Gravitational Physics. Experiments in Space. Sasha Buchman Stanford University. Lisbon & Porto, STAR 2015 Space Time Asymmetry Research

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1 Gravitational Physics STAR 2015 Space Time Asymmetry Research Experiments in Space Sasha Buchman Stanford University Lisbon & Porto, 2010 GP-B, Relativity Mission, Gravity Probe B LISA, 2025 Laser Interferometer Space Antenna

2 George Bernard Shaw 1930 Napoleon and other great men of his type, they were makers of empire, but there is an order of men who get beyond that. They are not makers of empires, but they are makers of universes. And when they have made those universes, their hands are unstained by the blood of any human being on earth. Ptolemy made a universe which lasted 1400 years, Newton also made a universe which has lasted 300 years, Einstein has made a universe and I can t tell you how long that will last

3 Outline Gravity GP-B Why Test Gravity? How To Test Gravity? Why Space? Electro Magnetism Strong Nuclear Force Weak Nuclear Force Balloon experiment LISA General Relativity, GP-B Lorentz Invariance, STAR Gravitational Waves, LISA STAR

4 How Well Is GR Tested GM/c 2 R << 1 Sun ~ 2 x 10-6 ; Earth ~ 7 x ; 1 m W sphere ~ 5 x Einstein's 2½ tests Perihelion of Mercury, light deflection, redshift ( ½ test) Test enabled by new technologies since 1960 Clocks, electromagnetic waves, massive bodies Observations [O] vs. controlled physics experiments [E] New non-null tests Shapiro time delay [O] Geodetic effect by laser lunar ranging [O] Binary pulsar, gravitational wave damping [O] Gravity Probe A [E] Gravity Probe B [E] The Eddington PPN formalism & new null tests LLR, Nordtvedt effect restricts scalar-tensor theories [O] Earth tides, Will effect eliminates Whitehead's theory [O] GW astronomy [50 years since J. Weber detector] Einstein 2½ Tests The General Theory of Relativity: Is THE Accepted Theory of Gravitation Agrees to Better than with Experimental Results

5 Why Verify GR? General Relativity = Present Theory of Gravity Mathematically Consistent Agrees with Observation (so far) Unified Physics? Standard Model: Quantum Gauge Theories GR cannot be quantized Gravity Partial steps toward Grand Unification Strings/super symmetry Damour - Polyakov Experimentation and Observation Strong Nuclear Force Electro Magnetism Weak Nuclear Force

6 Problems With GR? Astronomical Observations A Dark Universe An Expanding Universe Interesting Phenomena Solar System Observations? Pioneer Anomaly Fly-by Anomaly Short Scale Deviations?? Expansion of the Universe Over Time NGC 6251 Power W (10 12 Suns) Jet aligned 10 7 light years GP-B science

7 How To Test Gravity? Astronomical Observations CMB Polarization: WMAP, BOOMERANG X Ray Polarization: GEMS Pulsar Timing Space Experiments Gravitational Waves: LISA, DECIGO, BBO Rotational Effects: GP-B Space-Time Isotropy: STAR, OPTIS Equivalence Principle: MICROSCOPE, STEP Laboratory Short Scale Deviations Gravitational Waves: LIGO, VIRGO, Antennas High Frequency GW Boomerang WMAP Drag-free Test Mass High-Finesse ULE Cavity Resonators AGIS Atomic Gravitational Wave Interferometric Sensor Gravity and Extreme Magnetism (GEMS)

8 Why Go To Space? Seismic f < 10Hz Low gravity Varying gravitational potential Long baselines Fast varying velocity vector h vs. 0.4 km/s at 24 h Long measurement times Launch environment Thermal environment Cost and duration Reliability; one shot Communications bandwidth

9 Drag-Free Technology Control Spacecraft to follow an inertial sensor Reduce disturbances in measurement band Aerodynamic drag Magnetic torques Gravity Gradient torques Radiation Pressure GP-B Flight Gyroscope 2004 TRIAD Sensor 1972

10 Why Test Gravity? How To Test Gravity? Why Space? General Relativity, GP-B

11 The Relativity Mission Concept "No mission could be simpler than Gravity Probe B. just a star, a telescope, and a spinning sphere." William Fairbank Controlled experiment PPN Parameters = 1 in GR curvature of space 1 GM R v c R Geodetic Effect Space-time curvature de Sitter (1916) 1 GI 3R 1 R e e 4 2c R R Frame Dragging Rotating matter drags space-time Pugh and Schiff (1959, 1960) 1 = 0 in GR preferred frame effect

