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95What is GEONS?
Russell Carpenter
NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
GEONS Performs Onboard Navigation
Flight-proven Award-winning NPR 7150.2 Compliant UD-Factorized Extended
Kalman Filter ANSI standard C with
object-oriented techniques
GPS, TDRSS, DSN/USN/GN, Crosslink, Celestial Object, Accelerometer measurements
One or more user satellites, alone or simultaneously
Earth, Moon, LPOs, Deep Space
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NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
GEONS Core Algorithms and Software have 20+ years of Flight Heritage Ground-based experiments on Landsats 4 & 5, COBE (1980s)
led to series of experiments onboard EUVE (1990s) EUVE code formed basis for
- TDRSS Onboard Navigation System (TONS) now providing operational OD for Terra
- Enhanced Onboard Navigation System (EONS) that was integrated into the Command Receiver (forerunner to GD’s MMT)
- Celnav that was tested on the ground with POLAR and SOHO data TONS modified for GPS Enhanced Orbit Determination
Experiment (GEODE) on Lewis (1996)- GEODE “Lite” developed for EO-1 Autocon formation flying (2000)- GEODE software licensed to Orbital and Ball, has flown on numerous
missions including Microstars, Orbviews, SORCE, CALIPSO- GEODE embedded in ITT Low Power Transceiver and flown on STS-
107 CANDOS experiment GEONS = GEODE + EONS + Celnav (2001 - present)
- Simplified software maintenance with one set of source code; compile with only options needed
- Integrated with Navigator GPS for MMS and GPM
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NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Recognition and Compliance
Awards- 2000 Runner-up for NASA Software of the Year- 2004 Federal Laboratory Consortium Mid-Atlantic Regional
Excellence in Technology Transfer Award - 2007 NASA Software Release Award
NPR 7150.2 Compliance- Development of all core capabilities occurred prior to NPR 7150.2
(see previous slide) High-level requirements were documented in the “Software Requirements
Specifications” Detailed requirements were documented in the “Mathematical Specifications” “As-built” design was documented in the “System Description & User’s Guide”
- 7150.2 Compliant Software Maintenance Plan currently in effect Automated SCM, document repository, and issue tracking database in use by all
project personnel
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Performance
More Details
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NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Navigator Flight Unit 1A HWIL Testing for MMS Phase 2B
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Num
ber
of
GPS
1210
86420
MMS Phase 2b, 1.2 x 25Re
NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Cislunar Nav with GPS and Translunar Relay
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Position and Clock Errors [km] Near L1
Measure-ments
GPS Only 25 dB-Hz
GPS Only 18 dB-Hz
GPS Only 11 dB-Hz
GPS 25 dB-Hz, L2 Doppler
Radial < 10 < 5 < 2 < 0.5Cross-track < 1 < 0.5 < 0.1 < 1
Clock Bias < 10 < 5 < 2 < 0.5
Pair of Relay Satellites at L2 provides one-way Doppler
Spacecraft receives GPS pseudorange enroute to Moon
NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Celestial Navigation with ACS Sensor Data from HEO Spinner (POLAR)
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Horizon Sensor Measurement
Sun Sensor Measurement
1.8 x 9 Re Orbit, 10 RPM
Limited data: four 1-2 hour contacts over 4 days
“Truth orbit”- Ground-based 2-way
Doppler solution- Accuracy ~1 km
Attitude- Ground-based definitive- Accuracy ~6 arcmin
Simulated sensitivity to attitude bias:
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Algorithms
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NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Dynamics Models
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Primary coord sys
Mean equator and equinox of J2000.0 with analytic coordinate transformations
Primary time sys
Coordinated universal time (UTC)
Numerical integrator
Runge-Kutta 4th-and 8th order
Filter spacecraft orbit acceleration model
Joint Gravity Model-2 (JGM-2) geopotential up to degree 30 and order 30
LP100K non-spherical lunar potential model Other planetary non-spherical potential models Earth, solar, and lunar point masses with low precision analytic
ephemeris or Earth, solar, lunar, and planetary point masses with high precision analytic ephemeris or JPL Developmental Ephemeris
Analytic representation of Harris-Priester atmospheric density Solar radiation pressure with spherical or multi-plate area model for a
