Michael Pearlman Director Central Bureau International Laser Ranging Service HarvardSmithsonian Cent

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Michael PearlmanDirectorCentral
BureauInternational Laser Ranging
ServiceHarvard-Smithsonian Center for
Astrophysics Cambridge MA USAmpearlman_at_cfa.harv
ard.edu
International Update on Satellite Laser Ranging
(SLR)
http//ilrs.gsfc.nasa.gov/index.html
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GPS impact on Environmental Monitoring (examples)

Mass Transport
Cryospheric Science

• GPS is essential to the measurement of
  environmental change.
• sea level change,
• ice budget,
• ocean circulation,
• land sequestration of water,
• atmospheric and
• space weather (GPS occultation)

Ocean Dynamics
Atmospheric Dynamics
Sea Level Change
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Products of the Global Geodetic Observing
System Terrestrial Reference Frame Accuracy of 1
mm and stability of 0.1 mm/yr.
,
International Terrestrial Reference Frame (ITRF)
International Earth Rotation Service (IERS)
,
Precision GPS Orbits and Clocks, Earth Rotation
Parameters, Station Positions
Doppler Orbit Determination and
Radiopositioning Integrated on Satellite (IDS)
Very Long Baseline Interferometry (IVS)
Satellite Laser Ranging (ILRS)
Global Navigation Satellite Systems (IGS)
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Satellite Laser Ranging Technique
Precise range measurement between an SLR ground
station and a retroreflector- equipped satellite
using ultrashort laser pulses corrected for
refraction, satellite center of mass, and the
internal delay of the ranging machine.

• Simple range measurement
• Space segment is passive
• Simple refraction model
• Night/Day Operation
• Near real-time global data availability
• Satellite altitudes from 300 km to synchronous
  satellites, and the Moon
• Cm satellite Orbit Accuracy
• Able to see small changes by looking at long time
  series

• Unambiguous centimeter accuracy orbits
• Long-term stable time series

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International Laser Ranging Service

• Established in 1998 as a service under the
  International Association of Geodesy (IAG)
• Collects, merges, analyzes, archives and
  distributes satellite and lunar laser ranging
  data for scientific, engineering, and operational
  needs
• Encourages the application of new technologies to
  enhance the quality, quantity, and cost
  effectiveness of its data products
• Produces standard products for the scientific and
  applications communities
• Includes 75 agencies in 26 countries.

ILRS Organization
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SLR Science and Applications

• Measurements
• Precision Orbit Determination (POD)
• Time History of Station Positions and Motions
• Products
• Terrestrial Reference Frame (Center of Mass and
  Scale)
• Plate Tectonics and Crustal Deformation
• Static and Time-varying Gravity Field
• Earth Orientation and Rotation (Polar Motion,
  length of day)
• Orbits and Calibration of Altimetry Missions
  (Oceans, Ice)
• Total Earth Mass Distribution
• Space Science - Tether Dynamics, etc.
• Relativity Measurements and Lunar Science
• More than 60 Space Missions Supported since 1970
• Four Missions Rescued in the Last Decade
• Most of the products that we generate (TRF. POD,
  EO, gravity field, etc) are done in conjunction
  with the other space techniques (GNSS, VLBI,
  DORIS)

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ILRS Network

• 33 global stations provide tracking data
  regularly
• Tracking about 25 satellites
• Most of the SLR stations co-located with GNSS

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Selected SLR Stations Around the World
Zimmerwald, Switzerland
Shanghai, China
NGSLR, Greenbelt, MD USA
Matera, Italy
MLRS, TX USA
Kashima, Japan
Riyadh, Saudi Arabia
TROS, China
Wettzell, Germany
Tahiti, French Polynesia
TIGO, Concepcion, Chile
Yarragadee, Australia
Hartebeesthoek, South Africa
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SLR Developments