12 The GP-B Challenge Gyroscope (G) 10 6 better than best 'modeled' inertial navigation gyros Telescope (T) 10 3 better than best prior star trackers Gyro Readout calibrated to parts in 10 5 G T <1 marc-s subtraction within pointing range Basis for 10 6 advance in gyro performance Space reduced support force, "drag-free" roll about line of sight to star Cryogenics magnetic readout & shielding thermal & mechanical stability ultra-high vacuum technology

13 Main Experimental Features Electrostatically suspended quartz gyroscopes with He spin-up < 0.3 marcsec/yr drift Telescope with cryogenic photo detector read-out pointed <0.1 marcsec measurement, < 34 marcsec/ Hz pointing Drag free satellite in 642 km polar orbit, rolling at 5 mhz <10-10 g, <10-12 g transverse Cryogenic experiment 2K superfluid helium >18 month lifetime London moment based read-out with dc SQUID amplifiers <200 marcs/ Hz, < J/Hz Superconducting magnetic shielding < G, >10 12 total ac attenuation All (almost) requirements met

14 The GP-B Science Instrument SQUID Magnetometer (1 of 4) Measurement noise: ~ 200 marcs/ Hz Guide star IM Pegasi Gyros 1 & 2 Star tracking telescope Quartz block Gyros 3 & 4 Mounting flange SIA Field of View: ±60 arc-sec. Meas. noise: ~ 34 marcs/ Hz

15 GP-B Systems Probe Test of probe in dewar Thermovac test of spacecraft

16 GP-B Launch April 20, 2004

17 The GP-B Gyroscopes Electrical Suspension He Gas Spin-up Magnetic Readout Cryogenic Operation Fused quartz rotor R/R < 10-6 Quartz housing R/R < 10-5 Electrostatic suspension 10-9 g to 1 g Capacitive positioning <0.3 nm at roll He gas spin-up Hz UV charge control <15 pc

18 GP-B Science Mission 3 Phases A. Initial Orbit Checkout days Re-verification of all ground calibrations [scale factors, tempco s etc.] Disturbance measurements on gyros at low spin speed B. Science Phase days Exploiting the built-in checks [Nature's helpful variations] C. Post-experiment tests - 46 days Refined calibrations through deliberate enhancement of disturbances, etc. [ learning the lesson from Harrison & Cavendish] Detailed calibration & data consistency checks eliminated many potential error sources & confirmed many pre-launch predictions, but Anomaly 1 (Phase A, B) Polhode-rate variations affect C g determinations Anomaly 2 (Phase B, C) Larger than expected misalignment torques

19 Hours EW orientation, s EW (arcsec) Drift Rate (as/day) 3 Data Analysis Issues A. Polhode period variations affect scale factor (C g ) determinations Observed in early science phase B. Misalignment torques: req Observed in post-science calibration Magnitude of Drift Rate vs. Angle of Misalignment Gyro 1 Gyro 2 Gyro 3 Gyro 4 C. Roll-polhode resonance torques Observed in data analysis phase Gyro 1 Polhode Period Time (days from Day #1; Apr. 20, 2004) Angle of Misalignment (degrees) Gyro 2 per orbit orientation s EW res. m All due to one physical cause: The Patch Effect Date (2005)

20 GP-B Performance marcsec/yr Roll averaged 1,000 to 2,500 marcs/yr Apparent linear drift about 500 marcs/yr Repeat events to 200 marcs MISALIGNMENT 1000 LINEAR DRIFTS RESONANCE ,606 Geodetic effect 39.0 Frame dragging effect DESIGN GP-B Requirement 0.01

21 Relativity & Newtonian Torque Model Relativity Misalignment torque Roll-polhode resonance torque Add misalignment torque term to equations of motion Add roll-polhode resonance term to equations of motion

22 Effects of Patch Potentials 8 Observed Effects 1. Coupling to GSS Z axis force 2. At zero frequency 3. At polhode harmonics Torques 4. Misalignment 5. Resonance Dissipation mechanisms 6. Polhode damping 7. Spin-down 8. Charge meas. bias Affect gyro performance Affects read-out performance Observations explained by patch effect of ~ mv on rotor and housing

23 Raw Flight Data (Gyro 2) Apply Torque Model

24 Newtonian Effects Removed EW orientation (arcsec) NS orientation (arcsec) Gyro 2, orientations Newtonian torques NS uniform drift Jan 8 Jan 28 Feb 17 Mar 9 Mar 29 Apr 18 May 8 EW uniform drift +1 1 Jan 8 Jan 28 Feb 17 Mar 9 Mar 29 Apr 18 May 8 date (2004)

