What is GEONS?

National Aeronautics and Space Administration

www.nasa.gov

NAVIGATION & MISSION DESIGN BRANCHNASA GSFC

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5What 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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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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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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Navigator Flight Unit 1A HWIL Testing for MMS Phase 2B

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Num

ber o

f GP

S

1210

86420

MMS Phase 2b, 1.2 x 25Re


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 < 1Clock Bias < 10 < 5 < 2 < 0.5

Pair of Relay Satellites at L2 provides one-way Doppler

Spacecraft receives GPS pseudorange enroute to Moon


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

More Details

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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


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


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


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)


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 0.201Comments 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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What is GEONS?

Documents

nasa gsfccelestial navigation

nasa gsfcrecognition

nasa gsfc1geons

geode software

seuve code

nasa software release

nasa gsfccislunar nav

nasa gsfcgeons core