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GPS–Enhanced Onboard Navigation System

Open architecture solutions for onboard orbit determination

NASA Goddard Space Flight Center invites companies to license its GEONS (GPS-Enhanced Onboard Navigation System) flight software package that provides onboard orbit determination and control in real time, with higher accuracy, without human intervention, and while requiring minimal onboard computing resources. It substantially improves definitive and predictive accuracy of Global Positioning System (GPS) receiver point solution fixes, achieving accuracies of at least 20 meters and 3 cm/sec.

GEONS was developed by researchers at Goddard to meet technology needs for:

  • Increased satellite autonomy
  • Support for collaborative science missions
  • GPS navigation to satellites with limited GPS visibility (e.g., high-Earth and geosynchronous missions)
  • Proposed formation flying/constellation missions
 Benefits 
  • Increases accuracy: GEONS reduces navigation errors by a factor of 15 in position and a factor of 50 in velocity when compared to traditional receiver solutions.
  • Improves reliability: GEONS can produce highly accurate orbit estimations even when only one GPS satellite is visible, greatly improving reliability for many applications.
  • Reduces mission cost: By enabling autonomous navigation, GEONS eliminates the need for ground-based orbit determination and tracking, while still allowing accurate ground-based monitoring and planning.
  • Enables satellite formation flying: Because it offers autonomous navigation, advanced mission concepts such as satellite formation flying are now possible.
  • Reduces computing requirements: GEONS requires minimal processing power, operating easily within limited onboard computer resources.
  • Improves stability: GEONS handles not only GPS data but also processes data used for other spacecraft functions. This fusion of data types increases stability and reliability and enables graceful degradation should a component fail.

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 Applications 

GEONS can be incorporated into science and technology applications including

  • HEO/LEO/GEO satellites
  • Spacecraft

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 Technology Details 

Standard GPS service computes real-time, three-dimensional spacecraft position and receiver time bias by using “point” or “geometric” solution methods. This method solves four simultaneous equations using four unknowns that are constructed using pseudo-range measurements from a minimum of four GPS satellites.

Because the geometric solutions are derived from measurements at a single point in time, they produce relatively poor velocity solutions and are not suitable for applications in which state vector information must be predicted ahead of time, e.g., to support autonomous maneuver planning. Geometric solutions can also undergo significant discontinuities when orbital motion introduces new GPS satellites into the calculated solution.

While real-time positioning is adequate for some onboard applications, position discontinuities are not acceptable for high-precision instrument applications, such as view-period prediction and maneuver planning, both of which are computations that require a continuous prediction of the spacecraft state. Real-time positioning also requires simultaneous measurements from four GPS satellites, a mission-limiting factor that must be considered.

Chart showing GEONS solution accuracy versus Point Solution accuracyHow it works

GEONS processes data from standard GPS receivers, onboard communication equipment, and/or attitude sensors, producing accurate absolute and relative navigation solutions in real time. Other functions, including onboard maneuver control and relative navigation for keeping formations are also supported by GEONS. Information is also quickly available to scientists when it is included in the down-linked telemetry stream.

GEONS provides high-quality solutions with fewer than four visible GPS space vehicles by employing an extended Kalman filter (EKF) augmented with physically representative models for gravity, atmospheric drag, solar radiation pressure, clock bias, and drift to provide accurate state estimation and a realistic state error covariance. GEONS incorporates the information from all past measurements—carefully balanced with GEONS' data of the physical models governing these measurements—to produce an optimal estimate of the user spacecraft's orbit. GEONS' high-fidelity state dynamics model reduces sensitivity to measurement errors and provides high-accuracy velocity estimates, permitting accurate state prediction during signal outages or degraded coverage.

Autonomous operation

Autonomous navigation reduces total mission cost by eliminating the need for routine, ground-based orbit determination and special tracking services. In addition to enabling the forwarding of information directly to the scientific investigators, onboard autonomous navigation products enable attitude control, maneuver planning, orbit control, and acquisition of communications signals. Autonomous navigation is required for advanced mission concepts, such as satellite formation flying.

GEONS was designed for autonomous operation within the very limited resources of an onboard computer. Autonomous initialization and enhanced fault detection capabilities are implemented using instantaneous geometric GPS solutions. GEONS' object-based design and open architecture make it highly reusable.

Why it is better

By incorporating information from past measurements, GEONS provides highly accurate orbit estimates even with only one visible GPS space vehicle—and even during signal outages or degraded coverage. This unprecedented accuracy and reliability reduces navigation errors by a factor of 15 in position and a factor of 50 in velocity compared to traditional receiver solutions—and does this autonomously with minimal onboard computer resources.

Additionally, GEONS not only incorporates algorithms that process pseudo-range and carrier phase data from GPS, it also processes 1-way Doppler measurements of the forward communications link, 1- and 2-way range and Doppler from intersatellite cross-links, and spacecraft-to-celestial-body-angle data from onboard attitude sensors. These different types of measurements are all incorporated into the GEONS software, providing a navigation system that is capable of handing multiple orbit regimes and navigation subsystems, while requiring no additional hardware. Fusion of these different data types enables graceful degradation in the event that a component fails during orbit and adds to the overall system stability and reliability.