25 Gyro 1 Segments 95% confidence ellipses Consistency Seg. 2-3 Seg. 10 Seg. 5,6,9,10 Seg. 9 Seg. 5-6 NS / EW observability varies due to annual aberration

26 Four-Gyroscope Consistency 95% confidence ellipses Gyro 2 Gyro 1 Gyro 4 Gyros 1,2,3,4 Gyro 3

27 marcsec/yr marcsec/yr Gyroscope Performance 1 marcsec/yr = deg/hr = rad/sec Electrostatic gyro uncompensated (10-1 deg/hr) Spacecraft gyros (3x10-3 deg/hr) Laser gyro 39 Frame dragging effect (10-3 deg/hr) Expected GP-B ,606 Geodetic effect ~ 1,000 Patch effects Electrostatic gyro with modeling (10-5 deg/hr) GP-B Gyro Design improvement over previous gyroscopes

28 GP-B Summary GP-B worked very well All systems performed beyond expectations Anomalous effects Explained by patches on rotor and housing Systematic errors ~ 10 marcs Complex experiments in space work Surprises can be overcome: patch modeling

29 Why Test Gravity? How To Test Gravity? Why Space? General Relativity, GP-B Lorentz Invariance, STAR

30 Gravitational Science on Small Satellites GOALS Gravitational experiments (+others?) Lorentz invariance Fundamental constants in variable potential Small satellite missions 180 kg, 150W 60 M$, < 6 years Education PhD thesis, undergraduates Capability continuity IMPLEMENTATION STAR program 3-5 projects Start 2009, first launch 2015

31 Why Measure c Invariance? Colladay and Kostelecky (1997) The natural scale for a fundamental theory including gravity is governed by the Planck mass M P, which is about 17 orders of magnitude greater than the electroweak scale m W associated with the standard model. This suggests that observable experimental signals from a fundamental theory might be expected to be suppressed by some power of the ratio: r m W M P ~ STAR s one part in sensitivity could close that gap. STAR = Space-Time Asymmetry Research

32 Kennedy-Thorndike 100 gain over the best KT measurement KT STAR Mission Objectives Measure the boost anisotropy of the velocity of light to Derive KT coefficient to the corresponding resolution, ~ 7x10-19 Readout Description Orbital velocity varies with respect to CMB. If c depends on v S relative to CMB, the resonant frequency of the cavities changes. Signal at orbital period T KT (T KT 100 min) STAR compares the frequency of cavity to wavelength of molecular-iodine stabilized laser as absolute frequency reference. R.J. Kennedy E.M. Thorndike History of KT resolution

33 Lorentz Invariance 2 c( v, ) v v 1 1 ( 1 2 ) 2 c c sin c 2 KT MM 2 2 Lorentz contraction parameter time dilation parameter tests for transverse contraction GR: c( ) /c = 1, KT = MM = 0 CMB: preferred frame (v CMB /c) 2 = 10-6 Targeted Outcomes for Astrophysics 1. Test the validity of Einstein s General Theory of Relativity; 2. Investigate the nature of space-time through tests of fundamental symmetries; (e.g., is the speed of light truly a constant?) NASA Science Plan Test space/time symmetry 2. Improve understanding of cosmological parameters in Standard Model Extension (SME)

34 Component of SME Beat Signal

35 Main Systems Commercially available components reduce risk and keep STAR low-cost Multi-Layer Thermal Shield for Sub-µK Thermal Stability of Enclosure High-Finesse ULE Cavity Resonators Iodine Gas Cell Absolute Frequency Reference 1064 nm Nd:YAG Laser Frequency Shifters

36 Major Mission Characteristics Measure the anisotropy of the velocity of light to Primary data product: map of local values of c Orbit: most precessing sun-synchronous LEO s Launch vehicle: Secondary payload Altitude: 650 km Mission duration: One year Launch: late 2015 Cost: $ 50M Spacecraft structure Spacecraft in orbit concept 165 kg 110 W LISA technologies Iodine clocks Optical cavities Thermal enclosure Frequency doublers Electronics Lasers/Optics Deck Cavities & Core Optics Payload layout

37 Why Test Gravity? How To Test Gravity? Why Space? General Relativity, GP-B Lorentz Invariance, STAR Gravitational Waves, LISA

