Time Transfert by Laser Link

T2L2 On Jason 2

OCA –UMR Gemini Grasse – FRANCEEmail : etienne.samain@obs-azur.fr

E. Samain – Principal InvestigatorD. Albanese : OptiqueP. Exertier: Gemini DirectorM. Furia : ElectronicJ.F. Mangin : LaserJ. Paris : SoftwareF. Pierron: FTLRS J.M. Torre: Laser Station - ILRSP. Vrancken : Optical tests J. Weick : error - link Budget - computation

CNESToulouse – FranceEmail : phillipe.Guillemot@cnes.fr

P. Guillemot: System EngineerI. Petitbon: Project Manager

Principle

Retro-reflectors

Time Tagging of laser pulses emitted from a laser station in the satellite direction» Start Time at ground Station td (ground clock)

» Arrival time at satellite tb (space clock)

» Return Time at ground station tr (ground clock)

Time Transfer between Ground clock and Space clock» Triplet Construction for each laser pulse( td, tb,

tr)

» Computation of the time offset :

detector

clock

Atmospherelativitybrd ttt Re

2

Historical account

1972: Time transfer by laser link concept :LASSO (ESA, CNES)

1992: time transfer between McDonald and Grasse with LASSO

1996: T2L2 on MIR 99 (A Phase) 1997: T2L2 on ISS with ACES (B Phase) 2002: T2L2 on a Microsat Myriade CNES

2005 : T2L2 Accepted on board JASON 2

Jason 2

Ocean altimetry at the centimeter level Native Instruments

» Altimeter: Poseïdon 3 » Radiometer » Positioning systems: Doris – GPSP- Laser

ranging Passenger Instrument

» Radiation Measurements: LPT & Carmen 2» Time Transfer : T2L2

Orbit» Altitude 1336 km, i = 66°, P = 6800 s» Max distance in a common view mode : 6500

km» Time interval between pass 2h < T < 14h» 3 to 6 passes per day

T2L2 Payload T2L2 Instrument

» Event Timer» 2 optical channels: Linear – Geiger

Equipment available on Jason2» LRA : Laser Ranging Array» DORIS Ultra Stable Oscillator

T2L2 Space Instrument Synoptic

T2L2 Space Instrument

Jason 2Global View

T2L2 Field of view

From Space: +/- 55° for both T2L2 detection and LRA)

Ground StationPerformance Specifications

Event Timer:» Start Time» Return Time

Time stability requirement : below 1 ps over 1000s

Long term time stability: below 100 ps

Laser StationSpecifications

Wavelength 532 nm +/- 0.5 nm

Pulse Width: 20 to 200 ps @ FWHM

Minimum Energy per pulse : 10 mJ ; Nominal Energy: 50 mJ

Maximum  rate: above 1 kHz – Nominal rate: 10 Hz

Elevation range: 5° to 90°

No time synchronisation required

Ground stationEvent timer Status

Kit T2L2

OCA Equipment

Time Transfer» TwoWay» GPS mono and multi channels

Clocks» 2 Cesium 5071A» 1 Hydrogen maser

Laser Stations » FTLRS» MeO Station (LLR)

Scientific Objectives Time and Frequency metrology

Optical Laser Link validation »

» pour > 10000 s » Uncertainty < 100 ps

Ground clock Synchronization» Compatible with the best clocks available in world

Time scale participation» BIPM/CCD recommandation

2/113y 10 4.0 )(

s 0.1 10.17 10.28 0

2½152½122x

Scientific Objectives Time transfer Inter comparison

TWSTFT et GPS calibration» Common view: amelioration : 2 order of magnitude» Possibility to work on very wide bases: synchronization via

intermediate ground stations» Possibility to perform a direct GPS time transfer from the

GPS satellites to ground via T2L2: direct time tagging of the GPS PPS by the T2L2 space event timer-> GPS time transfer with out atmosphere perturbation

Validation & inter comparison of the ACES MWL

Scientific Objectives Fundamental Physics

Speed of light Anisotropy » Equivalent to the actual measurement: 2,7.10-9 (Oscillator

limitation)

Drift of the fine structure constant » Frequency comparison at the 5 10-17 level over 10 days » Measurement limited by the actual ground clocks

performances

Scientific Objectives One way laser ranging validation

Demonstrator of an interplanetary one way laser ranging based on clocks

One way Planetary (or moon) laser ranging

Scientific Objectives Observation & VLBI

Atmosphere» Light level measurement : far field Speckle

characterization

VLBI» integration time improvement» Antenna position

Jason-2 objectivesOrbitography

DORIS Oscillator characterization» Radiation and frequency drift correlation with CARMEN-2 &

LPT

Laser ranging improvement» One way laser ranging :Arrival time onboard Jason2 can be

used to reconstruct echoes » Direct evaluation of the LRA signature by comparison

between one way laser ranging and classical laser ranging

Development plan

B Phase: start 09/2005 ; end 01/2006 CD phases : start 01/2006 ; end 11/06 Jason2 integration : 01/2007

T2L2 working group constitution 2006 T2L2 Ground instrumentation 01/2007 Laser ranging station upgrade : 2008

Jason2 Launch : 06/2008 End of exploitation : 2013