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:
GEONS can be incorporated into science and technology applications including
| 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.
How 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 measurementscarefully balanced with GEONS' data of the physical models governing these measurementsto 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 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 vehicleand 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 solutionsand 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.
In 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:
(View development chart | PDF file)
NASA Goddard Space Flight Center has copyrighted this software.
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The following articles have been written about GEONS and its predecessors (e.g., GEODE, EONS, etc.) (Links open new browser windows.)
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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 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