NASA GPS Applications Dr. Scott Pace Associate Administrator for Program Analysis and Evaluation NASA PNT Advisory Board March 29, 2007

2 GPS and Human Space Flight Miniaturized Airborne GPS Receiver (MAGR-S) Modified DoD receiver to replace TACAN on- board the Space Shuttle Designed to accept inertial aiding and capable of using PPS Single-string system (retaining three-string TACAN) installed on OV-103 Discovery and OV-104 Atlantis, three-string system installed on OV-105 Endeavour (TACAN removed) GPS taken to navigation for the first time on STS-115 / OV-104 Atlantis STS-115 Landing Space Integrated INS/GPS (SIGI) Receiver tested on shuttle flights prior to deployment on International Space Station (ISS) The ISS has an array of 4 antennas on the T1 truss assembly for orbit and attitude determination In operation

3 Navigation with GPS: Space-Based Range Space-based navigation, GPS, and Space Based Range Safety technologies are key components of the next generation launch and test range architecture Provides a more cost-effective launch and range safety infrastructure while augmenting range flexibility, safety, and operability Memorandum signed in November 2006 for GPS Metric Tracking (GPS MT) by January 1, 2011 for all DoD, NASA, and commercial vehicles launched at the Eastern and Western ranges GPS-TDRSS Space-Based Range

4 Science Applications of GPS: Blackjack Science Receivers Blackjack Family (’99 to present) Features: Developed at JPL and available in multiple configurations Tracks GPS occultations in both open-loop and closed-loop modes Tracks simultaneously from multiple antennas Missions: SRTM Feb 2000, CHAMP Jul 2000, SAC-C Nov 2000, JASON-1 Dec 2001, GRACEs 1 and 2 Mar 2002, FedSat Dec 2002, ICESat Jan 2003, COSMICs 1 through 6 Mar 2006, CnoFS Apr 2006, Terrasar-X Jul 2006, OSTM 2008 Results: Shuttle Radar Topography Mission (SRTM): 230- km alt / 45-cm orbit accuracy CHAMP: 470-km alt / < 5-cm orbit accuracy SAC-C: 705-km alt / < 5-cm orbit accuracy GRACE: 500-km alt (2 s/c) / 2-cm orbit accuracy, 10-psec relative timing, 1-micron K-band ranging, few arcsecond attitude accuracy with integrated star camera heads SRTM ClassTurbo-Rogue (c. ‘92-99) SAC-C Class Jason Class Grace Class

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

6 Augmentation of GPS in Space: GDGPS & TASS TDRS Augmentation Service for Satellites (TASS) provides Global Differential GPS (GDGPS) corrections via TDRSS satellites Integrates NASA’s Ground and Space Infrastructures Provides user navigational data needed to locate the orbit and position of NASA user satellites 47 o W 171 o W 85 o E ~18-20 o

7 Search and Rescue with GPS: Distress Alerting Satellite System Uplink antenna Downlink antenna Repeater SARSAT Mission Need: More than 800,000 emergency beacons in use worldwide by the civil community – most mandated by regulatory bodies Expect to have more than 100,000 emergency beacons in use by U.S. military services Since the first launch in 1982, current system has contributed to saving over 20,000 lives worldwide Status: SARSAT system to be discontinued as SAR payloads are implemented on Galileo 6 Proof-of-Concept DASS payloads on GPS $30M spent to-date by NASA

8 Maintaining and Enhancing GPS: Satellite Laser Ranging SLR Mission Need: Assuring of positioning quality, long term stability of GPS, by independent means Ensure independently from foreign sources consistency, or accuracy, between the definition of the WGS-84 reference frame and its practical realization Align the WGS-84 reference frame with the ITRF, the internationally accepted standard geodetic reference frame, to ensure GPS and Galileo long term interoperability ETOPO5- Orthometric EGM96- Orthometric The Gravity and Topography Fields need to be referenced to WGS84 and ITRF SLR CONOPS GPS 35/36 Solid Coated Retroreflector Hollow Cube and Array

9 Navigation with GPS beyond LEO GPS Terrestrial Service Volume –Up to 3000 km altitude –Many current applications GPS Space Service Volume (SSV) –3000 km altitude to GEO –Many emerging space users –Geostationary Satellites –High Earth Orbits (Apogee above GEO altitude) SSV users share unique GPS signal challenges –Signal availability becomes more limited –GPS first side lobe signals are important –Robust GPS signals in the Space Service Volume needed –NASA GPS Navigator Receiver in development

