1. Time Transfert by Laser Link T2L2 On Jason 2 OCA –UMR Gemini Grasse – FRANCE Email : etienne.samain@obs-azur.fretienne.samain@obs-azur.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 CNES Toulouse – France Email : phillipe.Guillemot@cnes.frphillipe.Guillemot@cnes.fr P. Guillemot: System Engineer I. Petitbon: Project Manager

2. Principle Retro- reflectors l Time Tagging of laser pulses emitted from a laser station in the satellite direction »Start Time at ground Station t d (ground clock) »Arrival time at satellite t b (space clock) »Return Time at ground station t r (ground clock) l Time Transfer between Ground clock and Space clock »Triplet Construction for each laser pulse( t d, t b, t r ) »Computation of the time offset : detector clock

3. Historical account l 1972: Time transfer by laser link concept :LASSO (ESA, CNES) 1992: time transfer between McDonald and Grasse with LASSO l 1996: T2L2 on MIR 99 (A Phase) l 1997: T2L2 on ISS with ACES (B Phase) l 2002: T2L2 on a Microsat Myriade CNES l 2005 : T2L2 Accepted on board JASON 2

4. Jason 2 l Ocean altimetry at the centimeter level l Native Instruments »Altimeter: Poseïdon 3 »Radiometer »Positioning systems: Doris – GPSP- Laser ranging l Passenger Instrument »Radiation Measurements: LPT & Carmen 2 »Time Transfer : T2L2 l 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

5. T2L2 Payload l T2L2 Instrument »Event Timer »2 optical channels: Linear – Geiger l Equipment available on Jason2 »LRA : Laser Ranging Array »DORIS Ultra Stable Oscillator

6. T2L2 Space Instrument Synoptic

7. T2L2 Space Instrument

8. Jason 2 Global View

9. T2L2 Field of view l From Space: +/- 55° for both T2L2 detection and LRA)

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

11. Laser Station Specifications l Wavelength 532 nm +/- 0.5 nm l Pulse Width: 20 to 200 ps @ FWHM l Minimum Energy per pulse : 10 mJ ; Nominal Energy: 50 mJ l Maximum rate: above 1 kHz – Nominal rate: 10 Hz l Elevation range: 5° to 90° l No time synchronisation required

12. Ground station Event timer Status Kit T2L2

13. OCA Equipment l Time Transfer »TwoWay »GPS mono and multi channels l Clocks »2 Cesium 5071A »1 Hydrogen maser l Laser Stations »FTLRS »MeO Station (LLR)

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

15. 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 T2L2: direct time tagging of the GPS PPS by the T2L2 space event timer-> GPS time transfer with out atmosphere perturbation l Validation & inter comparison of the ACES MWL

16. Scientific Objectives Fundamental Physics l 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

17. Scientific Objectives One way laser ranging validation l Demonstrator of an interplanetary one way laser ranging based on clocks l One way Planetary (or moon) laser ranging

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

19. 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 Jason2 can be used to reconstruct echoes »Direct evaluation of the LRA signature by comparison between one way laser ranging and classical laser ranging

20. Development plan l B Phase: start 09/2005 ; end 01/2006 l CD phases : start 01/2006 ; end 11/06 l Jason2 integration : 01/2007 l T2L2 working group constitution 2006 l T2L2 Ground instrumentation 01/2007 l Laser ranging station upgrade : 2008 l Jason2 Launch : 06/2008 l End of exploitation : 2013