38 Gravitational Waves (GW) In the weak field approximation GW can be represented as a perturbation to the Minkowski flat space-time: g h g Minkowski space perturbed by gravitational waves Minkowski space h gravitational waves perturbation Using the transverse traceless gauge the field equation for h is: h c 2 2 t 2 G c S 4 S Energy densities and stresses In GR h results in two plane waves with polarizations at 45 : h a ˆ h t z b ˆ c h t z c

39 Gravitational Radiation: The Quadrup The quadrupole is the first gravitational radiation moment The leading gravitational radiation term is h 2G 4 c.. 1 Q r h Minkowski space perturbation G gravitational constant r distance to the source Q trace-free quadrupole tensor Space is stiff (2G/c 4 = s 2 kg -1 m -1 ) The GW perturbation h propagates as 1/r

40 LISA Concept Three spacecraft in triangular formation separated by 5 million km Spacecraft have constant solar illumination Formation trails Earth by 20 Orbit position and velocity modulate GW amplitude and phase From amplitude and phase LISA determines direction to source to <1

41 The LISA Gravitational-Wave Sky

42 Gravitational Waves Through Time

43 The GW Spectrum HF EM Detectors Bar Detectors BBO DECIGO

44 The Earth Based GW Detectors GW Detection by

45 LISA Systems Test mass Optical bench Y tube Payload Spacecraft Propulsion module Launch configuration

46 LISA Path Finder Development Torsion balance Housing GRS Optical components Optical bench

47 Two Optical Benches in Spacecraft

48 Space GW Missions LPF 2013 LISA 2025 LISA II 20?? Arms are 50,000 km

49 Conclusions GR most likely needs updating GP-B shows that complex experiments in space do work GW space observatory should be functional next decade STAR could see first LIV this decade Space science can and will be done on small missions Gravitational experiments are taking off in the next decade

50 Looking to the Future The towering figure of Einstein provides a tempting target for physicists of all stripes. He would perhaps look with approval on these efforts to go beyond his theories. The Search for Relativity Violations Alan Kostelecky Scientific American 2004

51

52 GP-B Back-up

53 Gravitoelectric and Gravitomagnetic Viewpoint Similarity between electromagnetism and General Relativity in weak field and slow motion limit Space-Time Newtonian EM Gravito-EM Rotational Metric Analog Analog Analog Effect g 00 V E g 1/3 G g 0i No analog A i B g FD g ij No analog No analog No analog 2/3 G

54 Near Zeros Technologies Seven Near Zeros for Gyro Performance Rotor inhomogeneities < 10-6 met Rotor asphericity < 10 nm met "Drag-free" (cross track) < g met Magnetic field < 10-6 G met Pressure < torr met Electric charge < 15 pc met Electric dipole 2 < 0.1 V m issue

55 Radius Homogeneity Sphericity Mass unbalance Rotor Fabrication 1.9 cm < 2 ppm < 1 ppm < 1 ppm Holder for Quartz Homogeneity Measurement Met All Requirements I/I < Nb Film Uniformity <2% Surface Profile Profile of Optical Path Difference - nm Polishing System Roundness Measurement Min=9 nm Max-Min =19 nm Max=10 nm Surface Profile Scaled to Earth Size

56 Housing Fabrication Radius 1.9 cm Sphericity < 10 ppm 6 Electrodes in 3 Orthogonal Pairs 5 Turn Read-out Loop Channel and Ti Nozzle for Spin-up 7-layer Ti-Cu Electrode Coating 3-layer Ti-Cu-Ti Support and Spin-up Lands Coatings Ti Film For Bare Quartz Spin-up Half Met All Requirements Fused-Quartz Gyroscope Housing Read-out Half Lands Coatings Electrodes Coatings Three Layer Film SEM Micrograph Seven Layer Film SEM Micrograph Gyro to Spacer Assembly Gyro insertion in Quartz Block

57 Spin rate (Hz) S - N (arc-sec) Spin-up and Alignment Spin speed and spin down meet requirements Differential Pumping Requirement Spin channel ~ 10 torr (sonic velocity) Electrode area < 10-3 torr Torque Switching Requirement T s, T r - spin & residual torques t s - spin time; Ω 0 - drift requirement T r / T s < Ω 0 t s ~ Gyroscopes spun to Hz Gyro # f (Hz) df/dt (μhz/hr) saa-summary-plot.m <GSV median> Contour interval = 25 arc-sec Gyro1 Gyro2 Gyro3 Gyro First Science Mission Levitation Gyro 1 Gyro 2 Gyro 3 Gyro Time (hours) Spin-up of one gyro causes spin down of other ones: Gyro 1 last W - E (arc-sec) Spin Alignment to 10 arcsec

