# Presentation: 153684

## NASA Update on GPS Use

*Dr. A.J. Oria*
*Overlook Systems Technologies, Inc. NASA H.Q. Ctr*

## Outline

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

## International GPS Service - Overview

**NASA Key Contribution Areas**

**(60 out of 286 NASA’s)**

**JPL**

**JPL**

**JPL**

**JPL**

**JPL**

**JPL**

**Goddard**

**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:
- 	http://igscb.jpl.nasa.gov/components/prods.html

## NASA’s Contribution to IGS with GDGPS

**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: http://gipsy.jpl.nasa.gov/igdg

**NASA GPS Stations**
**NASA Cooperative Stations**
**Other Agency Stations**

**Tracking Network of the International GPS Service**
**Highlighting NASA’s Contributions**

## GDGPS as an Enabler -

**GDGPS as an Enabler -**
**Probing the Earth with GPS**

**IONOSPHERE**

**OCEANS**

**SOLID EARTH**

**ATMOSPHERE**

## GPS Technologies & Applications -Example – Geodesy & Oceanography

**Bi-Static Ocean Reflectrometry**
- Operational ocean altimeter calibrations for Navy and NASA

**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

## GDGPS - GPS Performance Monitoring

- 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**

## 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

## GDGPS & TASS (TDRSS Augmentation Service for Satellites)

***Uplink***

***Broadcast***

- TDRSS

- Space users

**TASS (under development)**

## 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.

## TDRSS Augmentation Service for Satellites (TASS)

**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**

## 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)**

## 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)

**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

**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

## Contributors to this Presentation:

- Dr. Lawrence Young – Jet Propulsion Lab
- 818-354-5018		_[Lawrence.E.Young@jpl.nasa.gov](mailto:Lawrence.E.Young@jpl.nasa.gov)_
- Allen Farrington – Earth Science Flight GPS Receiver Office, Jet Propulsion Laboratory
- 818-393-5260		Allen.H.Farrington@jpl.nasa.gov
- Dr. Yoaz Bar-Sever – Jet Propulsion Lab
- 818-354-2665		Yoaz.E.Bar-Sever@jpl.nasa.gov
- Dr. Frank Bauer – Goddard Space Flight Center
- 301-286-3102		Frank.Bauer@nasa.gov
- Dave Affens - Goddard Space Flight Center
- 301-286-9839		David.W.Affens@nasa.gov
- Dr. Michael Moreau – Goddard Space Flight Center
- 301-286-8382		Mike.Moreau@nasa.gov
- Roger J. Flaherty – Goddard Space Flight Center
- 301-286-7028		Roger.J.Flaherty@nasa.gov
- Scott Murray – Johnson Space Center
- 281-483-8242		Scott.V.Murray@nasa.gov
- Dr. Scott Pace – NASA Headquarters
- 202-358-1811		Scott.Pace@nasa.gov
- Dr. A.J. Oria – Overlook Systems Technologies, Inc. / NASA HQ Ctr
- 703-8931411 x 125	aoria@overlooksys.com

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