spinning spacecraft Measured accelerations in RIC, VBN, Spacecraft body, or Mean of
J2000.0 frames Impulsive delta-V maneuver model
Spacecraft orbit state transition matrix
Semi-analytic formulation including J2 and Earth and planetary point mass gravity, atmospheric drag, and solar radiation pressure acceleration partial derivatives
Second-order Gauss-Markov orbital covariance artificial damping
NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Estimator Models
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Estimator Extended Kalman filter with physically realistic process noise models and factored covariance matrix
Orbit estimation state
Position and velocity vectors for local and remote satellites, ground-based receiver or Moon-based receiver, or relative position and velocity vectors for remote satellites
Atmospheric drag coefficient correction for local and remote satellites or relative correction for remote satellites
Solar radiation pressure coefficient correction for local and remote satellites or relative correction for remote satellites
Clock bias, rate, and acceleration for local and remote satellites modeled as random walk, FOGM drift, or FOGM bias and SOGM drift processes, with relativistic correction
Unmodeled acceleration biases in the RIC, VBN, or spacecraft body frame
Pseudorange and Doppler biases for each GPS SV and WAAS GEO Integrated carrier phase biases for each GPS SV and GPS receiver Singly-differenced carrier phase biases for each GPS SV and remote
GPS receiver with respect to the local receiver Pseudorange and Doppler biases for each cross-link transmitter Ground-station-to-satellite range and Doppler biases for each Ground
Station Celestial object sensor biases Cross-link line-of-sight sensor biases TDRSS forward-link Doppler bias for each TDRSS satellite
NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Measurement Models and Cold Start
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Measurement model
Standard and singly differenced GPS pseudorange, Doppler, and integrated carrier phase with GPS receiver time and time bias corrections, single-frequency and dual-frequency ionospheric delay corrections, TASS Differential Corrections, and ICE Differential Correction parameters
Standard and singly differenced WAAS GEO pseudorange and Doppler with GPS receiver time and time bias corrections
Inter-satellite one-way and two-way cross-link pseudorange and Doppler with option to propagate transmitting satellite states if not being estimated
Point solution position and time bias Ground-station-to-satellite range and Doppler Line-of-sight vector to a celestial object (3-axis stabilized spacecraft) Cross-link line-of-sight vector to another satellite (3-axis stabilized
spacecraft) Sun sensor elevation angle (spinning spacecraft) Earth horizon crossing times (spinning spacecraft) Near-to-far-body pseudoangle Near-to-near-body pseudoangle TDRSS forward-link Doppler
Cold Start Initialization
Given nominal shape & orientation of orbit, solves for initial mean longitude using batch of pseudorange and Doppler
NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Other Models
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Maneuver targeting
Lambert iteration for Earth and planetary orbits
“Real-time” state propagation (between filter updates)
Earth point mass + J2
Attitude dynamics model
Gravity gradient and measured torques (math spec only as of Release 2.17)
Attitude estimation state
Attitude error, angular rate or gyro bias error, and antenna gain calibration coefficient states for each satellite (math spec only as of Release 2.17)
Attitude measurement model
GPS signal-to-noise ratio and double-difference carrier phase (math spec only as of Release 2.17)
NAVIGATION & MISSION DESIGN BRANCH, CODE 595NASA GSFC
Benchmarks for GEONS 2.1 (~2003)
GNU Profiler used to obtain average number of FLOPs per state update call over 10 samples in various configurations, compiled with full optimization
Four user satellites in 1.2 x 12 RE orbit with 24-hour period- Up to 12 GPS available below 3 RE; fewer than 4 GPS above 9 RE
All cases used 10-sec propagation time-step and 35 day time span
Four user states estimated, GPS only
Four users, GPS only
Four users, GPS + all 6 crosslinks
Single user, GPS + 3 local crosslinks
Seconds between updates
60 10 10 10
MFLOP per call 1.814 0.900 1.726 0.201
Comments Five prop-only cycles on each call
One prop cycle on each call
Crosslink processed 10 minutes each hour
Crosslink processed 10 minutes each hour
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