IFSI: Experimental Gravitation (Detection of small displacements)

Transcription

1 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale di Astrofisica IFSI: Experimental Gravitation (Detection of small displacements) V. Iafolla,, E. Fiorenza,, D.M. Lucchesi, A. Morbidini,, S. Nozzoli, R. Peron, M. Persichini, F. Santoli, G. Vannaroni, M. Visco Istituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Via Fosso del Cavaliere, n. 100, Roma, Italy; ILIAS Roma 20 March 2006

2 GReAT: General Relativity Accuracy Test ISA: An accelerometer for the BepiColombo Mission to Mercury

3 GEOSTAR: gravimeter for deep-sea measurements G measurement with a one axis gravity gradiometer

4 The ISA accelerometer Actuator Capacitors Test Mass Detector Capacitors Reference Frame

5 Base concept of the accelerometer Base concept of the accelerometer f C Z T Q T m k a o n n r o b t Δ + β ω ω ω 2 4 ) ( 2 f T Q T m k a p o n r o b t Δ Ω + ω β ω ω 2 4 ) ( 2 no matching matching 2 2 o m r C ω α β = Ω = β ω tgδ Q p o e = Q m Q de Q / 4 = m Q T k a r o b bw ω

6 Accelerometer for space use Differential measurement in order to eliminate the seismic noise in the laboratory performed with two accelerometers with sensitive axes parallel. The residual flat noise is due to the electronics. The setup electronic (that used for the geophysics) was not the best one in order to reach the actual sensitivity of g / Hz. Anyway the level of the mechanical rejection is quite good.

7 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale di Astrofisica GReAT: General Relativity Accuracy Test EP test balloon experiment V. Iafolla,, E. Fiorenza,, D.M. Lucchesi, A. Morbidini,, S. Nozzoli, R. Peron, M. Persichini, F. Santoli, G. Vannaroni, M. Visco Istituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Via Fosso del Cavaliere, n. 100, Roma, Italy; Roma 20 March 2006

8 GReAT experiment The goal of the GReAT experiment is to test the Weak Equivalence Principle (WEP) with an accuracy of a few parts in 10 15, i.e., 2 orders of magnitude better than the actual ground based measurements: The differential accelerometer composed of two test masses of different material free falls inside a 3 m long cryostat dropped from a 40 km altitude balloon; the FF duration is about 30 s inside an evacuated capsule; the falling masses are part of a high sensitivity differential accelerometer with a sensitivity in detecting differential accelerations of about g / Hz at the liquid helium temperature (4.2 K);

9 GReAT experiment the differential accelerometer apparatus is spun about an horizontal axis at a frequency of 1 Hz (1ω) in order to modulate the signal during free fall; the experiment is isolated from external noise sources acting on the capsule, such as air drag; a non zero differential acceleration appearing at the rotation frequency will indicate a violation of the Equivalence Principle; once the instrument package reaches the capsule s floor, the capsule is decelerated by a parachute for retrieval and reflight; D = 1.4 m L = 6.5 m M = 1300 kg

10 GReAT experiment The liquid helium refrigeration is important to provide: low thermal noise; high thermal stability; low thermal gradients; high Q factors of the differential accelerometer detector; Small cryostat to refrigerate the instrument package (blue/purple); Open doors at bottom of cryostat; Instrument package span at 1 Hz before release into room temperature capsule;

11 GReAT experiment GReAT has several advantages with respect to other ground based experiments: full Earth s gravity signal: 1g ; acceleration noise of the FF detector g for a residual pressure of 10 6 mbar; drag shielded vertical FF; longer integration time;

12 GReAT experiment GReAT compared to the other proposed flying experiments to test the WEP: STEP: (drag free satellite) NASA; GG: (drag free satellite) INFN/ASI; MicroScope: (drag free satellite) CNES/ESA; GReAT: 5*10 15 (drag shielded capsule) ASI/NASA;

13 GReAT experiment The work of the teams involved in the GReAT experiment to test the WEP has been subdivided in the following main aspects: Free Fall system (SAO): cryogenic system (with Janis Research); release mechanism (cooling and clean release); room temperature electronics and detector power source; Detector (IFSI/CNR): achieving the required values (e.g., Q factor); attenuating initial transients; common mode rejection;

