satellite system optis – a platform for precision experiments hansjörg dittus, c.lämmerzahl, s....

Satellite system OPTIS – A platform for precision experiments

Hansjörg Dittus, C.Lämmerzahl, S. Scheithauer ZARM, University of Bremen, Germany,

Achim Peters,

Humboldt University , Berlin, Germany

Stephan Schiller, Andreas Wicht Institute of Experimental Physics, Heinrich-Heine- University, Düsseldorf, Germany

OPTIS

ASTROD-Symp, Beijing, 14.7.2006

OPTISMotivation

Iso trop y o f c In d epen den ce o f c fromve lo c ity o f labo ra to ry

Tim e d ila tion

Special R elativity

Test of SR implies • Probing the structure of space-time• Test of Maxwell equations• Test of quantum gravity theories: Prediction of modified

Maxwell equations

W eak E qu iva len ceP rinc ip le

U n iversa lity ofG ravita tio na l R ed S h ift

S p ec ia l R e la tivity

G eneral R elativ ity G ravito m agn etice ffec ts

OPTISSTEP, MICROSCOPE

Test of GR implies• Test of quantum gravity theories• Tests of predicted violation of Weak Equivalence Principle• Tests of predicted violation of Universality of Gravitational Red Shift


OPTISScientific objectives

Isotropy of light propagation

Independence of velocity of light from velocity of laboratory

Universality of Gravitational Redshift

- comparison of clocks:

optical resonator – atomic clock – optical clock

Test of Lense-Thirring effect

Absolute gravitational redshift

Doppler effect

Perigee advance

Newtonian potential (Yukawa-like terms)

OPTIS: Improved Optical Tests for the Isotropy of Space

Improved experimental tests of:


OPTISExperimental goals

TestPresent Accuracy

OPTIS goal

Michelson- Morley1,5 · 10-9 10-12

Kennedy-Thorndike7 · 10-7 10-8

Time dilation / Doppler effect2 · 10-7 10-9

Universality Gravitational redshift 1cavity – clock comparison 1,7 · 10-2 10-4

Universality Gravitational redshift 2clock-clock comparison 2,5 · 10-5 10-7

Lense-Thirring effectvia laser tracking 3 · 10-1 10-8

Absolute gravitational redshifttime transfer 1,4 · 10--4 10-3

Perigee advancevia laser tracking 3 · 10--3 10-4

Newton potentialvia laser tracking 1 · 10-5 10-12


OPTIS

Mission Outline 1 (Baseline scenario)

to sunapogee 40000 km

perigee 10000 kmlaser

cavityfrequencycomparison

frequencycomparison

atomicclock(s)

frequencycomb

• Michelson-Morleylaser


• Univ. grav. red-shift

1( )U x

2( )U x

laser

cavity

frequencycomparison

atomicclock(s)

frequencycomb

• Kennedy-Thorndike

1

2



OPTISMission Outline 2

Lense-Thirring effect (orbit precession) Perigee shift Test of Yukawa part in Newtonian potential

High precision tracking by laser rangingin combination with drag free AOCS


OPTISMission main characteristics

Space conditions:

Long integration time Large velocity changes Large potential differences

Noise reduction:

Drag-free AOCS ( < 10-13 m/s2 @ 10-2 Hz)First time: combination of drag-free AOCS and laser rangingMonolithic resonatorSystematic elimination of distortions

New technologies in space:

Ultrastable lasersOptical frequency combResonators with narrow linewidthMicro-Propulsion systems (e.g. FEEPs, Colloidal thruster)Laser Link PlatformUltrastable atomic clocks


OPTISBasic principle to measure the isotropy of c

Usual 2nd-order approximation:

2

20

2

20

2

0 sinA1c

vB

c

vc,vc


OPTISMichelson-Morley (MM) experiment

Phase shift measurement

Brillet and Hall (1976)

Best measurement on Earth:

9105 B

laser


220

2

00

cos211

2Δ

c

vB

c

cc

f

ff


OPTISKennedey-Thorndike (KT) experiment

v

v

v

v

v0

vc

vA

f

f 202

Frequency change measurement:

Braxmaier, Müller, Pradl, Mlynek,Peters, and Schiller (2002)

Best measurement on Earth:

5101291 ..A

laser

cavity

frequencycomparison

atomicclock(s)

frequencycomb


OPTISTest of Universality of Gravitational Red Shift (2)

U1(r)

U2(r)

2

Δ

c

U

f

f

f

f

atomclockcavity

atomclock

atomclock

cavity

cavity

Frequency difference measurement:

Best measurements:

51012Δ .2102Δ

for H-maser Cs-clock

Cs-clockfor cavity

Bauch and Weyers (2002))

Turneaure and Stein (1987)

Signal signature of Red Shift violation differs from that of SRT violation due to velocity indepence !!!