58 GP-B on Jon Stewart s Daily Show

59 GP-B in Flight GOOD Gyroscopes better than ground SQUID noise meets spec Trapped magnetic flux meets spec Charge control ~ meets spec Position and stability meet spec τ ~ 7200 to yr meet spec Telescope Meets spec Dewar 20 months hold meets spec Orbit within 100 m of ideal LESS THAN IDEAL Torques Misalignment torque Resonance torque Other Polhode rate variation Segmented data Interference from ECU SRE scale factor New Challenge Systematics & data grading

60 Full Model Results (Dec 08) N-S (Geodetic) E-W (Frame-dragging) G1 G2 G3 G4 (note: different y-axis scale for N-S vs. E-W)

61 STAR Back-up

62 Michelson Morley Secondary MM STAR Mission Objectives Measure the anisotropy of c to Derive the MM coefficient to ~ Derive the generalized coefficients of LIV boost independent: < 7x10-17 boost dependent: ~ Readout Description Compare the resonant frequencies of two orthogonal high-finesse optical cavities Signal at 1/2 T MM (T MM = 2 20 min) Configuration conceptually similar to MM COSMIC MICROWAVE BACKGROUND History of MM resolution

63 LISA Back-up

64 Gravitational and Electromagnetic Waves Gravitational Electromagnetic Source Coherent mass acceleration Incoherent charge acceleration Propagation Space-time oscillations (2 polarizations at 45 ) EM fields in space-time (2 polarizations at 90 ) Attenuation None Scattering, absorption Frequency <10 khz (possibly higher) >10MHz (radio to gamma)

65 Strain [Hz -1/2 ] The DECIGO Project Japanese Space Agency LISA Terrestrial Detectors (e.g. LCGT) DECIGO (Sensitivity: Arbitrary) Frequency [Hz]

66 Advanced Concepts - Stanford Single spherical proof mass (PM) per S/C LPF (LISA Pathfinder): 2 cubic ones Non constraint GRS; 0 of 6 DF (deg. freedom) control LPF: 9 of 12 DF control Gravitational sensor separation from S/C Interferometry LPF: implemented Fiber utilization LPF: discrete optics Reflective optics d /dl 0.1 d /dn LPF: transmissive optics d /dn 10 d /dl Signal LO GRS with double sided grating for interferometer and PM reference

67 Bench Interferometer Configuration (Example: Polarization Sensitive Grating Beam Splitter) Highly simplified structure compared with transmissive optics Detector In from Telescope Out to Telescope Proof Mass Grating Laser (Other diffraction orders with detectors not drawn for simplicity)

68 Patent pending Grating Cavity Displacement Sensing Sensitivity better than 10 pm/ Hz Low-Finesse Littrow Cavities as Displacement Sensors Goals for Sensor High precision: 1 pm / Hz in LISA band Low power: Less than 20 W optical power Compact: Fiber delivery and read-out K.-X. Sun, G. Allen, S. Buchman, D. DeBra, and R. Byer, Classical and Quantum Gravity 22, S287 S296 (2005) Preliminary Results: 10 pm/ Hz f > 3 khz

69 Patent pending Grating Angular Sensor for Space Missions Simple construction No extra optics No other uncertainty and noise Experimental Setup Ke-Xun Sun, Sasha Buchman, Robert L. Byer, Grating Angle Magnification Enhanced Angular and Integrated Sensors for LISA Applications, Journal of Physics CS, 32: , 2006.

70 Optical Position Determination: Simulation Spinning sphere, 10 Hz 2 Dimensional 6 Optical sensors Experimental laser noise 50 nm position noise 50 nm surface roughness 1024 map size f noise /f spin = pm/ Hz position noise

71 Utilizing Launch Margins Technology Demonstrations for the Gravitational Reference Sensor - GRS Stanford NANOSAT AMES GENESAT UV LED MINISAT, The Mini Satellites for GRS Technologies The Program Frequent launches on ride-along platforms Standard low cost bus configurations month project duration The Benefits New science: Physical, Life, Engineering Critical technology demonstrations Fast advance of NASA mission objectives Train engineers and scientists for the future Program Implementation Collaboration: AMES, Stanford University Continuity: 1 to 2 missions per year Total cost per mission: 5 million dollars