14 GReAT experiment Numerical simulations. 1EU 9 2 = 10 s FF simulation with the instrument package spun at 1 Hz including a possible violation of the WEP at the level of g. The violation signal at 1ω is well separated from the 2ω signals. 2ω contributions 1ω violation Spectral densities: Capsule gravity gradients; Earth s gravity gradients; Inertial gradients due to the vibrations of the capsule walls and to the platform, via the residual gas in the capsule; Reference gravity gradient: 10 2 EU Hz ;

15 Experimental results with a differential accelerometer prototype The first differential accelerometer prototype built at IFSI/CNR: Exploded view of the differential accelerometer prototype Sensitive axis direction Cross section of the (assembled) differential accelerometer prototype Spin axis direction Each sensing mass has to fixed capacitors plates for the signal pickup.

16 Experimental results with a differential accelerometer prototype Rejection of the common mode signals. Figure (b) shows that after calibrating for amplitude and phase a 10 4 attenuation is readily obtained for the differential signal. This level of attenuation is effective not only at the perturbation frequency of 0.15 Hz but also over a larger frequency band. (a) Spectra of individual and differential acceleration outputs: (a) after amplitude calibration 10 3 Spectra of individual and differential acceleration outputs: (b) (b) after amplitude and phase calibration 10 4 An attenuation of 10 4 or equivalently a common mode rejection factor of 10-4 meets the present requirement on the CMRF for the proposed tests of the WEP.

17 Experimental results with a differential accelerometer prototype Abatement of the natural dynamics excited by the instrument release into the capsule. R=50 MΩ τ1 =50 s Qt1=2900 R added Electrical scheme with resistance added to the feedback loop 1 Qt ω RC C E = M 2 o = + = β 2 β Qm Qe Qe ( ωorc) ω0 R removed τ2 =7.5 s Qt2=441 τ1 =50 s Qt1=2900

18 Experimental results with a differential accelerometer prototype Rejection of the common mode signals. One important characteristic of a differential accelerometer is its ability to reject perturbations that are not differential, i.e., common mode disturbances. This ability is quantified by the common mode rejection factor (CMRF).

19 New configuration of the differential accelerometer The second differential accelerometer prototype built at IFSI/CNR.

20 New Configuration of the differential accelerometer

21 New configuration of the differential accelerometer The second differential accelerometer prototype built at IFSI/CNR. Measurements to be performed with the new differential accelerometer prototype: in order to be able to perform laboratory measurements at the desired level of accuracy (actually g / Hz) it is necessary to build up a new fast electronics in order to acquire at high frequency over long periods. This is necessary to eliminate the laboratory aliasing effects; then it will be possible to start the studies in order to reduce the transient effects during the release phase; and the rejection of the common mode effects;

22 Advantages Reusability and easy access to experiment Low cost Strong gravity signal (i.e., 1 g) Noise level comparable to drag-free satellites Disadvantages Short integration time Conclusions In summary Estimated accuracy in testing the WEP several parts in with 95% confidence level Potential accuracy improvement of 2 orders of magnitude with respect to the state of the art

