NASA GPS Applications

1
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 / lt 5-cm orbit accuracy
• SAC-C 705-km alt / lt 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 Class
Turbo-Rogue (c. 92-99)
Jason Class
SAC-C Class
Grace Class
5
Science Applications of GPS Probing the Earth
SOLID EARTH
OCEANS
IONOSPHERE
ATMOSPHERE
6
Augmentation of GPS in Space GDGPS TASS

• TDRS Augmentation Service for Satellites (TASS)
  provides Global Differential GPS (GDGPS)
  corrections via TDRSS satellites
• Integrates NASAs Ground and Space
  Infrastructures
• Provides user navigational data needed to locate
  the orbit and position of NASA user satellites

7
Search and Rescue with GPSDistress Alerting
Satellite System

• 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

Repeater
Uplink antenna
Downlink antenna

• 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
GPS 35/36 Solid Coated Retroreflector

• 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

Hollow Cube and Array
The Gravity and Topography Fields need to be
referenced to WGS84 and ITRF
SLR CONOPS
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 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

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
Earth-Mars Communication and Navigation
Architecture

• 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

Current Mars Orbit Infrastructure
Evolutionary concept Add Satellite/s in
Areostationary orbit
13
Planetary Time Transfer
Proper time as measured by clock on Mars
spacecraft
Proper time as measured by clocks on Mars surface
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?
Mars Spacecraft
Mars
Mars to Earth Communications
GPS Satellite
Proper time as measured by clock on GPS satellite
Earth
Barycentric Coordinate Time (TCB)
Terrestrial Time (TT) International Atomic Time
(TAI) Coordinated Universal Time (UTC) GPS Time
Proper time as measured by clocks on Earths
surface
Sun
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) 45.7 Net secular effect (?s per day)
38.6 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
Ancient Sun Dial
Harrison Clock
GPS Satellites
Transit Satellites
Beacons and/or GPS-like Satellites on other
Planetary Bodies
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.

18
Concept Outpost Build Up
Year 5-B Starts 6 month increments
Point of Departure Only Not to Scale
19
Notional Shackleton Crater Rim Outpost Location
with Activity Zones
Potential Landing Approach
South Pole (Approx.)
Resource Zone (100 Football Fields Shown)
To Earth
Monthly Illumination (Southern Winter)
50-60
60-70
Landing Zone (40 Landings Shown)
Observation Zone
gt70
Power Production Zone
Habitation Zone (ISS Modules Shown)
Potential Landing Approach
5 km
0
20
Shackleton Crater Rim Size Comparison
Unique navigation challenges ahead!
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)