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, OPTIS Motivation Test of SR implies Probing the structure of space-time Test of Maxwell equations Test of quantum gravity theories: Prediction of modified Maxwell equations OPTIS STEP, 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

ASTROD-Symp, Beijing, OPTIS Scientific 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:

ASTROD-Symp, Beijing, OPTIS Experimental goals Test Present Accuracy OPTIS goal Michelson- Morley 1,5 · Kennedy-Thorndike 7 · Time dilation / Doppler effect 2 · Universality Gravitational redshift 1 cavity – clock comparison 1,7 · Universality Gravitational redshift 2 clock-clock comparison 2,5 · Lense-Thirring effect via laser tracking 3 · Absolute gravitational redshift time transfer 1,4 · Perigee advance via laser tracking 3 · Newton potential via laser tracking 1 ·

ASTROD-Symp, Beijing, OPTIS Mission Outline 1 (Baseline scenario) to sun apogee km perigee km laser cavity frequency comparison atomic clock(s) frequency comb Michelson-Morley laser cavity frequency comparison Univ. grav. red-shift laser cavity frequency comparison atomic clock(s) frequency comb Kennedy-Thorndike ASTROD-Symp, Beijing,

OPTIS Mission Outline 2 Lense-Thirring effect (orbit precession) Perigee shift Test of Yukawa part in Newtonian potential High precision tracking by laser ranging in combination with drag free AOCS

ASTROD-Symp, Beijing, OPTIS Mission main characteristics Space conditions:  Long integration time  Large velocity changes  Large potential differences Noise reduction:  Drag-free AOCS ( < m/s Hz)  First time: combination of drag-free AOCS and laser ranging  Monolithic resonator  Systematic elimination of distortions New technologies in space:  Ultrastable lasers  Optical frequency comb  Resonators with narrow linewidth  Micro-Propulsion systems (e.g. FEEPs, Colloidal thruster)  Laser Link Platform  Ultrastable atomic clocks

ASTROD-Symp, Beijing, OPTIS Basic principle to measure the isotropy of c Usual 2 nd -order approximation:

ASTROD-Symp, Beijing, OPTIS Michelson-Morley (MM) experiment Phase shift measurement Brillet and Hall (1976) Best measurement on Earth: laser cavity frequency comparison

ASTROD-Symp, Beijing, OPTIS Kennedey-Thorndike (KT) experiment v v v v v0v0 Frequency change measurement: Braxmaier, Müller, Pradl, Mlynek, Peters, and Schiller (2002) Best measurement on Earth: laser cavity frequency comparison atomic clock(s) frequency comb

ASTROD-Symp, Beijing, OPTIS Test of Universality of Gravitational Red Shift (2) U1(r)U1(r) U2(r)U2(r) Frequency difference measurement: Best measurements: for H-maserCs-clock for 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 frequency comparison atomic clock(s) frequency comb

ASTROD-Symp, Beijing, OPTIS Effects measured by precise tracking Lense-Thirring effect: Precession rates of knots Perigee shift Test of the Newtonian potential

ASTROD-Symp, Beijing, OPTIS Mission Requirements  Variable spin rates(elimination of systematic errors) T Spin = 100 to 1,000 s  Cavity length variation requirement: δc/c < σ ΔL (T Spin ) / L <  Laser frequency lock instability: δc/c < σ lock (T Spin ) / f <  Temperature stability for cavities: ΔT random < 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 <  Residual acceleration on board spacecraft δa < m/s Hz  Laser ranging δr < 1mm

ASTROD-Symp, Beijing, OPTIS Key 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 = m Temperature stability: ΔT < K / √Hz but: for MM common mode rejection due to monolithic design: ΔT < K / √Hz Residual accelerations Gravity gradient: m/(s 2 ·  Hz)

ASTROD-Symp, Beijing, OPTIS Resonator model Elastic deformations under tidal forces analytical solution by S. Scheithauer and C. Lämmerzahl rΔr/RzΔz/L R6.2 · L1.6 · R6.5 · Displacements for a 7000 km orbit

ASTROD-Symp, Beijing, OPTIS OPTIS resonator (FEM analysis) calculated for a 7,000 km orbit

ASTROD-Symp, Beijing, OPTIS Mirror displacements during orbit relative displacement between 2 opposing mirrors displacements at mirror midpoints

ASTROD-Symp, Beijing, OPTIS Resonators and spin Relative mirror displacements dx on x-axis Orbital rotation around y-axis Spin around z-axis

ASTROD-Symp, Beijing, OPTIS Thermal gradients Thermal gradient along z - axis: K/L

ASTROD-Symp, Beijing, OPTIS Key technology: Lasers and electronics  Lasers: 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· s of cavity linewidth

ASTROD-Symp, Beijing, OPTIS Clocks Frequency [GHz]StabilityOperation in space H-maser GP-A, ACES, PHARAO, Galileo Ion clock GPS, SPACETIME Cs atomic clock Rb atomic clock GPS, Galileo Allan variance Integration time OPTIS requirement

ASTROD-Symp, Beijing, OPTIS Key technology: Frequency comb  Purpose: comparison of atomic clock frequency: Hz  with optical frequency: Hz  Accuracy: Hz

ASTROD-Symp, Beijing, OPTIS Spacecraft and orbit (baseline scenario)  Mass 250 kg  Power 250 W  High elliptic orbit  Period: 14 h  Inclination 63°  Shadow: 5 months without shadow 1 month with periods  Sun rad. press. 4.4 μN/m 2  Earth albedo rad. press. 1.2 μN/m 2  Laser ranging platform GTO HEO Apogee motor for orbit transfer FEEPs (???): ΔF = ± 0.1 μN F max = 100 μN + Reference sensor δa= m/(s 2 · √ Hz) In(Cs) Reservoir ONERA Cold gas thruster for coarse attitude control

ASTROD-Symp, Beijing, OPTIS OPTIS 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