GPS and Galileo Imagine the Possibilities

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GPS and Galileo Imagine the Possibilities

• R W Skinner
• Lockheed Martin Space Systems Company
• March 2, 2004

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• Within 6 years, the U.S. and Europe will operate
  a Second Generation Global Navigation Satellite
  System of 57 satellites.
• How good will the service be?

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Interoperability Framework

• Many definitions of interoperability framework
  exist
• LM recommends focus on system and services
  provided

Best for Users
Users use either or both systems at will
Convertible coordinate and time reference

• C2 systems pass
• Integrity data
• Anomaly data
• Scheduling data
• Measurements
• Messaging
• Command and Control ??

Increasing Level of Galileo/GPS Cooperation
Improved coverage and performance for dual system
users
Minimized interference and RF front end costs
Increasing Level of Benefit
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Big Constellation Advantage Availability of DOP
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GNSS Performance

• Worst-Case DOP All Satellites Operational

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GNSS Performance

• Worst-Case DOP, One GPS Satellite Out

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42/3 GNSS PDOP Performance
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54/6 GNSS PDOP Performance
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Big Constellation Advantage Receiver Based
Integrity
Scheduled Outage 0.0019
Unscheduled Outage 0.0019
Replacement Outage 0.0011
1. RAIM (27/3/1) 2. RAIM (30/6/GFE) 3. RAIM
(33/3/2) 4. RAIM (36/3/1)
5. RAIM (42/3/1) 6. Supplemental Integrity
Channel (27/3/1)
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Optimized GNSS

• U.S. and European Sub-Constellations in Similar
  Orbits
• Two 21 Satellite Sub-Constellations is Low Cost
• Worst-case PDOP lt 1.9
• RAIM availability of accuracy with integrity gt
  .999999
• Service availability tolerant at 2 satellites out
• Individual Sub-Constellation performance is Poor
• Two 27 Satellite Sub-Constellations Provides High
  Sub-Constellation Performance and Exquisite
• Worst-case PDOP lt 1.5
• RAIM availability of accuracy with integrity gt
  .9999999
• Sub-constellation unique services with high
  availability
• Immune to catastrophic, sub-constellation-wide
  failure

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Candidate Optimized Architecture

• 54 Satellite GNSS
• Two 27 satellite sub-constellations
• Complementary open access signal structure on all
  satellites
• Sub-constellation unique features
  (inter-satellite links, national security
  features, hosted payloads, regulated and
  commercial, etc.)
• 55º Inclination 23,616 km Altitude
• Alternating U.S. and European Satellites in 3
  Planes
• 18 satellites per plane, 20 in-plane spacing
• Plane 120º equatorial separation
• Independent, Coordinated Mission Control to
  Minimize Failures and Ensure Back-up
• Independent, All-in-View Monitoring Station
  Networks, with Shared Observations

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Conclusions

• GNSS of Complementary Sub-Constellations Improves
  Service
• Most Likely Combined Constellation Galileo
  GPS 27/6 Is The Lowest Performing Combined
  Constellation Analyzed
• Essential To Consider Constellation Orbitology
  and Operations Coordination For Best Service
  Delivery
• Further Harmonization and Rationalization of GPS
  and Galileo Have High Pay-off

Time Is Running Out Much More Technical and
Operational Work is Required