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July 21, 2002-4th LISA Symposium S. Vitale 1
The LISA Technology Package on-board
SMART-2 and the test of free fall for LISAS. Vitale
Department of Physics, University of Trento, and INFN, Trento, Italy
July 21, 2002-4th LISA Symposium S. Vitale 2
ΛΤΠ
And the LISA Technology Package Architect Team
ESTEC Contract #15580/01/NL/HB
July 21, 2002-4th LISA Symposium S. Vitale 3
Detecting curvature by geodesic deviation
Difference of acceleration for
particle located at different places
xδ
metric2
ij j2
d h1 x2 dt
≈ δ
2 i2 i j
0 j02curvature
d x c R xdtδ = δ GW
July 21, 2002-4th LISA Symposium S. Vitale 4
2 22
1 hL
x LFm
∆ω + ωω
=δ2 22
1 hL
x LFm
∆ω + ωω
=δ
2
2
2
2F dd x
dth L
dtm+∆=δ
LISA sensitivity and the importance of free-fall
“Curvature”noise
Fourier2 2
21 h
Lx LF
m∆ω + ω
ω=δ
Parasitic forces Test-mass Separation
July 21, 2002-4th LISA Symposium S. Vitale 5
Importance of low frequency, an example:
LISA calibration binaries
July 21, 2002-4th LISA Symposium S. Vitale 6
LISA
( )12
215
a 2
f m 1S f 3 10 13 mHz s Hz
− ≤ × +
0.1 mHz f 30 mHz≤ ≤
July 21, 2002-4th LISA Symposium S. Vitale 7
5 106 km
SMART-2 In-flight test:
squeezing 1 LISA’sarm to 35 cm
214 msa 3 10 1 mHz f 30 mHz
Hz
−−δ ≤ ⋅ ≤ ≤
July 21, 2002-4th LISA Symposium S. Vitale 8
Test-masses(gravitational sensor) Interferometer
The LISA technology package (LTP)
July 21, 2002-4th LISA Symposium S. Vitale 9
Spacecraft
Test massx
Displacement sensor
Thrusters
High gain force feedback
Keeping the spacecraft with the proof-mass
July 21, 2002-4th LISA Symposium S. Vitale 10
Goal of the measurement:
LISA acceleration noise
Force on spacecraft
S C2T / Mp n 2
fbSensor noiseParasitic stiffnessForce on Test-Mass Drag free
gain
Relative diplacementTM wrt
nois
/
e
S C
Ff xm M
a
−
+ ω + ω
=
Force on spacecraft
S C2p n 2
fbSensor noiseParasitic stiffnessDrag free
gain
Relative diplacementTM wrt
T / Mnoise
Force on Test-Mass
S/C
Fx
Mfam
−
+ ω + ω
=
Force on spacecraft
2T / Mnoise p
Parasitic stiffnessForce on Test-Mass
Relative diplacementTM wrt
S Cn 2
fbSensor noiseDrag free
ga
S
in
/C
Fx
Mfam
−
= + ω ω
+
Force on spacecraft
2T / Mnoise p n
Sensor noiseParasitic stiffnessForce on Test-Mass
Relative diplacementTM wrt
S C2fb
Drag freegain
S/C
FM
fa xm
−
= + ω
+ω
Force on spacecraft
S C2T / Mnoise p n 2
fbSensor noiseParasitic stiffnessForce on Test-Mass Drag free
gain
Relative diplacementTM wrt S/C
Ffa xm M
−
= + ω + ω
July 21, 2002-4th LISA Symposium S. Vitale 11
Purpose of the in-flight test
• Demonstrate ( )12
214
a 2
f m 1S f 3 10 13 mHz s Hz
− ≤ × +
for 1 mHz f 30 mHz≤ ≤
• Independent measurement of the thrust noise level 2S C fbF Mω .
• Independent measurement of intrinsic fluctuating forces intf m
• Measurement of the stray stiffness 2pω of coupling between the test-mass and the spacecraft.