23 References V. Iafolla, S. Nozzoli, A. Mandiello High sensitive accelerometer for fundamental physics in space 2 nd Joint Meeting of the International Gravity Commission and the International Geoid Commission Trieste 7-12 settembre 1998 V. Iafolla, E.C. Lorenzini, V. Milyukov, and S. Nozzoli, "Gizero" Gizero: : New Facility for Gravitational Experiments in Free Fall." Gravitation & Cosmology,, Vol. 3, No. 2(10), , 160, V. Iafolla, S. Nozzoli, E.C. Lorenzini and V. Milyukov, Methodology and Instrumentation for Testing the Weak Equivalence Principle in Stratospheric Free fall. Review of Scientific Instruments,, Vol. 69, No. 12, , 4151, V. Iafolla, S. Nozzoli, E.C. Lorenzini, I.I. Lorenzini and V. Milyukov, Development s of the general relativity accuracy test (GReAT): a ground-based experiment to test the weak equivalence Classical and Quantum Gravity F. Fuligni,, V. Iafolla and S. Nozzoli, Experimental Gravitation and Geophysics. Il Nuovo Cimento,, Vol. 20C, No. 5, F. Fuligni and V. Iafolla, Measurement of Small Forces in the Physics of Gravitation and Geophysics. ophysics. Il Nuovo Cimento,, Vol. 20C, No. 5, E.C. Lorenzini, F. Fuligni,, J. Zielinski, M.L. Cosmo, M.D. Grossi,, V. Iafolla and T. Rothman, "Balloon- Released Experiments in Gravitational Physics", Advances in Space Research,, Vol. 14, No. 2, (2)113- (2)118, E.C. Lorenzini, I.I. Shapiro, F. Fuligni,, V. Iafolla, M.L. Cosmo, M.D. Grossi,, P.N. Cheimets and J.B. Zielinski, "Test of the Weak Equivalence Principle in an Einstein n Elevator." Il Nuovo Cimento,, Vol. 109B, No. 11, , 1212, F. Sanso, A. Albertella,, G. Bianco,, A. Della Torre,, M. Fermi, V. Iafolla, S. Nozzoli, A. Lenti,, F. Migliaccio, A. Milani, A. Rossi. Sage: An Italian Project of Satellite Accelerometry Towards an Integrated Global Geodetic Observing System (IGGOS) Munich, Germany October 1998 S. Mazza, A. Morelli; ING, Roma Rumore Sismico a Larga Banda.

24 Release system

25 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica ISA (ITALIAN SPRING ACCELEROMETER): AN ACCELEROMETER TO MEASURE THE INERTIAL ACCELERATIONS ACTING ON THE MPO. Iafolla V.; Fiorenza E.; Lucchesi D. M.; Nozzoli S.; Fois M.; Morbidini A.; Peron R. Ravenna M.; Santoli F.; Vannaroni G.; Visco M. V. Iafolla

26 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica BepiColombo Radio Science Experiments ISA (Italian Spring Accelerometer) The ISA (Italian Spring Accelerometer) accelerometer developed at IFSI/CNR considered to fly on board the MPO. It is a three axes accelerometer. The key role of the accelerometer is to remove from the list of unknowns the non gravitational perturbations,, i.e., the strong non conservative accelerations on the MPO produced by the Sun visible radiation and by Mercury infrared radiation; To fulfil the RSE the non gravitational accelerations must be limited to a level of 10-9 g, which has been taken as the accelerometer accuracy,, in the frequency band 3* Hz; Direct solar radiation pressure: the transversal acceleration and its spectrum V. Iafolla

27 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica Acceleration acting on ISA The acceleration on a point P (ISA proof mass) close to the MPO COM is: & R r r r r r r r r r &r r = g R ω ω R &r ω R 2 ω R A ( ) ( ) ( ) NGP Acceleration due to Mercury gravity field gradients Z Centrifugal acceleration Angular acceleration Coriolis acceleration Non Gravitational accelerations X Inside the MPO frame λ ϑ R r ISA proof mass Y g r ω r &r ω R r = Mercury gravity; = MPO angular rate: = MPO angular acceleration; = MPO proof mass vector; V. Iafolla

28 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica RSE total noise V. Iafolla

29 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica ISA accuracy requirement inside the frequency band Frequency Hz Acceleration values 2 m / s / Hz V. Iafolla

30 ISA (Italian Spring Accelerometer) Three-axis

31 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica Requirements on the angular rate and angular acceleration for the following fixed values of the position of the spacecraft COM: X t = 30 mm, Y t = 20 mm and Z t = 40 mm. δω δ & ω Case A) Case B) rad s Hz rad s Hz rad 2 s Hz rad 2 s Hz Case A: com COM Case B: com +20 cm COM V. Iafolla

32 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica Vibrational random noise on board the MPO inside the frequency bandb Frequency Hz Acceleration values ( m / s 2 / Hz ) Micro-vibration random noise on board the MPO outside the frequency band V. Iafolla