• Higher repetition rate to increase data yield and
  improve pass-interleaving
• Eye-safe operations and auto tracking
• Automation (unattended operation)
• Event timers with near-ps resolution
• Web-based restricted tracking to protect
  optically vulnerable satellites (ICESat, ALOS,
  etc.)
• Two wavelength experiments to test refraction
  models
• Experiments continue to demonstrate optical
  transponders for interplanetary ranging LRO-LR
  one-way ranging to the Lunar Orbiter presently
  underway

One-way ranging to LRO
2-KHz returns from Graz Station
Pass Interleaving at Zimmerwald Station
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NASA New Generation SLR System
NASAs Next Generation SLR (NGSLR), GGAO,
Greenbelt, MD
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Sample of SLR Satellite Constellation(HEO)
GLONASS
COMPASS
GIOVE
ETS-8
GPS
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ILRS Retroreflector Standards for GNSS
Satellitesto increase tracking efficiency

• Retroreflector payloads for GNSS satellites in
  the neighborhood 20,000 km altitude should have a
  minimum  effective cross-section of 100 million
  sq. meters (5 times that of GPS-35 and -36)
• Retroreflector payloads for GNSS satellites in
  higher or lower orbits should have a minimum
  effective cross-section scaled to compensate
  for the R4 increase or decrease in signal
  strength
• The parameters necessary for the precise
  definition of the vectors between the effective
  reflection plane, the radiometric antenna phase
  center and the center of mass of the spacecraft
  should be specified and maintained with an
  accuracy better than 0.1 ppb (few mm).

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Current SLR Ranging to GNSS Satellites

• Operations include 7 GNSS satellites (GPS 36
  GLONASS 102, 109 and 115 GIOVE A and B and
  COMPASS M1)
• Satellite priorities set according to satellite
  altitude
• Track 5 minute segments at various points along
  the pass
• Data transmitted after each pass
• The data is available on the website within an
  hour or two
• Plenty of spare SLR tracking capacity
• Getting daylight ranging on new retroreflector
  arrays on GLONASS 115 and COMPASS M1

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ILRS Restricted Tracking

• ILRS authorization to track ILRS-approved
  satellites is constituted and governed by an
  approved Mission Support Request Form
• All SLR stations within the International Laser
  Ranging Service agree to adhere to any applicable
  ILRS Restricted Tracking Procedures including
• station by station authorization
• time and viewing angle constraints
• energy/power constraints
• go/no-go switch.

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Missions for 2009
GOCE ESA
ANDE NRL
Jason-2 NASA/NOAA/CNES
COMPASS (Beidou-2) China
LRO NASA
BLITS Russia
GLONASS 115 Russia
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Some people think the Earth looks like this

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But really it looks like this!

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Terrestrial Reference Frame (TRF)

• Provides the stable coordinate system that allows
  us to link measurements over space, time and
  evolving technologies
• An accurate, stable set of station positions and
  velocities
• Essential for tracking and interpreting flight
  missions
• Foundation for space-based and ground-based
  metric observations
• Established and maintained by the global space
  geodetic networks
• Network measurements must be
• precise, continuous, robust, reliable,
  geographically well distributed
• proper density over the continents and oceans
• interconnected by co-location of different
  observing techniques
• Strong Ground Network and a Strong Satellite
  Component with co-location at both ends
• Co-location at the analysis level.

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Value of SLR Tracking of the GNSS
Constellations

• Geoscience
• Improve the Terrestrial Reference Frame (space
  and ground co-location)
• Distribute the reference frame globally
• Improve LEO POD for active satellites
  (altimeters, etc)
• GNSS World
• Provide independent Quality Assurance - The GNSS
  orbit accuracy cannot be directly validated from
  the GNSS data itself
• Assure interoperability amongst GPS, GLONASS,
  Galileo, COMPASS -
• Insure realization of WGS84 reference frame is
  consistent with ITRF
• Independent range for time transfer
• SLR is NOT required for use in routine/operational
  RF derived orbit and clock products