• Measurement of intrinsic sensor cross-talk and thrusters misalignments • Test of the low frequency suspension. • Test of the charge management procedures • Test of laser beam alignment via rotation of the test-mass • Test of the S/C attitude control scheme that uses the test-masses as a reference, as in the initial
beam acquisition scheme of LISA. • Test of the two-masses/two-axes control loop as in LISA. • Sensitivity to magnetic fields • Sensitivity to power fluctuations • Sensitivity to thermal gradients • Sensitivity to gravitational noise • Sensitivity to working point
July 21, 2002-4th LISA Symposium S. Vitale 12
x
y
z
φ
η
θ
TM1
TM2
Basic output:
TM distance as read by the laser interferometer
July 21, 2002-4th LISA Symposium S. Vitale 13
The basic mode of operation
July 21, 2002-4th LISA Symposium S. Vitale 14
( ) [
( ) ( )
( )
2 2 2 2 2 2lfs p2 n,laser lfs p2 n2 lfs
ActuationLaser Noise Baseline distortion noise
2 2lf
laser 2 2 2lfs p2
Stiffness ofsuspended TM
2 S / Cp12 n1 2
fbs p
1x
x
Fx
x x
M
ω + ω − ω + δ ω + ω + ω −
−
δ ≈ ×ω − ω + ω
ω + ω −
ω + ω
n
T M1
a
T M2
mf
mf
+
−
July 21, 2002-4th LISA Symposium S. Vitale 15
( ) [
( ) ( )
( )
2
laser 2 2 2lfs p2
Stiffness ofsuspended TM
2 2 2lfs p2 n,l
2 2lfs p2 n2 lfs
ActuationBaseline distortion n
aser
Laser Noise
2 S / Cp1 n1 2
f
oise
2 2lf
bs p2
1x
x
FxM
x x
δ ≈ ×ω − ω + ω
+ δ ω + ω + ω −
− ω + ω
ω + ω − ω
ω + ω
−
n
T M1
a
T M2
mf
mf
+
−
July 21, 2002-4th LISA Symposium S. Vitale 16
( ) [
( ) ( )
( )
laser 2 2 2lfs p2
Stiffness ofsuspended TM
2 2 2 2 2lfs p2 n,laser lfs p2
Laser Noise Baseline distor
2n2 lfs
Actuationnoise
2 2lfs p2
tion
2 S / Cp1 n1 2
fb
1x
x
FxM
xx
δ
+ ω −
−
≈ ×ω − ω + ω
ω + ω − ω + δ ω + ω
ω + ω
ω + ω
−
n
T M1
a
T M2
mf
mf
+
−
Thermalstability
July 21, 2002-4th LISA Symposium S. Vitale 17
( ) [
( ) ( )
( )
laser 2 2 2lfs p2
Stiffness ofsuspended TM
2 2 2 2 2 2lfs p2 n,laser lfs p2 n2 lfs
ActuationLaser Noise Baseline distortion noise
2 2lfs
2 S / Cp1 n1 2
b2
fp
1x
x x x
FxM
δ ≈ ×ω − ω + ω
ω + ω − ω + δ ω + ω + ω −
ω + ω
− ω + ω − n
T M1
a
T M2
mf
mf
+
−Use Laser
July 21, 2002-4th LISA Symposium S. Vitale 18
( ) [
( ) ( )
( )
laser 2 2 2lfs p2
Stiffness ofsuspended TM
2 2 2 2 2 2lfs p2 n,laser lfs p2 n2 lfs
ActuationLaser Noise Baseline distortion noise
2 2lfs
2 S / Cp1 n1 2
b2
fp
1x
x x x
FxM
δ ≈ ×ω − ω + ω
ω + ω − ω + δ ω + ω + ω −
ω + ω
− ω + ω − n
T M1
a
T M2
mf
mf
+
−
( ) [
( ) ( )
( )
laser 2 2 2lfs p2
Stiffness ofsuspended TM
2 2 2 2 2 2lfs p2 n,laser lfs p2 n2 lfs
ActuationLaser Noise Baseline distortion noise
2 2lfs
2 S / Cp1 n1 2
b2
fp
1x
x x x
FxM
δ ≈ ×ω − ω + ω
ω + ω − ω + δ ω + ω + ω −
ω + ω
− ω + ω − n
T M1 T M2
a
f fm m
+ −
Intrinsically a gradiometer
July 21, 2002-4th LISA Symposium S. Vitale 19
2 2 2lfs p2 p12 0 ω ≈ −ω ≈ −ω ≥
( ) [
( ) ( )
( )
laser 2 2 2lfs p2
Stiffness ofsuspended TM
2 2 2 2 2 2lfs p2 n,laser lfs p2 n2 lfs
ActuationLaser Noise Baseline distortion noise
2 2 2 S / Clfs p2 p1 n1 2
fb
1x
x x x
FxM
δ ≈ ×ω − ω + ω
ω + ω − ω + δ ω + ω + ω −
− ω + ω − ω + ωn
T M1 T M2
a
f fm m
+ −
( )2 -2
pω s
(Hz)
Fig. 1. Open loop gain (red line) and overall coupling stiffness (yellow line) for one possible controllaw for the low frequency electrostatic suspension.