Testing

Chart showing GEONS unprecedented autonomous position accuracyIn flight experiments using NASA LEO satellite data, GEONS-filtered GPS data produced position accuracies to better than 20 meters and velocity accuracies to better than 0.03 meters/second. Simulations indicate that the GEONS navigational software will achieve target performance goals of 10 meters and 0.01 meters per second for three-dimensional position and three-dimensional velocity accuracies respectively in LEO satellite mission applications. Goddard’s simulation results indicate navigation performance of better than 100 meters for position determination and 0.1 meter/second velocity determination for satellites operating in flight regimes well above the GPS constellation

GEONS Development History

GEONS combines the capabilities of several onboard orbit determination programs:

  • GEODE = GPS Enhanced Orbit Determination
    • Derived from TONS (TDRSS Onboard Navigation System) software
      • TONS currently providing operational OD onboard Terra
      • UD-Factorized sequential filter
      • Models based on GTDS (Goddard Trajectory Determination System) and RTOD (Real Time Orbit Determination)
    • Designed to operate in real time, hosted in Loral Tensor receiver
    • GEODE "Lite" integrated into EO-1 Autonomous formation flying experiment; provided real-time state feedback to formation controller
  • EONS = "Embedded Onboard Navigation System"
    • Another offshoot of TONS, supporting forward link 1-way Doppler navigation from GN contacts
    • Capability designed for nav processor board for General Dynamics Decision Systems’ 4th generation Ground Network (GN) transponder
  • Celnav = "Celestial Navigation"
    • Used measurements from attitude sensors to derive autonomous navigation solution
    • Based on standard techniques developed by Battin in 1960s for Apollo missions
  • GEONS = GEODE + EONS + Celnav
    • Simplified software maintenance with one set of source code
    • User can compile with only options needed

 (View development chart | PDF file)

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 Patents 

NASA Goddard Space Flight Center has copyrighted this software.

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 Publications 

(Links open new browser windows.)

The following articles have been written about GEONS and its predecessors (e.g., GEODE, EONS, etc.) (Links open new browser windows.)

  • "Relative Navigation Algorithms for Phase 1 of the MMS Formation" (D. Kelbel, et al.), Proceedings of the 2003 Flight Mechanics Symposium, NASA-CP-2003-212246
  • "GPS Navigation Results from the Low Power Transceiver" (L. Haas, et al.), Proceedings of the 2003 Flight Mechanics Symposium, NASA-CP-2003-212246.
  • "GPS-based Navigation and Orbit Determination for the AMSAT AO-40 Spacecraft" (G. Davis, et al.), Proceedings of the 2002 AIAA GNC Conference
  • "Preliminary Results of the GPS Flight Experiment on the High Earth Orbit AMSAT-OSCAR 40 Spacecraft" (M. Moreau, et al.), AAS Guidance and Control Meeting Paper No. AAS 02-004, Guidance and Control 2002
  • "Relative Navigation of Formation-Flying Satellites" (A. Long, et al.), Proceedings of the 2002 CNES International Symposium on Formation Flying Missions and Technologies
  • "Results from the GPS Flight Experiment on the High Earth Orbit AMSAT OSCAR-40 Spacecraft" (M. Moreau, et al.), Proceedings of the 2002 ION-GPS Meeting
  • "Evaluation of Relative Navigation Algorithms for Formation-Flying Satellites" (D. Kelbel, et al.), Proceedings of the 2001 Flight Mechanics Symposium, NASA/CP-2001-209986
  • "Autonomous Navigation Improvements for High-Earth Orbiters Using GPS" (A. Long, et al.), CNES 15th International Symposium on Space Flight Dynamics, June 26-30, 2000, Biarritz, France
  • "Autonomous Relative Navigation for Formation-Flying Satellites Using GPS" (C. Gramling, et al.), CNES 15th International Symposium on Space Flight Dynamics, June 26-30, 2000, Biarritz, France
  • "GPS Enhanced Orbit Determination (GEODE) Software" - Nomination document for NASA’s 2000 Software of the Year competition. (Awarded Runner-Up)
  • "GPS Receiver Architecture and Expected Performance for Autonomous GPS Navigation in Highly Eccentric Orbits," Proceedings of the 1999 Institute of Navigation Annual Meeting
  • "Autonomous Navigation of the SSTI/Lewis Spacecraft Using the Global Positioning System (GPS)," Proceedings of the 1997 GSFC Flight Mechanics and Estimation Theory Symposium
  • "GPS Navigation Initiatives at Goddard Space Flight Center Flight Dynamics Division," Proceedings of the 1997 American Astronautical Society Space Flight Mechanics Meeting
  • "Global Positioning System (GPS) Enhanced Orbit Determination Experiment (GEODE) on the Small Satellite Technology Initiative (SSTI) Lewis Spacecraft," Proceedings of the 1996 Institute of Navigation GPS Conference

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 Presentations 

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 Licensing and Partnering Opportunities 

This technology is part of NASA’s Innovative Partnerships Program Office, which seeks to transfer technology into and out of NASA to benefit the space program and U.S. industry. NASA invites companies to consider licensing the GEONS Software (GSC-14687-1) technology for commercial applications.

For information and forms related to the technology licensing and partnering process, please visit the Licensing and Partnering pages.

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 For More Information 

If you are interested in more information or want to pursue transfer of this technology (GSC-14687-1), please contact:

Innovative Partnerships Program Office
NASA Goddard Space Flight Center
Phone: (301) 286-5810
E-mail: geons@gsfc.nasa.gov

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