Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST...

Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario

V. Iafolla1ST MORE TEAM MEETING

26-27 February 2007 RomeALCATEL ALENIA SPACE ITALIA

ISA (ITALIAN SPRING ACCELEROMETER): AN ACCELEROMETER TO MEASURE THE INERTIAL ACCELERATIONS

ACTING ON THE MPO.

Iafolla V. and the ISA Team

[email protected]




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

Task Name PI Valerio Iafolla Electrical Engineer Sergio Nozzoli Steering Committee Member David Lucchesi Steering Committee Member Giancarlo Bellucci Tracking Co-I Luciano Iess Gravitational effects evaluation. Vadim Milyukov Error budget evaluations Co-I Enrico Lorenzini Theoretical analysis Co-I Janusz B. Zielinski Electrical Engineer Responsible Luca Boschini System Engineering Manager Luca Soli Thermo-Mechanical Responsible Francesco Colombo PA Manager Marina Cesareo EGSE Responsible Marco Concolino Instrument Project Manager Maurizio Balasini SW Responsible Vania Vettorello MGSE Roberto Pavesi




Acceleration acting on ISA installed on a satellite

The acceleration on a point P (ISA proof–mass) close to the MPO COM is:

NGPARRRRgR 2

X

Y

Z

R

ISA proof–mass

Inside the MPO frame

= Planet gravity;

= MPO angular rate:

= MPO angular acceleration;

= MPO–proof–mass vector;

g

Acceleration due to the planet gravity field gradients

Centrifugal acceleration

Angular acceleration

Coriolis acceleration

Non–Gravitational accelerations

R




• Direct solar radiation pressure;

• Mercury albedo (indirect radiation pressure);

• Mercury infrared radiation;

The main NGPNGP acting on the MPO in Mercury’sMercury’s 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:

26101 sm28103 sm

Key rôle of ISA accelerometer


V. Iafolla




Mercury’s albedo radiation pressure

SunSunMerMerSunMerMer

Alb aaa

RA

cm

A

a

RAa

32

1

22

22

An order of magnitude estimate:

ĀMer 0.12 represents the average Bond albedo

RMer 2439 Km represents Mercury’sMercury’s equatorial radius

a 3389 km represents 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


V. Iafolla




R radial component;

T transversal component;

W out-of-plane component;

The GAUSS co-moving frame:

r

twwtr ˆˆˆ

wWtTrRA ˆˆˆ

Reference Frame


V. Iafolla




Solar Radiation: Radial acceleration

0 5000 10000 15000 20000 25000-1,5x10-6

-1,0x10-6

-5,0x10-7

0,0

5,0x10-7

1,0x10-6

Rad

ial a

ccel

erat

ion

(m/s

2 )

Time (seconds)

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 108 m/s2

1 Orbital period

½ Orbital period

1/3 Orbital period

108 m/s2

100

No modelling of the solar radiation




0 5000 10000 15000 20000 25000-1,5x10-6

-1,0x10-6

-5,0x10-7

0,0

5,0x10-7

1,0x10-6

1,5x10-6

Tran

sver

sal a

ccel

erat

ion

(m/s

2 )

Time (seconds)

The perturbing effect at the orbital period (2.3 h) is about

2 orders–of–magnitude larger than the

accelerometer accuracy of 108 m/s2

3 orbital periods 7 hours… the most important in the MPO

orbit reconstruction …

108 m/s2

100

No modelling of the solar radiation

Solar Radiation: Transversal acceleration




0 5000 10000 15000 20000 25000

0

1x10-8

2x10-8

3x10-8

4x10-8

5x10-8

Rad

ial a

ccel

erat

ion

(m/s

2 )

Time (seconds)

108 m/s2

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

108 m/s2

1 Orbital period

No modelling of the albedo radiation

Albedo: Radial acceleration




0 5000 10000 15000 20000 25000

-4,0x10-9

-2,0x10-9

0,0

2,0x10-9

4,0x10-9

Tran

sver

sal a

ccel

erat

ion

(m/s

2 )

Time (seconds)