laser

cavity

frequencycomparison

atomicclock(s)

frequencycomb


OPTISEffects measured by precise tracking

Lense-Thirring effect:Precession rates of knots

23

23223

232 1

6

1

2Ω

eac

)i(Jω,

eac

J

cosG

G

Perigee shift

223 122

eac

M

a

Mβγαω EE

GG

Test of the Newtonian potential

λ/rαr

MrU e

G1


OPTISMission Requirements

Variable spin rates(elimination of systematic errors) TSpin = 100 to 1,000 s

Cavity length variation requirement:δc/c < 10-18 σΔL (TSpin) / L < 10-18

Laser frequency lock instability: δc/c < 10-18 σlock(TSpin) / f < 10-18

Temperature stability for cavities: ΔTrandom < 200 µK,

ΔT (7 h) < 10 µK Independent clock reference for KT- experiment

reason for Gravitational Red shift experiment Comb generator must be used for comparison between atomic clock and cavity

δf/f < 10-15

Residual acceleration on board spacecraft δa < 10-13 m/s2 @ 10-2 Hz

Laser ranging δr < 1mm


OPTISKey technology: Optical cavity

single cavity: fused silica•Cavities: length ~ 5 cm (finesse ~ 100,000); effective length ~ 5000 m; better than interferometers: ~ 10 m

•Material: fused silica

• Length stability:ΔL = 10-16 m

• Temperature stability: ΔT < 10-8 K / √Hz but: for MM common mode rejection due to monolithic design: ΔT < 10-6 K / √Hz

•Residual accelerations

•Gravity gradient:10-13 m/(s2 · Hz)


OPTISResonator model

01

21

1

Urr

Elastic deformations under tidal forces

analytical solution by S. Scheithauer and C. Lämmerzahl

r Δr/R z Δz/L

R 6.2 · 10-15 L 1.6 · 10-13

R 6.5 · 10-14 0 0

Displacements for a 7000 km orbit


OPTISOPTIS resonator (FEM analysis)

calculated for a 7,000 km orbit


OPTISMirror displacements during orbit

relative displacement between 2 opposing mirrors

displacements at mirror midpoints


OPTISResonators and spin

Relative mirror displacements dx on x-axisOrbital rotation around y-axisSpin around z-axis


OPTISThermal gradients

Thermal gradient along z- axis: 10-9 K/L


OPTISKey technology: Lasers and electronicsLasers: langth, energy levels -> frequency

Diode-pumped Nd:YAG laser (1064 nm)

-Narrow linewidth

-High intensity stability

-High frequency stability

Ultrastable frequency lock on long time scales to cavities (Ruoso et al 1997, Braxmaier et al. 2002)

Also used for Earth-based GW interferometers

Lasers already space-qualified (Bosch)

Will be used for LISA-Pathfinder

RAV: 3·10-15 @ 100 s

10-5 of cavity linewidth


OPTISClocks

Frequency [GHz] Stability Operation in space

H-maser 1.420 405 751 10-15 GP-A, ACES, PHARAO, Galileo

Ion clock 40.507 347 996 5 . 10-16 GPS, SPACETIME

Cs atomic clock 9.192 613 770 10-13

Rb atomic clock 6.834 682 613 10-12 GPS, Galileo

Allan variance

Integration timeOPTIS requirement


OPTISKey technology: Frequency comb

( )t

Purpose: comparison of atomic clock frequency: 1010 Hz with optical frequency: 1015 Hz Accuracy: 10-15 Hz

1010 Hz1510 Hz

1510


OPTIS

Spacecraft and orbit (baseline scenario)

Mass 250 kgMass 250 kg

Power 250 WPower 250 W

High elliptic orbitPeriod: 14 hInclination 63°Shadow:

5 months without shadow 1 month with periodsSun rad. press. 4.4 μN/m2

Earth albedo rad. press. 1.2 μN/m2

Laser ranging platform

GTO

HEO

Apogee motorfor orbit transfer

FEEPs (???):ΔF = ± 0.1 μNFmax = 100 μN

+ Reference sensor δa=10-14 m/(s2·√ Hz)

In(Cs) Reservoir

ONERA

Cold gas thrusterfor coarse attitude control


OPTISOPTIS Summary

• Improved tests of isotropy and velocity-independence of c, universality of red shift, and gravitomagnetic tests

up to 1,000 times more accurate

Use of state-of-the-art technology

Ultrastable optical cavities Lasers Optical frequency comb Electronics and stabilization Micro-propulsion system Laser ranging High precision atomic clocks

• Optimal use of space conditions

Drag-free satellite control Long integration time High velocity Large gravitational potential changes

satellite system optis – a platform for precision experiments hansjörg dittus, c.lämmerzahl, s....

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