ACES Atomic Clock Ensemble in Space Mission Status and Recent Test Results L.Cacciapuoti (ESA) Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 1
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 Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 2
The Columbus Module Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 3
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) Support subsystems (ESA) XPLC: External PL computer PDU: Power distribution unit, Mechanical, thermal subsystems CEPA: Columbus External PL Adapter (ESA-NASA) European Laser Timing (ELT) optical link (ESA) The ACES Payload XPLC GNSS antenna SHM PHARAO Volume: 1172x867x1246 mm 3 Mass: 227 kg Power: 450 W ASTRIUM Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 4 PDU FCDP PHARAO UGB MWL antennas GNSS Receiver MWL
PHARAO: A Cold-Atom Clock in µ-gravity PHARAO EM Total volume: 990x336x444 mm3 Mass: 44 kg Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 5
PHARAO EM Ramsey Interrogation S/N: ~10 1.0 3 Launch speed: 3.56 m/s Interaction time (T): ~100 ms ν 0.8 Ramsey =1/2T: ~5.6 Hz ν Rabi =2/(t 1 +t 2 ): ~170 Hz 0.6 0.4 0.2 Transition probability 0.0-300 -200-100 0 100 200 300 Frequency (Hz) Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 6
PHARAO EM Frequency Instability Internal mode: 3 10-13 @ 1s, limited by the USO and the short interrogation time achievable on ground. Measurements compatible with 7 10-14 τ 1/2 frequency instability in space. Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 7
SHM: An Active H-maser for Space SHM role in ACES ACES flywheel oscillator Coherent detection ACT injection Cavity varactor PID PHARAO characterization Technical challenges Low mass, volume, and power consumption Full performances: 1.5 10-13 @ 1 s 1.5 10-15 @ 10 4 s Design solution Full size Al cavity Volume: 390x390x590 mm 3 Mass: 42 kg Automatic Cavity Tuning System (ACT) Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 8
SHM EM Assembly Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 9
SHM Preliminary Measurements C-field: 600 µg Pulling Factor: 4.39 10-5 Hz/Hz Atomic Quality Factor: 1.0 10 9 Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 10
The ACES Clock Signal Stability of the ACES clock signal: - 3 10-15 at 300 s (ISS pass) - 3 10-16 at 1 day - 1 10-16 at 10 days Accuracy: ~1 10-16 Short-term servo-loop PLL stabilizing the PHARAO local 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 Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 11
FCDP EM some test results ASTRIUM Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 12
ACES Microwave Link Two-way link: Removal of the troposphere time delay (8.3-103 ns) Removal of 1st 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 (0.3-40 ns in S-band, 6-810 ps in Ku-band) Phase PN code modulation: Removal of 2π phase ambiguity High chip rate (100 MChip/s) on the code: Higher resolution Multipath suppression ASTRIUM Les Houches, 20 October 2009 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 GPhyS Kick-Off Colloquium 13
ACES MWL Performances 100 PHARAO SHM MWL 10 σ x (τ) [ps] 1 0,1 10-1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 τ [s] Time stability: 0.24 ps at 300 s, 5 ps at 1 day, 20 ps at 10 days of integration time Accuracy: absolute calibration at the 100 ps level Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 14
MWL EM performances Carrier-phase stability Code-phase stability Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 15
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 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 µs a (100 separated ps @ 10d support for at least rack. two ground clocks) Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 16
ACES EM System-level Tests Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 17
ACES Clocks Compatibility Tests PHARAO Allan Deviation with SHM ON in evaluation mode: servo-loop on the 9.192 GHz closed Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 18
ACES Clocks Compatibility Tests PHARAO Allan Deviation with SHM ON in autonomous mode: servo-loop on the 100 MHz closed Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 19
Next Steps Characterization of the short-term servo-loop ( ongoing) Characterization of the long-term servo-loop Long duration measurement: Long term stability Absolute frequency measurement with respect to the SYRTE mobile fountain clock FOM Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 20
ACES Operational Scenario Mission duration: 1.5 years up to 3 years ISS orbit parameters: Altitude: ~ 400 km NIST USNO LNE UWA Tokyo Inclination: ~ 51.6 Period: 90 min MWL ground terminals Located at ground clock sites Distributed worldwide: ~35 institutes interested in clock comparisons with ACES Clock comparisons via MWL and ELT Space-to-ground Link durations up to 400 seconds At least one useful ISS pass per day Ground-to-ground Common view Non-common view Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 21 PTB ISS
Ground Clock Comparisons via ACES MWL Space-based methods (~1000 km baseline): GPS (CP), TWSTFT, T2L2 on ground (~100 km baseline): Fibre-based links Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 22
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 < 50 10-6 after 300 s and < 2 10-6 after 10 days of integration time. Space-to-ground clock comparison at the 10-16 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 α at a precision level of α -1 dα / dt < 1 10-17 year -1 down to 3 10-18 year -1 in case of a mission duration of 3 years Optical clocks progress will allow clock-to-clock comparisons below the 10-17 level. Crossed comparisons of clocks based on different atomic elements will impose strong constraints on the time drifts of α, me /Λ QCD, and m u /Λ QCD. Search for violations of special relativity Search for anisotropies of the speed of light at the level δ c / c < 10-10. ACES results will improve present limits on the RMS parameter α based on fast ions spectroscopy and GPS satellites by one and two orders of magnitudes respectively. Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 23
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 10-17 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. Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 24
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 Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 25
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 Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 26
ACES Mission Milestones Closure of EM phase by end 2009 with the completion of ACES EM system level tests ACES PL CDR ACES Ground Segment PDR Start of FM phase in beginning 2010 Selection process of MWL Ground Terminal locations during 2010 MWL Ground Terminals deployment in 2012 Delivery of clocks FMs 2012 Ground segment operation readiness 2012 ACES ready for launch in 2013 Les Houches, 20 October 2009 GPhyS Kick-Off Colloquium 27