Time Transfert by Laser Link
T2L2 On Jason 2
OCA –UMR Gemini Grasse – FRANCEEmail : [email protected]
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 : [email protected]
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
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
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