Time Transfert by Laser Link T 2 L

Time Transfert by Laser Link T 2 L 2 On Jason 2 OCA –UMR Gemini CNES Grasse – FRANCE Email : etienne. samain@obs-azur. fr Toulouse – France Email : phillipe. Guillemot@cnes. fr E. Samain – Principal Investigator D. Albanese : Optique P. Exertier: Gemini Director M. Furia : Electronic J. F. Mangin : Laser J. Paris : Software F. Pierron: FTLRS J. M. Torre: Laser Station - ILRS P. Vrancken : Optical tests J. Weick : error - link Budget - computation P. Guillemot: System Engineer I. Petitbon: Project Manager

Principle l 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) l Time Transfer between Ground clock and Space clock » Triplet Construction for each laser pulse( td, tb, tr) » Computation of the time offset : Retroreflectors detector clock

Historical account l l 1972: Time transfer by laser link concept : LASSO (ESA, CNES) 1992: time transfer between Mc. Donald and Grasse with LASSO l 1996: T 2 L 2 on MIR 99 (A Phase) 1997: T 2 L 2 on ISS with ACES (B Phase) 2002: T 2 L 2 on a Microsat Myriade CNES l 2005 : T 2 L 2 Accepted on board JASON 2 l l

Jason 2 l l Ocean altimetry at the centimeter level Native Instruments » Altimeter: Poseïdon 3 » Radiometer » Positioning systems: Doris – GPSP- Laser ranging l Passenger Instrument » Radiation Measurements: LPT & Carmen 2 » Time Transfer : T 2 L 2 l Orbit » » Altitude 1336 km, i = 66°, P = 6800 s Max distance in a common view mode : 6500 km Time interval between pass 2 h < T < 14 h 3 to 6 passes per day

T 2 L 2 Payload l T 2 L 2 Instrument » Event Timer » 2 optical channels: Linear – Geiger l Equipment available on Jason 2 » LRA : Laser Ranging Array » DORIS Ultra Stable Oscillator

T 2 L 2 Space Instrument Synoptic

T 2 L 2 Space Instrument

Jason 2 Global View

T 2 L 2 Field of view l From Space: +/- 55° for both T 2 L 2 detection and LRA)

Ground Station Performance Specifications l Event Timer: » Start Time » Return Time l Time stability requirement : below 1 ps over 1000 s l Long term time stability: below 100 ps

Laser Station Specifications l Wavelength 532 nm +/- 0. 5 nm l Pulse Width: 20 to 200 ps @ FWHM l Minimum Energy per pulse : 10 m. J ; Nominal Energy: 50 m. J l Maximum rate: above 1 k. Hz – Nominal rate: 10 Hz l Elevation range: 5° to 90° l No time synchronisation required

Ground station Event timer Status Kit T 2 L 2

OCA Equipment l Time Transfer » Two. Way » GPS mono and multi channels l Clocks » 2 Cesium 5071 A » 1 Hydrogen maser l Laser Stations » FTLRS » Me. O Station (LLR)

Scientific Objectives Time and Frequency metrology l Optical Laser Link validation » » pour t > 10000 s » Uncertainty < 100 ps l Ground clock Synchronization » Compatible with the best clocks available in world l Time scale participation » BIPM/CCD recommandation

Scientific Objectives Time transfer Inter comparison l 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 T 2 L 2: direct time tagging of the GPS PPS by the T 2 L 2 space event timer-> GPS time transfer with out atmosphere perturbation l Validation & inter comparison of the ACES MWL

Scientific Objectives Fundamental Physics l Speed of light Anisotropy » Equivalent to the actual measurement: 2, 7. 10 -9 (Oscillator limitation) l Drift of the fine structure constant a » 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 l l Demonstrator of an interplanetary one way laser ranging based on clocks One way Planetary (or moon) laser ranging

Scientific Objectives Observation & VLBI l Atmosphere » Light level measurement : far field Speckle characterization l VLBI » integration time improvement » Antenna position

Jason-2 objectives Orbitography l DORIS Oscillator characterization » Radiation and frequency drift correlation with CARMEN-2 & LPT l Laser ranging improvement » One way laser ranging : Arrival time onboard Jason 2 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 l l l l B Phase: start 09/2005 ; end 01/2006 CD phases : start 01/2006 ; end 11/06 Jason 2 integration : 01/2007 T 2 L 2 working group constitution 2006 T 2 L 2 Ground instrumentation 01/2007 Laser ranging station upgrade : 2008 Jason 2 Launch : 06/2008 End of exploitation : 2013