1. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA (ITALIAN SPRING ACCELEROMETER): AN ACCELEROMETER TO MEASURE THE INERTIAL ACCELERATIONS ACTING ON THE MPO. Iafolla V. and the ISA Team Valerio.iafolla@ifsi-roma.inaf.it

2. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA team IFSI (Istituto di Fisica dello Spazio Interplanetario), INAF, Rome Italy AAS_I Harvard-Smithsonian Center for Astrophysics Cambridge MA, USA Sternberg Astronomical Institute, University of Moscow Russia Space Research Centre, Warsaw Poland

3. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA 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

4. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Precise Orbit Determination and RSE Accuracy in the along-track orbit reconstruction. of about 1 m over one orbital revolution of the MPO around Mercury, i.e., over 8355 s. The requested accuracy corresponds to an along-track acceleration of about 10 8 m/s 2. This quantity has been assumed equal to ISA measurement error over the arc length during the POD. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla

5. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Direct solar radiation pressure; Mercury albedo (indirect radiation pressure); Mercury infrared radiation; NGPMercurys The main NGP acting on the MPO in Mercurys thermal environment are: The more important in terms of the magnitude of the disturbing acceleration on the MPO orbit are: 1.the solar radiation acceleration: 2.Mercury albedo acceleration: Key rôle of ISA accelerometer Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla

6. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA MPO In the following numerical analyses the MPO has been assumed spherical in shape with approximately the same area–to–mass ratio of the planned spacecraft: MPO A/m 1.9 10 2 m 2 /kgcorresponding to an MPO mass 357 kg where c represents the speed of light and Ŝ the unit– vector toward the Sun. The radiation coefficient has been assumed 1, i.e., neglecting the diffusive term of the reflected radiation. The penumbra effects have been considered because of the vicinity of the Sun. Direct solar radiation pressure Key rôle of ISA accelerometer Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla

7. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Mercurys albedo radiation pressure An order of magnitude estimate: Ā Mer 0.12 represents the average Bond albedo Mercurys R Mer 2439 Kmrepresents Mercurys equatorial radius a 3389 kmrepresents the MPO semi–major axis In a simplified approach the albedo acceleration has a component along both the radial and solar direction. Key rôle of ISA accelerometer Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla

8. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA R radial component; T transversal component; W out-of-plane component; The GAUSS co-moving frame: Reference Frame Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla

9. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Solar Radiation: Radial acceleration 3 orbital periods 7 hours The perturbing effect at the orbital period (2.3 h) is about 2 orders–of–magnitude larger than the accelerometer accuracy of 10 8 m/s 2 1 Orbital period ½ Orbital period 1/3 Orbital period 10 8 m/s 2 100 No modelling of the solar radiation

10. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA The perturbing effect at the orbital period (2.3 h) is about 2 orders–of–magnitude larger than the accelerometer accuracy of 10 8 m/s 2 3 orbital periods 7 hours … the most important in the MPO orbit reconstruction … 10 8 m/s 2 100 No modelling of the solar radiation Solar Radiation: Transversal acceleration

11. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA 10 8 m/s 2 2 ? 3 orbital periods 7 hours The perturbing effect at the orbital period (2.3 h) is only a factor 2 larger than the accelerometer accuracy of 10 8 m/s 2 1 Orbital period No modelling of the albedo radiation Albedo : Radial acceleration

12. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA 10 8 m/s 2 The perturbing effect at the orbital period (2.3 h) is smaller than the accelerometer accuracy of 10 8 m/s 2 No modelling of the albedo radiation Albedo: Transversal acceleration

13. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA RSE total noise

14. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA accuracy requirement inside the frequency band

15. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA 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

16. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA 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

17. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Electrical and mechanical Parameters

18. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Electromechanical actuator Superimposing an alternate voltage to the constant voltage V ISA calibration ISA General Description

19. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Solid tide of Earth Teleseismic (free oscillation of Earth)Seismic Noise Geophysical Measurements at the Istituto Nazionale di Fisica Nucleare (INFN) Gran Sasso Laboratory

20. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Differential Accelerometer: Mechanical Arrangement 08/06/2006 Emiliano Fiorenza

21. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Pick Up System 08/06/2006 Emiliano Fiorenza

22. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Rejection: Electrical scheme 08/06/2006 Emiliano Fiorenza

23. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Seismic Noise Rejection

24. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Vibrational random noise on board the MPO inside the frequency band Micro-vibration random noise on board the MPO outside the frequency band

25. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Block Diagram ISA Microvibration noise

26. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA (XYZ) represents the MPO frame with origin in COM; (xyz) define 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

27. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA 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

28. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA mechanical configuration

29. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Positioning Angular rate and angular acceleration The angular rate and acceleration along the MPO axes are: where and are the nominal values: where M represents the MPO mean anomaly around Mercury, and e 0.162 the MPO eccentricity; f = true anomaly Satellite mean motion

30. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Solution for the gravitational (tide) and apparent accelerations: general case

31. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Positioning In order to determine the constraints in the possible displacements along the three sensitive axes, we need to compare the previous formula with the accelerometer accuracy:

32. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Case A: com COM Case B: com +20 cm COM

33. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA 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; over one sidereal period (44 days) of Mercury; Random noise; In the actual version of the ISA accelerometer the thermal stability is: That is a temperature change of 1 degree produces a voltage output equivalent to: ±2 °C ±12.5 °C 4 °C/ Hz

34. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA 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

35. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Error Budget: Pseudo Sinusoidal Contributions "ISA accelerometer onboard the Mercury Planetary Orbiter: error budget Celestial Mech Dyn Astr DOI 10.1007/s10569-006-9059-0 http://dx.doi.org/10.1007/s10569-006-9059-0

36. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Error Budget: Random Contributions

37. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Control Electronics ISA Detector Assy ISA PAYLOAD OVERVIEW

38. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA DETECTOR ASSY OVERVIEW Accelerometer Package

39. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Simulator (simulink) Mechanical Signal Mechanical noise ISA Mechanical system Output Thermal noise ISA simulator diagram ISA Thermal system Input signalElectro-mechanical system Mechanical oscillator Thermal system with active control

40. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA ISA Signal and noise in the radial direction ISA displacement: [4cm+/-5mm; 4cm+/-7mm; 20cm+/-15mm]

41. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA Integration

42. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA

43. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA

44. Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST MORE TEAM MEETING 26-27 February 2007 Rome ALCATEL ALENIA SPACE ITALIA References Bertotti, B., Iess, L., Tortora, P., A test of general relativity using radio links with the Cassini spacecraft, Lett. to Nature 425, 2003; Fuligni, F., Iafolla, V., 1997. Measurement of small forces in the physics of gravitation and geophysics. Il Nuovo Cimento 20 C (5), 637–642; Fuligni, F., Iafolla, V., Milyukov, V., Nozzoli, S., 1997. Experimental gravitation and geophysics. Il Nuovo Cimento 20 C (5), 637–642; Iafolla, V., Nozzoli, S., Mandiello, A., 1998. High sensitive accelerometer for fundamental physics in space. Second Joint Meeting of the International Gravity Commission and the International Geoid Commission, Trieste, 7–12, September; Iafolla, V., Nozzoli, S., 2001. Italian spring accelerometer (ISA) a high sensitive accelerometer for BepiColombo ESA CORNERSTONE. Plan. Space Science, 49, 1609–1617; Iafolla, V., Lucchesi, D.M., Nozzoli, S., 2004. On the ISA accelerometer positioning inside the Mercury Planetary Orbiter. Plan. and Space Scien., in press. Milani, A, Vokrouhlicky, D., Villani, D., Bonanno, C., Rossi, A., Testing general relativity with the Bepicolombo radio science experiment, Phs. Rev. D 66, 2002; Milani A, Rossi, A., Villani, D., The BepiColombo Radio Science Simulations, Version 2, 11 April (2003);