33 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica ISA thermal system overview One of the main characteristics for the accelerometer to be considered in the BepiColombo mission to Mercury is its thermal stability, i.e., the immunity of the accelerometer to temperature variations: over one orbital period (2.3 h) of the MPO; ±2 C ±12.5 C over one sideral period (44 days) of Mercury; In the actual version of the ISA accelerometer the thermal stability is: Random noise; 5 10 That is a temperature change of 1 degree produces a voltage output equivalent to: g 5 10 m s 4 C/ Hz 8 g o / C V. Iafolla

34 Istituto di Fisica dello Spazio Interplanetario ACCELEROMETER PAKAGES THERMAL INSULATOR Istituto Nazionale Di Astrofisica ISA thermal system overview COVER_BOX OVEN BOX GL=0,3 QI=0.078W GL=0,003 GR=0,0005 GR=0,008 GR=0,0067 GL=5 ENVIROMENT α=ε=0.9 CONTROL ELECTRONIC QI = 3.7 W OVEN_PCB GR=0,0028 PCB QI=0.88W GL=0.03 GL=0,5 GR=0,014 GL=0,8 BOTTOM_BOX GL=3 GR=0,05 SPACECRAFT ISA Thermal Mathematical model V. Iafolla

35 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica ISA DETECTOR ASSY OVERVIEW External Shield ISA Detector Assy Electrical I/F Accelerometer Thermal Insulation Internal Thermal shield Accelerometer Package V. Iafolla

36 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica ISA Error Budget: Pseudo Sinusoidal Contributions Type Due to Spectral requirement Error % content on A 0 Gravitygradients and ½P Orbital period P n Apparent 0 0 forces R r r Δ 0 & Orbital period P ; ΔR t ( t) and ½P 85%A 0 Thermal Orbital period P 2 C effects and ½P Δ T 15%A 0 Components Misalignment Orbital period P coupling angle and ½P Δα Negligible Total 100%A 0 V. Iafolla

37 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica ISA Error Budget: Random Contributions Type Due to Spectral content r r Apparent forces R ; R () t Thermal effects Noise on the MPO MPO COM displacement Components coupling requirement on 0 t Random δω ; ω Error percent δ & 60%A 0 o 4 C Hz Random Δ T 30%A 0 Movements due to the HGA, fuel sloshing ecc. Movements due to the HGA and fuel consumption ecc. Random 10%A 0 r Random Δ () t 70%A 0 Misalignment angle Random δα Negligible ISA intrinsic noise Random Negligible Total (not correlated noise) <100%A 0 R t V. Iafolla

38 MORE: Science Goals Spherical harmonic coefficients of the gravity field of the planet up to degree and order 25. Degree 2 (C 20 and C 22 ) with 10-9 accuracy (Signal/Noise Ratio 10 4 ) Degree 10 with SNR 300 Degree 20 with SNR 10 Love number k 2 with SNR 50. Obliquity of the planet to an accuracy of 4 arcsec (40 m on surface needs also SYMBIO-SYS) SYS) Amplitude of physical librations in longitude to 4 arcsec (40 m on surface needs SYMBIO-SYS). SYS). C m /C (ratio between mantle and planet moment of inertia) to 0.05 or better C/MR 2 to or better.

39 MORE: Science Goals Spacecraft position in a Mercury-centric centric frame to 10 cm 1m (depending on the tracking geometry) Planetary figure, including mean radius, polar radius and equatorial radius to 1 part in 10 7 (by combining MORE and BELA laser altimeter data ). Geoid surface to 10 cm over spatial scales of 300 km. Topography of the planet to the accuracy of the laser altimeter (in combination with BELA). Position of Mercury in a solar system baricentric frame to better than 10 cm. PN parameter γ,, controlling the deflection of light and the time delay of ranging signals to 2.5*10-6 PN parameter β,, controlling the relativistic advance of Mercury s perihelion, to 5*10-6 PN parameter η (controlling the gravitational self-energy energy contribution to the gravitational mass to 2*10-5 The gravitational oblateness of the Sun (J 2 )to 2*10-9 The time variation of the gravitational constant (d(ln( d(lng)/dt) ) to 3*10-13 years -1

