The ACES Mission. Fundamental Physics Tests with Cold Atom Clocks in Space. L. Cacciapuoti European Space Agency

Transcription

1 The ACES Mission Fundamental Physics Tests with Cold Atom Clocks in Space L. Cacciapuoti European Space Agency La Thuile, March 2011 Gravitational Waves and Experimental Gravity 1

2 ACES Mission Concept ACES payload ISS HTV on-orbit transportation TM/TC ELT signal MWL signal HII-B launcher SLR stations MWL GTs network ISS NASA CC ACES USOC Columbus CC Ground clocks La Thuile, March 2011 Gravitational Waves and Experimental Gravity 2

3 The Columbus Module La Thuile, March 2011 Gravitational Waves and Experimental Gravity 3

4 PHARAO (CNES): Atomic clock based on laser cooled Cs atoms SHM (ESA): Active hydrogen maser FCDP (ESA): Clocks comparison and distribution MWL (ESA): T&F transfer link GNSS receiver (ESA) ELT (ESA): optical link Support subsystems (ESA) XPLC: External PL computer PDU: Power distribution unit, Mechanical, thermal subsystems CEPA: Columbus External PL Adapter (ESA-NASA) The ACES Payload XPLC FCDP PHARAO MWL GNSS Receiver Volume: 1172x867x1246 mm 3 Mass: 227 kg Power: 450 W ASTRIUM La Thuile, March 2011 Gravitational Waves and Experimental Gravity 4 PDU S-band SHM Ku-band

5 PHARAO: A Cold-Atom Clock in -gravity PHARAO EM Total volume: 990x336x444 mm 3 Mass: 44 kg La Thuile, March 2011 Gravitational Waves and Experimental Gravity 5

6 PHARAO EM Accuracy Budget on Ground Effect Frequency correction Uncertainty C field: 17nT C field: 35nT Cfield 1 Cfield 2 Blackbody Magnetic field Cold collision Phase gradient (due to ground operation) Total correction Expected PHARAO accuracy budget in microgravity at La Thuile, March 2011 Gravitational Waves and Experimental Gravity 6

7 PHARAO vs FOM Comparison F PHARAO-FOM = La Thuile, March 2011 Gravitational Waves and Experimental Gravity 7

8 Flight Model of the PHARAO Tube La Thuile, March 2011 Gravitational Waves and Experimental Gravity 8

9 SHM: An Active H-maser for Space Volume: 390x390x590 mm 3 Mass: 42 kg SHM role in ACES ACES flywheel oscillator PHARAO characterization Technical challenges Low mass, volume, and power consumption Full performances: s s Design solution Full size Al cavity Automatic Cavity Tuning System (ACT) La Thuile, March 2011 Gravitational Waves and Experimental Gravity 9

10 ACT Concept and Preliminary Tests Coherent detection ACT injection Cavity varactor PID La Thuile, March 2011 Gravitational Waves and Experimental Gravity 10

11 SHM EM Assembly H bulb Microwave cavity Fourth magnetic shield External shield cylinder La Thuile, March 2011 Gravitational Waves and Experimental Gravity 11

12 The ACES Clock Signal Stability of the ACES clock signal: at 300 s (ISS pass) at 1 day at 10 days Accuracy: few parts10-16 Short-term servo-loop PLL stabilizing the PHARAO loca l oscillator on the SHM clock signal FCDP processes the phase comparison signal and operates the servo-loop Long-term servo-loop FLL correcting SHM clock signal against long-term drifts Frequency discriminator signal provided by Cs resonator and processed by XPLC La Thuile, March 2011 Gravitational Waves and Experimental Gravity 12

13 ACES EM System Tests STSL FCDP FOM H-M CSO SHM EM0 Reference clocks PHARAO 100 MHz LTSL XPLC Crate RF EGSE La Thuile, March 2011 Gravitational Waves and Experimental Gravity 13

14 ACES Clock Signal Tested on Ground 1E-12 1E-13 ACES on ground SHM EM0 PHARAO on ground FOM Allan Deviation 1E-14 1E-15 1E Time (s) La Thuile, March 2011 Gravitational Waves and Experimental Gravity 14

15 ACES Microwave Link ASTRIUM Two-way link: Removal of the troposphere time delay ( ns) Removal of 1 st order Doppler effect Removal of instrumental delays and common mode effects Additional down-link in the S-band: Determination of the ionosphere TEC Correction of the ionosphere time delay ( ns in S-band, ps in Ku-band) Phase PN code modulation: Removal of 2 phase ambiguity High chip rate (100 MChip/s) on the code: Higher resolution Multipath suppression Carrier and code phase measurements (1 per second) Data link: 2 kbits/s on the S-band down-link to obtain clock comparison results in real time Up to 4 simultaneous space-to-ground clock comparisons La Thuile, March 2011 Gravitational Waves and Experimental Gravity 15

16 ACES MWL Performance Requirements 100 PHARAO SHM MWL 10 x ( ) [ps] 1 0, [s] Time stability: 0.24 ps at 300 s, 5 ps at 1 day, 20 ps at 10 days of integration time Accuracy: delays calibration for time transfer experiments at the 100 ps level La Thuile, March 2011 Gravitational Waves and Experimental Gravity 16

17 EM tests of the MWL FS Electronics Code-phase stability Carrier-phase stability MWL FS electronics La Thuile, March 2011 Gravitational Waves and Experimental Gravity 17

