Post on 15-Jan-2016
NASA GPS ApplicationsNASA GPS Applications
Dr. Scott PaceAssociate Administrator for Program Analysis and EvaluationNASA
PNT Advisory Board
March 29, 2007
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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
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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
4Science 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
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Science Applications of GPS: Probing the Earth
IONOSPHEREIONOSPHEREOCEANSOCEANS SOLID EARTHSOLID EARTH
ATMOSPHEREATMOSPHERE
Significantwave heightSignificant
wave height
Ocean geoid andglobal circulationOcean geoid andglobal circulation
Surface windsand sea state
Surface windsand sea state
Short-term eddyscale circulationShort-term eddyscale circulation
OCEANSOCEANS
High resolution 3Dionospheric imagingHigh resolution 3D
ionospheric imaging
Ionospheric struc-ture & dynamics
Ionospheric struc-ture & dynamics
Iono/thermo/atmo-spheric interactionsIono/thermo/atmo-
spheric interactions
Onset, evolution& prediction ofSpace storms
Onset, evolution& prediction ofSpace storms
TIDs and globalenergy transportTIDs and globalenergy transport
Precise ion cal forOD, SAR, altimetryPrecise ion cal forOD, SAR, altimetry
IONOSPHEREIONOSPHERE
Climate change &weather modelingClimate change &weather modeling
Global profiles of atmosdensity, pressure, temp,and geopotential height
Global profiles of atmosdensity, pressure, temp,and geopotential height
Structure, evolutionof the tropopause
Structure, evolutionof the tropopause
Atmospheric winds,waves & turbulenceAtmospheric winds,waves & turbulence
Tropospheric watervapor distribution
Tropospheric watervapor distribution
Structure & evolutionof surface/atmosphere
boundary layer
Structure & evolutionof surface/atmosphere
boundary layer
ATMOSPHEREATMOSPHERE
Earth rotationPolar motion
Earth rotationPolar motion
Deformation of thecrust & lithosphereDeformation of thecrust & lithosphere
Location & motionof the geocenter
Location & motionof the geocenter
Gross massdistributionGross massdistribution
Structure, evolution of the deep interior
Structure, evolution of the deep interior
Shape of the earthShape of the earth
SOLID EARTHSOLID EARTH
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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
47o W171o W
85o E
~18-20o
7Search and Rescue with GPS:
Distress Alerting Satellite System
Uplink antenna
Downlink antenna
RepeaterSARSAT 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
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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
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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
10Navigation with GPS beyond Earth Orbit
… and on to the Moon
• GPS signals effective up to the Earth-Moon 1st 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
11Earth-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
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• 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
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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 timereference to another? …
Sun
Mars
Proper time as measured by clock on GPS satellite
GPS Satellite
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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) − 7.1Redshift (s per day) + 45.7Net secular effect (s per day) + 38.6Residual periodic effect * 46 ns (amplitude for e = 0.02)Sagnac effect * 133 ns (maximum for receiverat rest on geoid)
*Corrected in receiver
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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 SatellitesBeacons and/or GPS-like Satellites on
other Planetary Bodies
Ancient Sun Dial
Harrison Clock
GPS Satellites
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Backup Slides
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South Pole OutpostSouth 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.
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Concept Outpost Build Up
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KEY
Habitation
Solar Power Unit
Surface Mobility Carrier
Power Storage Unit
ISRU Module
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Logistics
Crew/Cargo Lander
Unpressurized Rover
Point of Departure Only – Not to Scale
Year 5-B Starts 6 month incrementsYear 5-B Starts 6 month incrementsYear 5
Year 5
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Notional Shackleton Crater Rim Outpost Location with Activity Zones
Notional Shackleton Crater Rim Outpost Location with Activity Zones
Habitation Zone
(ISS Modules Shown)
Power Production Zone
0 5 kmPotential Landing
Approach
50-60%60-70%>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
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Shackleton Crater Rim Size ComparisonShackleton 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!