1. NASA Update on GPS Use Dr. A.J. Oria
Overlook Systems Technologies, Inc. NASA H.Q. Ctr

2. Outline
International GPS Service (IGS) & Global Differential GPS (GDGPS)
TDRSS Augmentation Service for Satellites (TASS)
Distress Alerting Satellite System (DASS)

3. International GPS Service - Overview
What is IGS?
The International GPS Service (IGS) was formally recognized in 1993 by the International Association of Geodesy (IAG), and began routine operations on January 1, 1994
Over 10 years it has expanded to a coordinated network of over 300 GPS monitoring stations from 200 contributing organizations in 75 countries
Mission: “to provide a service to support, through GPS data products, geodetic and geophysical research activities” – IGS Terms of Reference
Collects, archives, processes, and distributes GPS observation data with typical 1 hour latency (not in real-time).
IGS Network Products:
High accuracy GPS orbits
Earth rotation parameters
IGS tracking station coordinates and velocities
GPS satellite and IGS tracking station clock information
Zenith tropospheric path delay estimates
Global ionospheric maps
Available at:
JPL
JPL
JPL
JPL
Goddard
JPL
JPL
(60 out of 286 NASA’s)
NASA Key Contribution Areas

4. NASA’s Contribution to IGS with GDGPS
Global Differential GPS (GDGPS)
Fully operational since 2000
60 dual-frequency GPS geodetic reference stations
10 cm horizontal & 20 cm vertical real-time positioning accuracy with dual frequency GPS receivers
10 cm level real–time orbit determination for LEO satellites with dual frequency GPS receivers may be possible
Not certified for safety-of-life applications
For more information:
Tracking Network of the International GPS Service
Highlighting NASA’s Contributions
NASA GPS Stations
NASA Cooperative Stations
Other Agency Stations

5. Probing the Earth with GPS
GDGPS as an Enabler -
Probing the Earth with GPS
Significant
wave height
Ocean geoid and
global circulation
Surface winds
and sea state
Short-term eddy
scale circulation
OCEANS
OCEANS
Earth rotation
Polar motion
Deformation of the
crust & lithosphere
Location & motion
of the geocenter
Gross mass
distribution
Structure, evolution
of the deep interior
Shape of the earth
SOLID EARTH
SOLID EARTH
High resolution 3D
ionospheric imaging
Ionospheric struc-
ture & dynamics
Iono/thermo/atmo-
spheric interactions
Onset, evolution
& prediction of
Space storms
TIDs and global
energy transport
Precise ion cal for
OD, SAR, altimetry
IONOSPHERE
Climate change &
weather modeling
Global profiles of atmos
density, pressure, temp,
and geopotential height
Structure, evolution
of the tropopause
Atmospheric winds,
waves & turbulence
Tropospheric water
vapor distribution
Structure & evolution
of surface/atmosphere
boundary layer
ATMOSPHERE
IONOSPHERE
ATMOSPHERE

6. GPS Technologies & Applications - Example – Geodesy & Oceanography
Gravity Field Measurements
GRACE dual-satellite mission
JPL GPS Receiver with integrated camera and K-band spacecraft to spacecraft tracking
1-micron accuracy measurement
Improve knowledge of the Earth’s gravity field by several orders of magnitude
Bi-Static Ocean Reflectrometry
Operational ocean altimeter calibrations for Navy and NASA

7. GDGPS - GPS Performance Monitoring The GDGPS GPS Integrity Monitor
The GDGPS System tracks each GPS satellite by at least 6 sites, and by 15 sites on average, enabling robust, real-time GPS performance monitoring with 4 sec to alarm
The GDGPS GPS Integrity Monitor

8. GDGPS - Integrity Monitoring
GDGPS is ideally suited for GPS integrity/performance monitoring:
State space approach (as in the OCS) enables separation of orbit and clock errors
Large global network allows estimation of clocks independent of models (unlike OCS), enabling prediction of integrity failures
Large global network enables implementation of majority voting schemes
High operational reliability
High performance monitoring: high accuracy, multiple metrics, absolute metrics
Independent of any other system employed in support of GPS operations
Leverage the NASA tens of million dollar investment in the GDGPS infrastructure
A prototype GPS integrity monitor was developed by JPL funded by IGEB and NASA
Operational since May 2003
100% availability to-date, with no known failures
No false alarms
All GPS anomalies monitored
Extremely positive feedback from 2SOPS