108 m/s2

The perturbing effect at the orbital period (2.3 h) is

smaller than the accelerometer accuracy of

108 m/s2

No modelling of the albedo radiation

Albedo: Transversal acceleration




RSE total noise




ISA accuracy requirement inside the frequency band

Frequency Hz 5103 34 1010 110

Acceleration values Hzsm // 2 8103 810 710




mr

K

HzI

kf t 5.3

2

10

Al 5056

ISA mechanical oscillator and its equivalence with a linear harmonic oscillator:

MkI tt Fkxxxmr

Hzm

kf

r

5.32

10

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:

20 a

x

ISA General Description




• 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 ( fp = 10 kHz ) so that

accelerations at frequencies fs 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 = fp fs in the frequency domain;

2fp





ISA Electrical and mechanical Parameters

mina ISA total intrinsic noise Hzsm // 2 1010*1.4 2

bwa Brownian noise Hzm /)sec/( 22 2010*16 2

ela Electronic noise Hzm /)sec/( 22 2110*5.1

rm Proof mass (Kg) 0.22 of Frequency of resonance (Hz) 3.5

pf Polarisation frequency (KHz) 10 P Pressure condition ( mbar ) 32 1010

1C Sensing capacity (pF) 300 1Ctg Loss of 1C 410*4

aC External fixed capacity (pF) 300

Catg Loss of aC 410*3 Electronic device AD743/AD

nv Voltage noise of amplifier ( HzV / ) 910*3

ni Current noise of amplifier ( HzA / ) 1510*7

nT Temperature noise of amplifier (K) 0.76 Transducer factor ( mV / ) 510 Electromechanical transducer factor 210*3

deQ Electric quality factor 410*3.5

mQ Mechanical quality factor 10 Q Total quality factor 10




Electromechanical actuatorSuperimposing an alternate voltage )2cos(0 tfvv e

to the constant voltage V

vVb

d

CM

20

01

ef

2

02 2

vd

CbM

ef2

ISA calibration





12.74 12.75 12.76 12.77 12.78 12.79 12.8

-8.246

-8.244

-8.242

-8.24

-8.238

-8.236

x 10-3

Ac

ce

lera

zio

ne

[g

]

Tempo giorni dal 2001

Misure GEOSTAR

Earthquakes 13 gen 2001 17:33:29:22Off Coast of Central AmericaRegistrazione Gravimetro Geostar Ustica

Solid tide of Earth

Teleseismic (free oscillation of Earth)Seismic Noise

Geophysical Measurements at theIstituto Nazionale di Fisica Nucleare (INFN) Gran Sasso Laboratory




Differential Accelerometer: Mechanical ArrangementDifferential Accelerometer: Mechanical Arrangement

08/06/2006 Emiliano Fiorenza




Pick Up Pick Up SystemSystem





Rejection: Electrical scheme Rejection: Electrical scheme





Seismic Noise RejectionSeismic Noise Rejection




Vibrational random noise on board the MPO inside the frequency band

Frequency Hz 5103 34 1010 110

Acceleration values ( Hzsm // 2 ) 9103 910 810

Micro-vibration random noise on board the MPO outside the frequency band




ISA Block Diagram

Hzf 5.30

10Q 610

Dynamic

decdB

Hzf

FiltericAna

cat

/40

1

log

65536

Dynamic

HzatdB

Hzf

FilterDigital

cat

180

1.0

ISA Microvibration noise




(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 ( );ZYX ˆˆˆ

ISA Positioning

X

Y

Z

R

ISA com

COM

Rotation axis

YB

Z B

X B

0R

tR

)()(00 tRtRRRR tt

ISA Gauss frame

X Y Z

ISA LVLH frame

ZLVLH XLVLH YLVLH




ISA PositioningThis 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

comISA COM

Rotation axis

000

10500

105002

2

000

000

000

0

0

0

ZYX

ZYX

ZYX

Z

Y

X

ZZZ

YYY

XXX

R

R

R




ISA mechanical configuration




ISA PositioningAngular rate and angular acceleration

Z

Y

X

0

Z

Y

X

0

The angular rate and acceleration along the MPO axes are:

where and are the nominal values:0 0

where M represents the MPO mean anomaly around Mercury, and e 0.162 the MPO eccentricity;