18 MWL Ground Terminal Electronics similar to MWL FS EU MWL GT EU attached to the steering unit to reduce phase instabilities due to tracking motion A computer controls the steering unit based on ISS orbit prediction files, collects telemetry and science data both from the local clock and the MWL GT electronics Directly interfaced to the ACES Users Support and Operation Center (USOC) for data exchange System protected by a radome cupola Thermal control, MWL GT computer, Ground power clocks supply, synchronized and UPS to housed UTC to 0.5 in s a separated support rack. La Thuile, March 2011 Gravitational Waves and Experimental Gravity 18

19 ACES Operational Scenario Mission duration: 1.5 years up to 3 years ISS orbit parameters: Altitude: ~ 400 km JPL NIST USNO LNE Inclination: ~ 51.6 Period: 90 min Clock comparisons Time and Frequency transfer links Microwave: MWL Optical: ELT Space-to-ground Link durations up to 400 seconds At least one useful ISS pass per day PTB Tokyo Ground-to-ground down to the after a few days of integration UWA time Common view Non-common view ISS La Thuile, March 2011 Gravitational Waves and Experimental Gravity 19

20 ACES Mission Objectives ACES Mission Objectives ACES performances Fundamental physics tests Scientific background and recent results Measurement of the gravitational red shift Absolute measurement of the gravitational redshift at an uncertainty level < after 300 s and < after 10 days of integration time. Space-to-ground clock comparison at the level, will yield a factor 35 improvement on previous measurements (GPA experiment). Search for time drifts of fundamental constants Time variations of the fine structure constant at a precision level of -1 d / dt < year -1 down to year -1 in case of a mission duration of 3 years Optical clocks progress will allow clock-to-clock comparisons below the level. Crossed comparisons of clocks based on different atomic elements will impose strong constraints on the time drifts of, me / QCD, and m u / QCD. Search for violations of special relativity Search for anisotropies of the speed of light at the level c / c < ACES results will improve present limits on the RMS parameter based on fast ions spectroscopy and GPS satellites by one and two orders of magnitudes respectively. La Thuile, March 2011 Gravitational Waves and Experimental Gravity 20

21 Relativistic Geodesy with ACES U 1 U 2 Relativistic geodesy: mapping of the Earth gravitational potential based on the precision measurement of the red-shift experienced by two clocks at two different locations ACES will perform intercontinental comparisons of optical clocks at the level after 1 week of integration time, measuring the local height of the geoid at the 10 cm level. The global coverage offered by ACES will complement the results of the CHAMP, GRACE, and GOCE missions. La Thuile, March 2011 Gravitational Waves and Experimental Gravity 21

22 ELT Scientific Objectives Clock Comparisons and Time Transfer Space-to-ground comparisons of clocks reaching a TDEV of 4 ps between 300 s and 10 4 s of integration time, better than 7 ps on the long-term CV comparisons below 6 ps per ISS pass Non-CV comparisons below 6 ps after 2000 s of dead time Space-to-ground and ground-to-ground synchronization of clocks Laser Ranging Laser ranging performance at the centimetre level per single shot (50 ps one-way) Comparison of ranging techniques: one-way optical ranging, twoway optical ranging, microwave ranging Analysis of atmosphere propagation delays La Thuile, March 2011 Gravitational Waves and Experimental Gravity 22

23 and GNSS Applications ACES and the GNSS network Orbit determination as operational function and support applications in the areas of: GNSS time and frequency transfer Radio-occultation experiments Coherent reflectometry experiments La Thuile, March 2011 Gravitational Waves and Experimental Gravity 23

24 ACES Mission Milestones ACES EM phase closed Upcoming test activities SHM EM1 end-to-end tests MWL end-to-end tests FM phase started Selection process of MWL Ground Terminal locations by 2011 MWL Ground Terminals deployment in end 2012 ACES ready for launch in 2014 La Thuile, March 2011 Gravitational Waves and Experimental Gravity 24

25 STE-QUEST Proposed by the scientific community at the last Call for Medium Size Mission Opportunity in the frame of the ESA Cosmic Vision Plan. STE-QUEST science goal: Test the different aspect of the Einstein Equivalence Principle Test of the universality of free fall on quantum objects to an uncertainty in the Eötvös parameter better than Measurement of the Earth gravitational time dilation to a fractional frequency uncertainty better than Measurement of the Sun gravitational time dilation to a fractional frequency uncertainty better than Test of Lorentz Invariance in the matter and photon sector. La Thuile, March 2011 Gravitational Waves and Experimental Gravity 25

26 STE-QUEST Mission Concept Baseline orbit: highly elliptic orbit: 700 km perigee, km apogee U/c 2 ~ On-board instruments High-performance atomic clock: / -1/2 instability, inaccuracy Time and frequency transfer link not degrading the clock performance and able to compare ground clocks at the level after a few days of integration time Dual atom interferometer: g uncertainty to differential accelerations La Thuile, March 2011 Gravitational Waves and Experimental Gravity 26

27 STE-QUEST Mission Concept Baseline orbit: highly elliptic orbit: 700 km perigee, km apogee U/c 2 ~ On-board instruments High-performance atomic clock: / -1/2 instability, inaccuracy Time and frequency transfer link not degrading the clock performance and able to compare ground clocks at the level after a few days of integration time Dual atom interferometer: g uncertainty to differential accelerations Positively evaluated by the ESA Advisory Structure and accepted for an assessment study La Thuile, March 2011 Gravitational Waves and Experimental Gravity 27

28 and thanks for your attention La Thuile, March 2011 Gravitational Waves and Experimental Gravity 28