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The RTG (Real Time GIPSY) module of IGDG
combines uncompromisingly accurate satellite dynamic models
with a uniquely flexible filter
to provide unparelleled orbit determination capabilities
RTG provides the following:
- Optimized for real-time, autonomous radio metric data processing, orbit determination, and user positioning
- Compact - currently 30,000 lines of ANSI C code
- Designed to run in personal computers, small workstations, or flight computers (including processors embedded in GPS receivers)
- Design goals
- Retain the precision of the venerable GIPSY-OASIS software
- Minimize load size (400 kbytes) with fast throughput for flight cpus
- Widely portable
- Extensive error handling
- Dynamic memory allocation during run time to minimize memory use
- Precise dynamic models for orbiting receivers and transmitters
- Arbitrary size gravity fields
- State of the art Earth tide modesl (solid, ocean, polar)
- Drag model
- Solar pressure models
- Empirical spacecraft accelerations
- General purpose variable step integrator
- Precise observable models for receivers or transmitters on Earth
- General relativity and light time calculations
- General purpose factorized Kalman-type filter
- Current state or epoch state
- Process noise on any parameter
- Prediction residual test for outlier detection
RTG - Status
- Running continuously since November 1996 in real-time Wide Area Differential (WADGPS) processing
- Delivered to SATLOC in 1997 for commercial WADGPS operations
- Delivered to FAA in 1997 for operational WAAS implementation
- Delivered to Raytheon in 1997 for operational use in MSAS (a WAAS-like system in Japan)
- Used for orbit determination of the SNOE (Student Nitric Oxide Experiment) spacecraft
- Anticipated to be used operationally in at least four additional WAAS-like systems in South America
- Scheduled to fly on SAC-C GPS receiver, 2000.
- Scheduled to fly on ST-5 Communications and Navigation Transceiver (CCNT), 2003.
RTG - Portability and CPU Utilization
- RTG has been ported to the following platforms: VX Works, Linux, Unix, PowerPC, Windows NT
- Efficient CPU utilization
- RTG will use ~ 0.1% of 99 MHz HP 9000/735 workstation for low-Earth orbiter flight GPS data processing (at 0.03 Hz data rate)
- RAD6000 (RISC) flight processors are about 2.5 times slower
- Load size ~ 400 kbytes (currently)
RTG Model Status
| Model |
|
IERS |
|
GIPSY |
|
RTG |
| Geopotential |
|
GEM-T3 |
|
Any model (JGM3) any size |
|
Any model (JGM3) any size |
| Solid tide (dynamic) |
|
Wahr 2x2
6 constituents |
|
Wahr 3x3
47 constituents |
|
Wahr 3x3
47 constituents
|
| Solid tide (kinematic) |
|
 |
|
|
|
|
| Pole Tide |
|
|
|
|
|
|
| Ocean tide |
|
Schwiderski 6x2 |
|
CSR + TEG2B 20x10
767 constituents |
|
CSR + TEG2B
20x10 767
constituents |
| Ocean loading |
|
|
|
|
|
|
| Atmospheric loading |
|
|
|
|
|
|
| Troposphere |
|
Lanyi |
|
Lanyi/Neill |
|
Neill
|
| Solar pressure |
|
T20/Custom |
|
T20/Custom |
|
T20/Custom |
Relativity
(kinematic) |
|
|
|
|
|
|
Relativity
(dynamic) |
|
|
|
|
|
|
| Phase windup |
|
- |
|
|
|
|
| GPS Yaw |
|
- |
|
|
|
Being ported |
| Earth albedo & IR |
|
- |
|
|
|
Being ported |
| Atmospheric drag |
|
- |
|
|
|
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JPL's Real-Time Differential GPS Milestones
Operational Use of RTG by FAA
Example of Technology Transfer
- The FAA and its prime contractor (Raytheon, previously Hughes) have chosen JPL's RTG software for operational use
in the GPS Wide Area Augmentation System (WAAS). JPL started work Aug 12, 1996.
- Task plans, a NASA/FAA Interagency Agreement, and two software licenses are in place. WAAS has been run in test mode since 1999.
- WAAS will provide operational precise GPS-based navigation to airliners in U.S. airspace by 2001, and is slated to become sole navigation tool for US aviation by 2006.
- Another RTG software license was used by Rayhteon in implemented a WAAS-like system in Japan (MSAS). Implementation in several other countries is expected.
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