PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 0 Michael Pearlman Director Central Bureau International Laser Ranging Service Harvard-Smithsonian Center for Astrophysics Cambridge MA USA International Update on Satellite Laser Ranging (SLR)

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 1 GPS impact on Environmental Monitoring (examples) Cryospheric Science Sea Level Change Mass Transport Ocean Dynamics Atmospheric Dynamics 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)

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 2 Products of the Global Geodetic Observing System Terrestrial Reference Frame Accuracy of 1 mm and stability of 0.1 mm/yr. Products of the Global Geodetic Observing System Terrestrial Reference Frame Accuracy of 1 mm and stability of 0.1 mm/yr. Doppler Orbit Determination and Radiopositioning and Radiopositioning Integrated on Satellite Integrated on Satellite (IDS) (IDS) Very Long Baseline Interferometry(IVS) Satellite Laser Ranging (ILRS) (ILRS) Global Navigation Satellite Systems (IGS) (IGS), Precision GPS Orbits and Clocks, Earth Rotation Parameters, Station Positions International Earth Rotation Service (IERS),, International Terrestrial Reference Frame (ITRF)

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 3 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 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. Satellite Laser Ranging Technique

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 4 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

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 5 SLR Science and Applications Measurements F Precision Orbit Determination (POD) F Time History of Station Positions and Motions Products F Terrestrial Reference Frame (Center of Mass and Scale) F Plate Tectonics and Crustal Deformation F Static and Time-varying Gravity Field F Earth Orientation and Rotation (Polar Motion, length of day) F Orbits and Calibration of Altimetry Missions (Oceans, Ice) F Total Earth Mass Distribution F Space Science - Tether Dynamics, etc. F 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)

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 6 ILRS Network 33 global stations provide tracking data regularly Tracking about 25 satellites Most of the SLR stations co-located with GNSS

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 7 Selected SLR Stations Around the World Hartebeesthoek, South Africa TIGO, Concepcion, Chile MLRS, TX USA Matera, Italy Tahiti, French Polynesia Yarragadee, Australia Riyadh, Saudi Arabia Wettzell, Germany TROS, China Shanghai, China Kashima, Japan Zimmerwald, Switzerland NGSLR, Greenbelt, MD USA

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 8 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 2-KHz returns from Graz Station Pass Interleaving at Zimmerwald Station One-way ranging to LRO

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 9 NASA New Generation SLR System NASA’s Next Generation SLR (NGSLR), GGAO, Greenbelt, MD

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 10 Sample of SLR Satellite Constellation (HEO) Inclination64°55°55.5°56°0°0° Perigee ht. (km)19,14020,10021,50023,92036,000 Mass (kg)1, , GLONASSGPSGIOVEETS-8COMPASS

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 11 ILRS Retroreflector Standards for GNSS Satellites to 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 R**4 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).

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 12 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

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 13 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.

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 14 GOCE ESA LRO NASA ANDE NRL BLITS Russia GLONASS 115 Russia Missions for 2009 Jason-2 NASA/NOAA/CNES COMPASS (Beidou-2) China

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 15 Some people think the Earth looks like this: :

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 16 But really – it looks like this! :

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 17 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: F precise, continuous, robust, reliable, geographically well distributed F proper density over the continents and oceans F 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.

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 18 Value of SLR Tracking of the GNSS Constellations Geoscience F Improve the Terrestrial Reference Frame (space and ground co- location) F Distribute the reference frame globally; F Improve LEO POD for active satellites (altimeters, etc) GNSS World F Provide independent Quality Assurance: - The GNSS orbit accuracy cannot be directly validated from the GNSS data itself; F Assure interoperability amongst GPS, GLONASS, Galileo, COMPASS -; F Insure realization of WGS84 reference frame is consistent with ITRF; F Independent range for time transfer; F SLR is NOT required for use in routine/operational RF derived orbit and clock products

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 19 Terrestrial Reference Frame Two of the most demanding requirements for the TRF: F monitoring the water cycle at global to regional scales; F 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: F TRF should be accurate to 1 mm and stable to a 0.1 mm/yr, and F 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;

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 20 Benefit and Requirement SLR 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;

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 21 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 F Tracking of a subset of each constellation with a rotation through the entire constellation; simulations underway to help develop optimum strategies; F 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;

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | m 1 m 1 cm 1 mm.1 mm.01 mm.001 mm cm User Accuracy Requirement Trend Achieving the GGOS ITRF Requirements 1 mm accuracy 0.1 mm/yr stability Year 1 ns.1 ns 30 cm Current WGS 84 and GPS III Requirements Current Civilian and Scientific Requirements Position Accuracy Level Timing Accuracy Level We are here

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | m 1 m 1 cm 1 mm.1 mm.01 mm.001 mm cm User Accuracy Requirement Trend Achieving the GGOS ITRF Requirements 1 mm accuracy 0.1 mm/yr stability Year 1 ns.1 ns 30 cm Current WGS 84 and GPS III Requirements Current Civilian and Scientific Requirements Position Accuracy Level Timing Accuracy Level We need to be here

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | m 1 m 1 cm 1 mm.1 mm.01 mm.001 mm cm User Accuracy Requirement Trend Achieving the GGOS ITRF Requirements 1 mm accuracy 0.1 mm/yr stability Year 1 ns.1 ns 30 cm Current WGS 84 and GPS III Requirements Current Civilian and Scientific Requirements Position Accuracy Level Timing Accuracy Level We need to be here SLR tracking of GPS is required for this PNT improvement Co-location will deal with the systematic errors

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 25 We invite you to visit our