fundamental physics tests with cold atom clocks...

La Thuile, 20-27 March 2011 Gravitational Waves and Experimental Gravity 1

Fundamental Physics Tests with Cold Atom Clocks in Space

L. CacciapuotiEuropean Space Agency

The ACES Mission


ACES Mission Concept

ISS NASA CC

Columbus CC

HII-B launcher

HTV on-orbittransportation

TM/TC

MWL signal

Ground clocks

ISS

ACES payload

ACES USOC

ELT signal

SLR stations MWL GTs networkISS NASA CC

Columbus CC

HII-B launcher

HTV on-orbittransportation

TM/TC

MWL signal

Ground clocks

ISS

ACES payload

ACES USOC

ELT signal

SLR stations MWL GTs network


The Columbus Module


The ACES Payload– 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) Volume: 1172x867x1246 mm3

Mass: 227 kgPower: 450 W ASTRIUM

FCDP

GNSSReceiver

PHARAO

SHM

MWL

XPLC

PDU

S-bandKu-band

FCDP

GNSSReceiver

PHARAO

SHM

MWL

XPLC

PDU

S-bandKu-band


PHARAO: A Cold-Atom Clock in -gravity

Total volume: 990x336x444 mm3

Mass: 44 kg

PHARAO EM


PHARAO EM Accuracy Budget on Ground

Effect Frequency correction UncertaintyC field: 17nT C field: 35nT Cfield 1 Cfield 2

Blackbody 1.62510-14 2.2

10-16

Magnetic field -1.3016

10-13 -5.6328

10-13 6.6

10-16 14

10-16

Cold collision -5.3

10-15 9.5

10-16

Phase gradient -3.2

10-15

(due to ground operation)5

10-16

Total correction

-1.2715

10-13 -5. 6107

10-13 1.3

10-15 1.8

10-15

Expected PHARAO accuracy budget in microgravity at 1-3 10-16


PHARAO vs FOM Comparison

FPHARAO-FOM = 2.410-16

110-15


Flight Model of the PHARAO Tube


SHM: An Active H-maser for SpaceSHM role in ACES

– ACES flywheel oscillator– PHARAO characterization

Technical challenges– Low mass, volume, and power

consumption– Full performances:

• 1.510-13 @ 1 s• 1.510-15 @ 104 s

Design solution– Full size Al cavity– Automatic Cavity Tuning System

(ACT)Volume: 390x390x590 mm3

Mass: 42 kg


ACT Concept and Preliminary Tests

PID

Cavity varactor

Coh

eren

t det

ectio

n

AC

T in

ject

ion


SHM EM Assembly

Microwave cavity

H bulb Fourth magnetic

shield

Externalshield

cylinder


The ACES Clock Signal

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-loopLong-term servo-loop

– FLL correcting SHM clock signal against long-term drifts

– Frequency discriminator signal provided by Cs resonator and processed by XPLC

Stability of the ACES clock signal: - 310-15 at 300 s (ISS pass)- 310-16 at 1 day- 110-16 at 10 days

Accuracy: few parts10-16


PHARAO

ACES EM System Tests

LTSL

FCDP

SHM EM0

XPLC Crate

100 MHz

RF EGSE

Reference clocks

FOM CSOH-MSTSL


ACES Clock Signal Tested on Ground

1 10 100 1000 100001E-16

1E-15

1E-14

1E-13

1E-12 ACES on ground SHM EM0 PHARAO on ground FOM

Alla

n D

evia

tion

Time (s)


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 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

ASTRIUM


ACES MWL Performance Requirements

• 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

10-1 100 101 102 103 104 105 106 107

0,1

1

10

100 PHARAO SHM MWL

x(

) [p

s]

[s]


EM tests of the MWL FS Electronics

Carrier-phase stability

Code-phase stability

MWL FS electronics


• 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, power supply, and UPS housed in a separated support rack.

MWL Ground Terminal

Ground clocks synchronized to UTC to 0.5 s


UWA

TokyoPTBLNEUSNONIST

ISS

JPL

• Mission duration: 1.5 years up to 3 years• ISS orbit parameters:

– Altitude: ~ 400 km– 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

– Ground-to-ground down to the 10-17 after a few days of integration time• Common view• Non-common view

ACES Operational Scenario


ACES Mission Objectives ACES performances Scientific background and recent results

Fundamental physics tests

Measurement of the gravitational red

shift

Absolute measurement of the gravitational red- shift 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 at a precision level of

-1

d / dt < 110-17 year -1down to 310-18 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 , meee /QCD , and muuu /QCD .

Search for violations of

special relativity

Search for anisotropies of the speed of light at the level c / c < 10-10.

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.

ACES Mission Objectives


Relativistic Geodesy with ACES

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.

U1

U2


ELT Scientific Objectives• Clock Comparisons and Time Transfer

– Space-to-ground comparisons of clocks reaching a TDEV of 4 ps between 300 s and 104 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, two-

way optical ranging, microwave ranging – Analysis of atmosphere propagation delays


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

…and GNSS Applications


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


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 110-15.– Measurement of the Earth gravitational time dilation to a fractional

frequency uncertainty better than 210-7.– Measurement of the Sun gravitational time dilation to a fractional

frequency uncertainty better than 610-7.– Test of Lorentz Invariance in the matter and photon sector.


STE-QUEST Mission Concept• Baseline orbit: highly elliptic orbit:

– 700 km perigee, 51000 km apogee– U/c2~510-10

• On-board instruments– High-performance atomic clock: 310-14/ -1/2 instability, 110-16

inaccuracy– Time and frequency transfer link not degrading the clock

performance and able to compare ground clocks at the 110-18 level after a few days of integration time

– Dual atom interferometer: 110-15 g uncertainty to differential accelerations


STE-QUEST Mission Concept• Baseline orbit: highly elliptic orbit:

– 700 km perigee, 51000 km apogee– U/c2~510-10

• On-board instruments– High-performance atomic clock: 310-14/ -1/2 instability, 110-16

inaccuracy– Time and frequency transfer link not degrading the clock

performance and able to compare ground clocks at the 110-18 level after a few days of integration time

– Dual atom interferometer: 110-15 g uncertainty to differential accelerations

• Positively evaluated by the ESA Advisory Structure and accepted for an assessment study


… and thanks for your attention

fundamental physics tests with cold atom clocks...

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