9. GDGPS & TASS (TDRSS Augmentation Service for Satellites)
GDGPS Operations Center
Frame
Internet
TASS (under development)
TDRSS
Uplink
NASA’s global real time network
Broadcast
Space users

10. Tracking and Data Relay Satellite System (TDRSS)
The Tracking and Data Relay Satellite Project (TDRS) system consists of in-orbit telecommunications satellites stationed at geosynchronous altitude and associated ground stations located at White Sands, New Mexico, and Guam.
Functions:
Space Network tracking.
Provide data, voice and video services to NASA scientific satellites, the Shuttle, International Space Station, and to other NASA missions.
Developing capability to provide user navigational data needed to locate the orbit and position of NASA user satellites.
F-5
174°W
TDW
F-7
171°W
Stored
F-1
049°W
F-6
047°W
TDS
F-4
041°W
TDE
F-3
275°W
TDZ
WHITE SANDS COMPLEX
GODDARD SPACE FLIGHT CENTER
GUAM REMOTE
GROUND TERMINAL
F-8
171.5°W
F-9
150°W
Test
F-10
150.7°W

11. TDRSS Augmentation Service for Satellites (TASS)
TASS provides NASAs GDGPS corrections via TDRSS satellites
Integrating NASA’s Ground and Space Infrastructures
Provides user navigational data needed to locate the orbit and position of NASA user satellites
47o W
171o W
85o E
~18-20o

12. Distress Alerting Satellite System (DASS)
Cospas-Sarsat System
International cooperative effort with Search & Rescue (SAR) payloads on numerous satellites and a worldwide network of 45 ground terminals
Relay distress signals from maritime, aviation, and land-based beacons
Over 17,000 lives saved to date
Known deficiencies including detection delay and location accuracy – based on 1970’s technology
DASS
1997 Canadian Follow-On SAR System (FOSS) study showed MEO constellation would provide an optimal follow-on space platform for greatly improved performance
SAR Payloads to fly on the GPS constellation
Under Development by the NASA SAR Mission Office in partnership with the DoD & Sandia National Labs (SNL) in support of the National SAR Committee (NSARC)
NASA, USAF SMC and ACC, DoE, NOAA, and USCG participate in MOA to conduct DASS POC
DASS Proof-of-Concept (POC)
406 MHz Uplink
S-Band downlink for POC
1544 MHz for OPS
SAR POC Ground Station(s)
SAR Aircraft
Beacons

13. Distress Alerting Satellite System (DASS)
DASS Provides
406 MHz ‘bent pipe’ repeaters on future GPS satellites
Full compatibility with existing and future 406 MHz beacons
Global near-instantaneous detection and location
Beacons without embedded GPS – greater than Cospas-Sarsat accuracy with 3 bursts or less
Self-locating beacons – GPS accuracy after single beacon burst
Support USAF/military SAR responsibilities
Alert data downlink freely available internationally
Low technical risk and low cost (uses modified existing GPS hardware)
Development Status
On-Orbit Testing
Two DASS satellites in-orbit, 3rd SVN60 / IIR-11 scheduled for early 2004
Testing performed (GSFC and SNL) using GPS IIR-07
Preliminary results support feasibility analysis
DASS POC Ground Equipment
Antenna system installation completed 3rd quarter 2004
Ground station equipment acquisition process by RFP in early 2004.
The DASS Local User Terminal being developed at GSFC
Ground Station Site Selection
Antennas on GSFC Building 28 roof, ground station equipment in Building 25
GSFC physical space construction detailed planning has begin
Optionally Could Provide
Short digital message return confirmation message
Aids in false alarm mitigation
Direct communications with survivors
Support rescue force coordination
Reduced interference susceptibility via confirmation

14. Contributors to this Presentation:
Dr. Lawrence Young – Jet Propulsion Lab
Allen Farrington – Earth Science Flight GPS Receiver Office, Jet Propulsion Laboratory
Dr. Yoaz Bar-Sever – Jet Propulsion Lab
Dr. Frank Bauer – Goddard Space Flight Center
Dave Affens - Goddard Space Flight Center
Dr. Michael Moreau – Goddard Space Flight Center
Roger J. Flaherty – Goddard Space Flight Center
Scott Murray – Johnson Space Center
Dr. Scott Pace – NASA Headquarters
Dr. A.J. Oria – Overlook Systems Technologies, Inc. / NASA HQ Ctr
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