PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 0 Michael Pearlman Director...

PNT Advisory Board| Alexandria, Virginia | November 5 – 6 , 2009 | 1PNT Advisory Board| Alexandria, Virginia | November 5 – 6 , 2009 | 1

Michael PearlmanDirector

Central BureauInternational Laser Ranging Service

Harvard-Smithsonian Center for Astrophysics Cambridge MA USA

[email protected]

http://ilrs.gsfc.nasa.gov/index.html

International Update on Satellite Laser Ranging (SLR)


GPS impact on Environmental MonitoringGPS impact on Environmental Monitoring

(examples) (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)


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 DeterminationDoppler Orbit Determination and Radiopositioningand Radiopositioning Integrated on SatelliteIntegrated on Satellite

(IDS)(IDS)

Very Long BaselineVery Long BaselineInterferometryInterferometry

(IVS)(IVS)

Satellite LaserSatellite LaserRangingRanging (ILRS)(ILRS)

Global Navigation Global Navigation Satellite SystemsSatellite Systems

(IGS)(IGS)

,Precision GPS Orbits and Clocks, Earth Rotation Parameters, Station PositionsPrecision GPS Orbits and Clocks, Earth Rotation Parameters, Station Positions

International Earth Rotation ServiceInternational Earth Rotation Service(IERS)(IERS)

,,International Terrestrial Reference Frame (ITRF)


• 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


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


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)


ILRS Network

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


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, German

y

TROS, China

Shanghai, China

Kashima,Japan

Zimmerwald,

Switzerland

NGSLR, Greenbelt, MD

USA


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


NASA New Generation SLR System

NASA’s Next Generation SLR (NGSLR), GGAO, Greenbelt, MD


Sample of SLR Satellite Constellation(HEO)

Inclination 64° 55° 55.5° 56° 0°

Perigee ht. (km)

19,140 20,100 21,500 23,920 36,000

Mass (kg) 1,400 930 1,000 600 2800

GLO

NA

SS

GP

S

GIO

VE

ETS

-8

CO

MP

AS

S


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).


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


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.


GOCEESA

LRONASA

ANDENRL

BLITSRussia

GLONASS 115Russia

Missions for 2009

Jason-2NASA/NOAA/CNES

COMPASS (Beidou-2)

China


Some people think the Earth looks like this:

:


But really – it looks like this!

:


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.


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


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;


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;


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;


We invite you to visit our website @

http://ilrs.gsfc.nasa.gov/index.html

PNT Advisory Board| Alexandria, Virginia | November 5 – 6, 2009 | 0 Michael Pearlman Director...

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