 + x Satellites Geometrically Optimized for Users– Insure Military Availability in impaired regions– Meet the Projected Capabilities of Compass and Galileo– Support world-wide use to reduce Aircraft congestion (RRAIM)

3. Insure Affordability – enable service without brownouts– Avoid non-GPS “requirements” (NDS et. al.) – Dual Launch– Fund a sensible fast-track development

4. Place GPS signal and availability under a true National Committee Tied to Approval Authority (strong participation by users as well as government agencies e.g. RTCA, NSTAC)– Assures signal is truly compatible and Maximizes Usefulness