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Terrestrial Reference Frame

• Two of the most demanding requirements for the
  TRF
• monitoring the water cycle at global to regional
  scales
• monitoring and modeling sea surface and ocean
  mass changes in order to detect global change
  signals in ocean currents, volume, mass and sea
  level
• Quantitatively
• TRF should be accurate to 1 mm and stable to a
  0.1 mm/yr, and
• Static geoid should be accurate to 1 mm and
  stable to a 0.1 mm/yr. (GGOS 2020, WCRP)
• A number of satellite missions are currently
  observing sea and ice topography with altimetry
  and mass transport in the water cycle through
  gravity missions
• Future altimetry and gravity field missions with
  improved capability are in the pipeline
• SAR and INSAR missions provide measurements of
  land surface displacements

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Benefit and RequirementSLR Tracking of GPS
Satellites

• What are the Benefits
• Improve in the accuracy and stability of the
  reference frame (Earth center of mass, scale,
  etc) by tracking of satellite constellation at
  higher altitudes
• Determine systematic errors among satellites in
  each constellation and among the constellations
  through co-location on the ground and in space
• Improve of global PNT, separate orbital errors
  from clock errors
• Use the GPS satellites to distribute the
  reference frame to everywhere on the Earth,
  provided we have accurate orbits for each GPS
  satellite
• What do need
• Retroreflector arrays on all of the GPS
  satellites
• Accurate center of mass correction on the
  satellites
• Accurate tracking of the satellites

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Concepts for an Operational GNSS Plan

• Support GPS, Galileo, GLONASS, and COMPASS
• Greater emphasis on more robust tracking and
  daylight ranging
• Increased tracking capacity with high repetition
  rate systems
• Newer retroreflector design
• Data available on the website shortly after each
  pass
• Possible tracking strategy
• Tracking of a subset of each constellation with a
  rotation through the entire constellation
  simulations underway to help develop optimum
  strategies
• For example
• one satellite per orbital plane per system at a
  time
• 60-day tracking cycles set to cover all
  satellites within a 12 month period
• Flexible tracking strategies organized in
  cooperation with the agencies involved and the
  requirements for the ITRF
• The network can be segmented to track different
  satellites
• ILRS analysts will do the data analysis and make
  the results available

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Achieving the GGOS ITRF Requirements 1 mm
accuracy 0.1 mm/yr stability
10 m
User Accuracy Requirement
1 m
1 ns
30 cm
Current WGS 84 and GPS III Requirements
10 cm
We are here
1 cm
Trend
Position Accuracy Level
Timing Accuracy Level
1 mm
.1 ns
.1 mm
Current Civilian and Scientific Requirements
.01 mm
.001 mm
Year
22
2010
2050
1970
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Achieving the GGOS ITRF Requirements 1 mm
accuracy 0.1 mm/yr stability
10 m
User Accuracy Requirement
1 m
1 ns
30 cm
Current WGS 84 and GPS III Requirements
10 cm
1 cm
Trend
Position Accuracy Level
Timing Accuracy Level
1 mm
.1 ns
.1 mm
Current Civilian and Scientific Requirements
.01 mm
We need to be here
.001 mm
Year
23
2010
2050
1970
25
Achieving the GGOS ITRF Requirements 1 mm
accuracy 0.1 mm/yr stability
10 m
User Accuracy Requirement
1 m
1 ns
30 cm
Current WGS 84 and GPS III Requirements
10 cm
1 cm
Trend
Position Accuracy Level
Timing Accuracy Level
1 mm
.1 ns
.1 mm
Current Civilian and Scientific Requirements
.01 mm
We need to be here

• SLR tracking of GPS is required for this PNT
  improvement
• Co-location will deal with the systematic errors

.001 mm
Year
24
2010
2050
1970
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We invite you to visit our website
_at_ http//ilrs.gsfc.nasa.gov/index.html