1. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla, E. Fiorenza, C.Lefevre, D.M. Lucchesi, A. Morbidini, S. Nozzoli, R. Peron, M. Persichini, A. Reale, F. Santoli Istituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Roma, Italy The BepiColombo mission to planet Mercury and the fundamental role of ISA accelerometer for the Radio Science Experiments 13 September 2007 1Iafolla et al. - ERE07 Encuentros Relativistas Españoles - Spanish Relativity Meeting ERE07 Puerto de la Cruz, Tenerife, Spain

2. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario 13 September 2007 Iafolla et al. - ERE072 Mercury From Andreas Cellarius, Harmonia Macrocosmica, plate 8 Photo © NASA

3. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario BepiColombo space mission objectives The space mission BepiColombo (BC), one of the Cornerstones of the European Space Agency (ESA), aims to perform (Grard & Balogh, 2001; Iess & Boscagli 2001; Milani et al., 2001, 2002): 1.a detailed study of the planet Mercury and its environment 2.and to test Einsteins General Relativity (GR) to an unprecedented level of accuracy Launch epoch August 2013 + 1 year of nominal duration Arrival epoch August 2019 Launch on Soyuz 2-1B Fregat-M 13 September 2007 3Iafolla et al. - ERE07

4. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario The accurate knowledge of the Mercury Planetary Orbiter (MPO) orbit represents the way to achieve a large part of these targets: The MPO will be characterized by a polar orbit around Mercury, with a semi–major axis of about 3389 km and a relatively high eccentricity of 0.162 The MPO will be a 3–axis stabilized spacecraft, Nadir pointing, and equipped with a complete set of instruments in order to perform Radio Science Experiments (RSE) BepiColombo space mission objectives 13 September 2007 4Iafolla et al. - ERE07

5. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario 4001500 MPO MPO 400 1500 km polar orbit Nadir pointing BepiColombo space mission objectives 13 September 2007 5Iafolla et al. - ERE07 a = 3389 km e = 0.162 I = 90° P = 8355 s degrees/day

6. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario The RSE, represents a complex mix of measurements and scientific objectives and, very interesting, it is not possible to separate them neatly in independent experiments. However, we can distinguish: 1)a gravimetry experiment 2)a rotation experiment 3)a relativity experiment Basically, on–board the MPO, the instruments used for these experiments are: Ka–band Transponder Ka–band Transponder Star–Tracker Star–Tracker High Resolution Camera High Resolution Camera Accelerometer Accelerometer BepiColombo Radio Science Experiments 13 September 2007 6Iafolla et al. - ERE07

7. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario BepiColombo Radio Science Experiments Objectives The global gravity field of Mercury and its temporal variations due to solar tides (in order to constrain the internal structure of the planet) The local gravity anomalies (in order to constrain the mantle structure of the planet and the interface between mantle and crust) The rotation state of Mercury (in order to constrain the size and the physical state of the core of the planet) The orbit of the Mercury center–of–mass around the Sun (in order to improve the determination of the parametrized post–Newtonian (PPN) parameters of GR) 13 September 2007 7Iafolla et al. - ERE07

8. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario BepiColombo Radio Science Experiments Kinds of Measurements Range and range–rate derivations of the MPO position with respect to Earth–bound radar station(s) (and then of Mercury center–of–mass around the Sun) The determination of the non–gravitational signals on the MPO by means of an on–board accelerometer The determination of the MPO absolute attitude by means of a Star– Tracker The determination of angular displacements of reference points on the solid surface of the planet, by means of a fotocamera 13 September 2007 8Iafolla et al. - ERE07

9. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario MORE: Science Goals Spherical harmonic coefficients of the gravity field of the planet up to degree and order 25 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 2 (C 20 and C 22 ) with 10 -9 accuracy (Signal/Noise Ratio 10 4 ) Degree 10 with SNR 300 Degree 10 with SNR 300 Degree 20 with SNR 10 Degree 20 with SNR 10 Love number k 2 with SNR 50 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) Obliquity of the planet to an accuracy of 4 arcsec (40 m on surface – needs also SYMBIO-SYS) Amplitude of physical librations in longitude to 4 arcsec (40 m on surface – needs SYMBIO-SYS). Amplitude of physical librations in longitude to 4 arcsec (40 m on surface – needs SYMBIO-SYS). C m /C (ratio between mantle and planet moment of inertia) to 0.05 or better C m /C (ratio between mantle and planet moment of inertia) to 0.05 or better C/MR 2 to 0.003 or better C/MR 2 to 0.003 or better 13 September 2007 9Iafolla et al. - ERE07

10. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario MORE: Science Goals Spacecraft position in a Mercury-centric frame to 10 cm – 1m (depending on the tracking geometry) Spacecraft position in a Mercury-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 107 (by combining MORE and BELA laser altimeter data ) Planetary figure, including mean radius, polar radius and equatorial radius to 1 part in 107 (by combining MORE and BELA laser altimeter data ) Geoid surface to 10 cm over spatial scales of 300 km Geoid surface to 10 cm over spatial scales of 300 km Position of Mercury in a solar system baricentric frame to better than 10 cm Position of Mercury in a solar system baricentric frame to better than 10 cm PN parameter, controlling the deflection of light and the time delay of ranging signals to 2.510 -6 PN parameter, controlling the deflection of light and the time delay of ranging signals to 2.510 -6 PN parameter, controlling the relativistic advance of Mercurys perihelion, to 510 -6 PN parameter, controlling the relativistic advance of Mercurys perihelion, to 510 -6 PN parameter (controlling the gravitational self-energy contribution to the gravitational mass to 210 -5 PN parameter (controlling the gravitational self-energy contribution to the gravitational mass to 210 -5 The gravitational oblateness of the Sun (J 2 ) to 210 -9 The gravitational oblateness of the Sun (J 2 ) to 210 -9 The time variation of the gravitational constant (d(lnG)/dt) to 310 -13 years -1 The time variation of the gravitational constant (d(lnG)/dt) to 310 -13 years -1 13 September 2007 10Iafolla et al. - ERE07

11. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario RSE total noise 13 September 2007 11Iafolla et al. - ERE07

12. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA accuracy requirement inside the frequency band 13 September 2007 12Iafolla et al. - ERE07

13. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario The ISA (Italian Spring Accelerometer) accelerometer developed at IFSI/INAF has been selected 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 310 –5 10 –1 Hz BepiColombo Radio Science Experiments ISA (Italian Spring Accelerometer) 13 September 2007 13Iafolla et al. - ERE07

14. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Direct solar radiation pressure: solar irradiance 13 September 2007 14Iafolla et al. - ERE07 http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant From http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant

15. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Direct solar radiation pressure: the transversal acceleration and its spectrum 13 September 2007 15Iafolla et al. - ERE07

16. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario mrmr K Al 5056 ISA mechanical oscillator and its equivalence with a linear harmonic oscillator: The accelerometer works at frequencies lower than the resonance frequency of the mechanical oscillator, where the transfer function between the acceleration of the sensitive mass and its displacement is: ISA General Description 13 September 2007 16Iafolla et al. - ERE07

17. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario The displacements of a proof–mass due to a perturbing acceleration are detected by means of capacitive transducers in a bridge configuration, followed by a low noise amplifier The capacitive bridge (CB) is biased at high frequency ( f p = 10 kHz ) so that accelerations at frequencies f s produce their unbalance At the output of the CB the signals are seen as a modulation of the bias voltage at the two side–bands f = f p f s in the frequency domain 2 f p ISA General Description 13 September 2007 17Iafolla et al. - ERE07

18. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Electromechanical actuator ISA calibration ISA General Description 13 September 2007 18Iafolla et al. - ERE07

19. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Solid tide of Earth Teleseismic (free oscillation of Earth) Seismic Noise Geophysical Measurements at the Istituto Nazionale di Fisica Nucleare (INFN) Gran Sasso Laboratory 13 September 2007 19Iafolla et al. - ERE07

20. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Differential Accelerometer: Mechanical Arrangement 08/06/2006 Emiliano Fiorenza 13 September 2007 20Iafolla et al. - ERE07

21. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Rejection: Electrical scheme 08/06/2006 Emiliano Fiorenza 13 September 2007 21Iafolla et al. - ERE07

22. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario 13 September 2007 Iafolla et al. - ERE0722 Pick Up System

23. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA experimental calibration: Seismic Noise Rejection 13 September 2007 23Iafolla et al. - ERE07

24. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Acceleration acting on ISA installed on a satellite The acceleration on a point P (ISA proof–mass) close to the MPO COM is: X Y Z ISA proof–mass Inside the MPO frame = Planet gravity = MPO angular rate = MPO angular acceleration = MPO–proof–mass vector Acceleration due to the planet gravity field gradients Centrifugal acceleration Angular acceleration Coriolis acceleration Non–Gravitational accelerations 13 September 2007 24Iafolla et al. - ERE07

25. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA mechanical configuration 13 September 2007 25Iafolla et al. - ERE07

26. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA mechanical configuration 13 September 2007 26Iafolla et al. - ERE07

27. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA Positioning This result suggest for the best configuration of the accelerometer a location with the three sensitive masses aligned along the rotation axis of the MPO, and with the com of the mass with sensitive axis along the rotation axis coincident with the com of the accelerometer as well as with the MPO one: Z–sensitive axis Y–sensitive axis X–sensitive axis com ISA COM Rotation axis 13 September 2007 27Iafolla et al. - ERE07

28. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario (XYZ) represents the MPO frame with origin in COM (xyz) defines the MPO position with respect to Mercury instantaneous orbital plane X–axis, along the radial direction (Mercury–MPO radius vector) Z–axis, along the out–of–plane direction (perpendicular to the orbital plane) Y–axis, along the transversal direction in the along–track direction ( ) ISA Positioning X Y Z ISA com COM Rotation axis YBYB Z B X B 13 September 2007 28Iafolla et al. - ERE07

29. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario com COM Requirements on ISA Positioning 13 September 2007 29Iafolla et al. - ERE07

30. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Case A: com COM 13 September 2007 30Iafolla et al. - ERE07 Requirements on ISA Positioning

31. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario Vibrational random noise on board the MPO inside the frequency band Micro-vibration random noise on board the MPO outside the frequency band 13 September 2007 31Iafolla et al. - ERE07 Vibrations

32. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA Block Diagram 13 September 2007 32Iafolla et al. - ERE07

33. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA OPERATIVE TEMPERATURE: -20/+30 [°C] ISA NON OPERATIVE TEMPERATURE: -40/+40 [°C] FEE ELECTRONIC STABILITY: 5*10^-8 [m/s^2/sqr(Hz)] ACC. MECHANICAL STABILITY:5*10^-7 [m/s^2/sqr(Hz)] Active thermal control Attenuation 700 ISA thermal system Over one orbital period (2.3 h) of the MPO Over one sideral period (44 days) of Mercury Random noise 4 °Cpp 25 °Cpp 4 °C/ Hz MPO Temperature Variations 13 September 2007 33Iafolla et al. - ERE07

34. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA thermal system overview QI=0.078W COVER_BOX BOTTOM_BO X PCB QI=0.88W OVEN_PCB THERMAL INSULATOR CONTROL ELECTRONIC SPACECRAFT GR=0,0005 GL=0,003 GL=0,5GR=0,014 GR=0,008 ENVIROMENT GR=0,0067 GL=0,3 GL=0,8 GL=0.03 GR=0,0028 GL=5 GR=0,05 GL=3 OVEN BOX ACCELEROMETER PAKAGES QI = 3.7 W ISA Thermal Mathematical model 13 September 2007 34Iafolla et al. - ERE07

35. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA Error Budget: Pseudo Sinusoidal Contributions 13 September 2007 35Iafolla et al. - ERE07

36. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA Error Budget: Random Contribution 13 September 2007 36Iafolla et al. - ERE07

37. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA Control Electronics ISA Detector Assy ISA PAYLOAD OVERVIEW 13 September 2007 37Iafolla et al. - ERE07

38. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA DETECTOR ASSY OVERVIEW Accelerometer Package 13 September 2007 38Iafolla et al. - ERE07

39. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario ISA Power and Mass Budget Overview * Without heaters 3,67 W ** After digital filtering, 80 kbps without filtering *** Whit margin 10% 13 September 2007 39Iafolla et al. - ERE07