32

0 2cos2

5cos21 eOMeMen

3220 2sin5sin2 eOMeMen

nM

f

f = true anomaly

Satellite mean motion




z

yX

yY

xY

xX

ZISA

ZMeMee

Zn

ZMeMen

Zn

ZMeMen

na

2cos2

9cos3

2

31

2cos2

5cos21

2cos2

5cos21

22

22

22

2

zX

zY

yZ

y

xZ

x

YISA

Yn

YMeMen

YMeMen

YMeeMe

Yn

YMeMe

na

22

222

22

2

2cos2

5cos21

2cos2

5cos2122cos

2

5

2

1cos

2sin5sin2

zY

zX

yZ

y

xZ

x

XISA

Xn

XMeMen

Xn

XMeMe

XMeMen

XMeeMe

na

22

22

222

2

2cos2

5cos21

2sin5sin2

2cos5cos422cos165cos103

Solution for the gravitational (tide) and apparent accelerations: general case




ISA PositioningIn 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:

2890 /1010 smgA

Position ranges Position accuracies

0X 0 0X ±4 mm

tX ±30 mm ±30 mm

tX ±1 mm ±5 mm

0Y 0 0Y ±5.5 mm

tY ±20 mm ±20 mm

tY ±2 mm ±7.5 mm

0Z 0 0Z ±11 mm

tZ ±40 mm ±40 mm

tZ ±4 mm ±15 mm

)()(00 tRtRRRR tt




Requirements on the angular rate and angular acceleration for the following fixed values of the position of the spacecraft COM: Xt = 30 mm, Yt = 20 mm and Zt = 40 mm.

Case A) Case B) Hzsrad51034.1 Hzsrad51054.0 Hzsrad 281076.1 Hzsrad 281056.0

Case A: com ≡ COM

Case B: com +20 cm ≡ COM




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:

Cg /105 8

278 105105 smg

±2 °C

±12.5 °C 4 °C/Hz




ISA thermal system overview

QI=0.078W

COVER_BOX

BOTTOM_BOX

PCB QI=0.88WOVEN_PCB

THERMAL INSULATOR

CONTROL ELECTRONIC

SPACECRAFT

GR=0,0005

GL=0,003

GL=0,5 GR=0,014

GR=0,008

ENVIROMENT

GR=0,0067

GL=0,3

GL=0,8

GL=0.03

GR=0,0028

GL=5

GR=0,05GL=3

OVEN BOX

ACCELEROMETERPAKAGES

QI = 3.7 W

ISA Thermal Mathematical model




ISA Error Budget: Pseudo Sinusoidal Contributions

Type Due to Spectral content

requirement on

Error % A0

Gravity-gradients

n Orbital period P and ½P

Apparent forces 00 ;

Orbital period P and ½P

0R ; tRt

85%A0

Thermal effects

2 °C Orbital period P and ½P

T 15%A0

Components coupling

Misalignment angle

Orbital period P and ½P Negligible

Total 100%A0

"ISA accelerometer onboard the Mercury Planetary Orbiter: error budget“ Celestial Mech Dyn Astr DOI 10.1007/s10569-006-9059-0http://dx.doi.org/10.1007/s10569-006-9059-0




ISA Error Budget: Random Contributions

Type Due to Spectral content requirement

on

Error

percent

Apparent forces tRR t

;0 Random ; 60%A0

Thermal effects HzC4 Random T 30%A0

Noise on the MPO Movements due to the

HGA, fuel sloshing ecc. Random 10%A0

MPO COM

displacement

Movements due to the

HGA and fuel

consumption ecc.