40 Geophysical Measurements Horizontal component of the seismic noise recorded at the MEDNET stations Line of minimum noise g / Hz Vertical component of the seismic noise recorded at the MEDNET stations Line of minimum noise 7*10 11 g / Hz

41 Geophysical Measurements Cryogenic Gravimeter Nuclear Power Station of Brasimane

42 Geophysical Measurements 1000 Y(T) Y( s) = F( s) X( s) Trieste Grotta Gigante 2 a ωn Ys () = 2 2 X() s s + 2ξω s+ ω n n T (seconds)

43 Istituto Nazionale di Fisica Nucleare (INFN) Gran Sasso Interferometer

44 ISA laboratory calibrations

45 Geophysical Measurements x 10-3 Misure GEOSTAR Accelerazione [g] Earthquakes 13 gen :33:29:22 Off Coast of Central America Registrazione Gravimetro Geostar Ustica Long time registration at Gran Sasso 25 May July Tempo giorni dal 2001

46 Long time registration at Gran Sasso 25 May July 98

47 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica Gravity Gravimeter for Deep-Sea Measurements and Sergio Nozzoli Istituto di Fisica dello Spazio Interplanetario Rome, Italy

48 Gravimeter General Characteristics Sensitivity 10 9 g / Hz Frequency Range Hz Power dissipation 300mW Volume 10X10X10 cm Weight 2Kg Benthos VacuSealed

49 GEOSTAR Platform

50 Mechanical Arrangement

51 Mechanical Oscillator

52 Transfer Function

53 Gravimeter Calibration

54

55 Mechanics Electronics Temperature Time Problems of Dynamic d 0 = 100μ m A / D 1 4 b it 1 0 K H z Δg Topp = 12C ΔTday = 10 C = 10 ΔT 10 5 g/ day 4 4 g C o Δa Δx min min g 8 v = e = 10 V min Pressure Sensitivity = = 10 /( 2π14) = 12. * 10 n * 10 g/ atm ΔP = 10 mbar m day Frequency Range Hz

56 Signal Variation VS Temperature

57 Low Dissipation Electronics 1 Low Noise Amplifier Demodulator 30mW 150mW

58 Low Dissipation Electronics 2 Multiplexer A/D 10mW 50mW RS232 10mW Microcontroller 10mW

59 Istituto di Fisica dello Spazio Interplanetario Istituto Nazionale Di Astrofisica G measurement with a gradiometer V. Iafolla, S. Nozzoli, E. Fiorenza, M. Ravenna Istituto di Fisica dello Spazio Interplanetario CNR Roma, Italy

60 CODATA value: Value of the gravitational constant G 11 (6.673 ± 0.010) 10 m Kg Corresponding uncertainty : 1500 ppm 3 1 sec 2 Gundlach, J. H. and Merkwitz, S.M. Phys. Rew. Lett. 85, (2000) G = ( ± )*10 11 m 3 /( Kg s 2 ) Corresponding uncertainty : 14 ppm

61 Torsion Balances for the measure of G

62 Istituto di Fisica dello Spazio Interplanetario CNR Roma, Italy One axis Gravity Gradiometer

63 Experimental set-up

64 Gradiometer calibration

65 Experimental set-up x 10-9 PSD Momentum [Nm pk] Momentum [Nm] Time [sec] Freq [Hz] κt =1.7 N m / rad M ϑ = = 2 ω I 0 M κ t θ min = = rad (8h int. time) rad / Hz

66 Comparison between signal and noise θ min 8 10 ext = rad / Hz 2 10 g / Hz acceleration(g/sqrt(hz)) freq(hz) Rumore elettronica Rumore con simulacro di rotore Rumore con rotore in azione

67 Gradiometer transfer function Q=3 Q=0.1

68 Gradiometer transfer function 2 ϑ / ϑ = s /( s + s ω / Q + ω out in Q = 10 2 ω = 2 π 3.5 rad / s )