10 Navigation with GPS beyond Earth Orbit … and on to the Moon GPS signals effective up to the Earth-Moon 1 st Lagrange Point (L1) 322,000 km from Earth Approximately 4/5 the distance to the Moon GPS signals can be tracked to the surface of the Moon, but not usable with current GPS receiver technology

11 Earth-Moon Communications and Navigation Architecture Options for Communications and/or Navigation: –Earth-based tracking, GPS, Lunar-orbiting communication and navigation satellites with GPS-like signals, Lunar surface beacons and/or Pseudolites Objective: Integrated Interplanetary Communications, Time Dissemination, and Navigation

12 Architecture can accommodate evolutionary use of science orbiters as relays prior to deployment of any dedicated com/nav satellites at Mars Surface beacons possible in areas of interest Use of all available radiometric signals for positioning and navigation through integrated software defined radio (SDR) –SDR combines communications and navigation into a single device Evolutionary concept: Add Satellite/s in Areostationary orbit Current Mars Orbit Infrastructure Earth-Mars Communication and Navigation Architecture

13 Planetary Time Transfer Proper time as measured by clock on Mars spacecraft Mars to Earth Communications Proper time as measured by clocks on Mars surface Barycentric Coordinate Time (TCB  Proper time as measured by clocks on Earth’s surface Terrestrial Time (TT) International Atomic Time (TAI) Coordinated Universal Time (UTC) GPS Time Earth Mars Spacecraft Three relativistic effects contribute to different “times”: (1) Velocity (time dilation) (2) Gravitational Potential (red shift) (3) Sagnac Effect (rotating frame of reference) So how do we adjust from one time reference to another? … Sun Mars Proper time as measured by clock on GPS satellite GPS Satellite

14 GPS as a model for a Common Solar System Time GPS provides a model for timekeeping and time dissemination GPS timekeeping paradigm can be extended to support NASA space exploration objectives Common reference system with appropriate relativistic transformations Relativistic corrections in the GPS Time dilation (  s per day) − 7.1 Redshift (  s per day) Net secular effect (  s per day) Residual periodic effect * 46 ns (amplitude for e = 0.02) Sagnac effect * 133 ns (maximum for receiver at rest on geoid) *Corrected in receiver

15 The Future of Positioning, Navigation, and Timing? Pharos of Alexandria, Egypt Cape Henry, VA, Lighthouses (old and new) USCG Loran-C station, Pusan, South Korea, 1950s Transit Satellites Beacons and/or GPS-like Satellites on other Planetary Bodies Ancient Sun Dial Harrison Clock GPS Satellites

16 Backup Slides

17 South Pole Outpost Lunar South Pole selected as location for outpost site Elevated quantities of hydrogen, possibly water ice (e.g., Shackelton Crater) Several areas with greater than 80% sunlight and less extreme temperatures Incremental deployment of systems – one mission at a time –Power system –Communications/navigation –Habitat –Rovers –Etc. Lunar South Pole selected as location for outpost site Elevated quantities of hydrogen, possibly water ice (e.g., Shackelton Crater) Several areas with greater than 80% sunlight and less extreme temperatures Incremental deployment of systems – one mission at a time –Power system –Communications/navigation –Habitat –Rovers –Etc.

18 Concept Outpost Build Up KEY Habitation Solar Power Unit Surface Mobility Carrier Power Storage Unit ISRU Module Logistics Crew/Cargo Lander Unpressurized Rover Point of Departure Only – Not to Scale Year 5-B Starts 6 month increments Year 5

19 Notional Shackleton Crater Rim Outpost Location with Activity Zones Habitation Zone (ISS Modules Shown) Power Production Zone 0 5 km Potential Landing Approach % % >70 % Monthly Illumination (Southern Winter) Landing Zone (40 Landings Shown) Resource Zone (100 Football Fields Shown) Observation Zone To Earth South Pole (Approx.) Potential Landing Approach

20 Shackleton Crater Rim Size Comparison The area of Shackleton Crater rim illuminated approximately 80% of the lunar day in southern winter, with even better illumination in southern summer (Bussey et al., 1999) Note: ‘Red Zone’ = 750 m x 5 km (personal communication with Paul Spudis) Unique navigation challenges ahead!