Random tRt

70%A0

Components

coupling Misalignment angle Random Negligible

ISA intrinsic noise Random Negligible

Total (not correlated noise) <100%A0




ISA Control Electronics

ISA Detector Assy

ISA PAYLOAD OVERVIEW




ISA Detector Assy

External Shield

Internal Thermal shieldAccelerometer ThermalInsulation

Electrical I/F

ISA DETECTOR ASSY OVERVIEW

Accelerometer Package




ISA Simulator (simulink)

Mechanical Signal

Mechanical noise

ISA Mechanical

system

Output

Thermal noise

ISA simulator diagram

ISA Thermalsystem

Input signal Electro-mechanical system

Mechanical oscillator Thermal system with active control




ISA Signal and noise in the radial direction

ISA displacement:[4cm+/-5mm; 4cm+/-7mm; 20cm+/-15mm]




Integration




Name / acronym Italian Spring Accelerometer / ISA

Objectives To measure the inertial acceleration acting on the MPO with high precision. The scientific objectives are connected with those of the RadioScience Experiment, i.e., a set of experiments that can give information on the Mercury structure and to test Einstein’s theory of General Relativity.

General description

Three axes accelerometer with masses mechanically suspended by a spring and with a capacitive transducer.

Parameter

Units

Value/Description

Remarks

Reference P/L N/A ISA-Italian Spring Accelerometer

Developed to the IFSI

Proof Mass Suspension N/A Mechanical Transducer N/A Capacitive

Mechanical Parameter Proof masses Kg 0.22 Resonace frequency Hz 3.5 Mechanical quality factor // 10 Length of arms m 31045

Electrical Parameters Detection capacitors. pF 300 Electrical loss in the detectors capacitors

410*4

External fixed capacitors pF 300 Equivalent voltage noise generator.

HzV /

910*3

Equivalent current noise generator.

HzA /

1510*7

Amplifier temperature noise °K 0.38 Transducer factor V/m 510

Electromechanical Transducer factor

210*3

ORBIT Inclination . Type of orbit N/A Circular preferred,

elliptic acceptable

Altitude km No requirement Pericenter precession No requirement Periapsis longitude change °/orbit No requirement Phase angle No requirement




CONFIGURATION Units # Layout N/A Preferred location N/A COM

Thermal stabilized

area

The location wrt the MPO COM is related to the knowledge of the rotation state of the MPO. The accuracy in the knowledge of the position of the proof masses must be 5mm in the zenith direction, 7mm along track and 15mm in the out of plane direction.

PHYSICAL According to configuration layout Mass, total kg 5.5 Baseline with active thermal control Mass, mechanical part kg 4 Mass, electronics kg 1.5 Mass, harness kg 0.15+0.4/m Dimension (mechanics) mm 300 x 170x180 Baseline with active thermal control Dimension (electronics) mm 170x130x70 Baseline with active thermal control

POWER According to operational modes Electronic power dissipation W 5.2 Without heather Total Average power dissipation W 7.07 Nominal power, with heather and in worst case condition Total Peak power dissipation W 8.9 Peak power, with heather and in worst case condition

DATA RATE/VOLUME Data volume Gbit 94.6 2 years Data volume/orbit (nominal) Gbit 0.0125 Data rate (nominal) Kbit/s 1.5 Filtered data Data rate (burst) Kbit/s 80 For TBD time

POINTING Pointing control APE arcsec 69 Attitude reconstruction AME arcsec 69 Pointing stability RPE arcsec

/8hours 69

Alignment knowledge respect to the MPO LVLH frame

mrad 0.3 This value is determinate to the ISA dynamic

Alignment stability mrad Better than 0.3 Co-Alignment w.r.t. other P/L mrad Better than 0.3 Co-Alignment Stability mrad Better than 0.3

THERMAL Detector Assy C -20;+45 TBC Operative range Detector Assy C -30;+55 TBC Non Operative range Detector Assy I/F Orbital stability

C/orbit +/-2

Detector Assy I/F sideral stability

C/Mercury year

+/-12.5

Electronic unit °C -20;+45 TBC Operative range Mechanical stability vs temperature Hzsm // 2

7105

Electronics stability vs temperature Hzsm // 2

8105




ReferencesBertotti, 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);

Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST...

Documents

Transcript of Istituto Nazionale Di AstrofisicaIstituto di Fisica dello Spazio Interplanetario V. Iafolla 1 ST...