2 2 2 2lfs p2 p1 p1 2ω + ω − ω ≈ ω
July 21, 2002-4th LISA Symposium S. Vitale 20
July 21, 2002-4th LISA Symposium S. Vitale 21
ID Action
14 Main loop 15 Control to science mode16 Transfer from accelerometer mode to low freq. Suspe17 Attitude to hybrid mode18 Discharge19 Charge measurement20 Discharge21 Transitory decay22 Final laser beam alignment23 Measurement phase24 M1 basic measurement25 M1 double-check26 Interchange 1 and 227 Transitory decay28 Measurement29 Transfer to Accelerometer Mode
Main loop 21 h5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
2 3
July 21, 2002-4th LISA Symposium S. Vitale 22
( ) ( ) ( ) S / C,x2 2 2 2xlaser p2 n,laser p2 p1 n,1 22 2 2
fb,xlfs2 p2
F1 fx x xm M
∆δ ≈ ω − ω + + ω − ω + ωω + ω − ω
Locking onto the laser output
July 21, 2002-4th LISA Symposium S. Vitale 23
Stiffness measurement, adding a signal in the drag-free control loop
x
July 21, 2002-4th LISA Symposium S. Vitale 24
x
July 21, 2002-4th LISA Symposium S. Vitale 25
x
July 21, 2002-4th LISA Symposium S. Vitale 26
x
July 21, 2002-4th LISA Symposium S. Vitale 27
2p1
laser cal2
2x x
ωδ ≈
ω
July 21, 2002-4th LISA Symposium S. Vitale 28
July 21, 2002-4th LISA Symposium S. Vitale 29
July 21, 2002-4th LISA Symposium S. Vitale 30
3× +
July 21, 2002-4th LISA Symposium S. Vitale 31
Θ
xLTP
xDRS
h DRS-LTP an enhanced testopportunity
July 21, 2002-4th LISA Symposium S. Vitale 32
Table 1 Summary of LTP-DRS accommodation trade-off
Θ(°) 2-axes 2-masses control with separate packages
Correlation analysis between packages
Redundancy for loss of 1 IS
Gravitational calibration maximum
SNR 0 No Full Yes 215
30 Marginal Yes Yes 165 45 Yes Yes Yes 135
60 Closest to LISA Configuration Yes Yes 138
90 Yes No No 121
July 21, 2002-4th LISA Symposium S. Vitale 33
Table 1. Amplitude of achievable calibration signals with 100 µm displacement of TM
Θ(°)
LTP test-masses difference of acceleration
( fms-2) for 100 µm displacement of DRS TM
along xDRS
LTP test-masses difference of acceleration
( fms-2) for 100 µm displacement of DRS TM
along yDRS
LTP test-masses difference of acceleration
( fms-2) for 100 µm displacement of DRS TM
along zDRS 0 249 0 125 30 170 130 161 45 82 172 193 60 14 155 220 90 114 57 242
July 21, 2002-4th LISA Symposium S. Vitale 34
Requirements
July 21, 2002-4th LISA Symposium S. Vitale 35
( )12
214
a 2
f m 1S f 3 10 13 mHz s Hz
− ≤ × +
1 mHz f 30 mHz≤ ≤
July 21, 2002-4th LISA Symposium S. Vitale 36
S/C and external disturbance
Apportioning
LTP
Inertial Sensor
Table 1. Allocated contributions to the overall noise budget for LISA and SMART-2
SMART-2
( )3 210 f Hz 3 10− −≤ ≤ × LISA
( )4 110 f Hz 10− −≤ ≤ Source IS
2intp n
IS sources
f xm
+ ωOut
S C2intp 2
fb
Extrernal sources
Ffm M
+ ωω
IS2intp n
IS sources
f xm
+ ωOut
S C2intp 2
fb
Extrernal sources
Ffm M
+ ωω
21
LTP S/C
Allocated contribution 2 2
15 f ms10 13 mHz Hz
−−
× +
21
15 15
2.1 2.1
July 21, 2002-4th LISA Symposium S. Vitale 37
Apportioning complicated by non-linearity
( )
( )
noise
IS sources
LTP
S / C+Extern
LT
2 2 2pIS pLTP pS / C n
S C2 2 2pIS pL
al source
S /
PT /
TP
s
IST /
pS /
M
CT / M
C
M
2fb
a
fm
fm
f x
FM
m=
+
+
+ ω + ω + ω
+ ω + ω + ωω
( )
( )
noise
IS sources
LTP
S / C+Extern
LT
2 2 2pIS pLTP pS / C
2 2 2pIS pL
S / CS CT
I
/TP pS /
al sources
S
M
T
PT / M
C
/ Mn
2fb
a
fm
Ffm
f x
M
m=
+
+
+ ω + ω + ω
+ ω + ω + ωω
( )
( )
noise
IS sources
LTP
S / C+Externa
2pLTP
LTP
IS2T / M 2
pS / C
S / CS C2T
l source
/ MpS / C
pIS n
2pI 2
fbS
T / M
2pLTP
s
Ffm
f
ma
M
x
m
f= + + +
+
+
ω
ω +ω+ω
+ ω
ω ω
Independent requirement needed for stiffness
July 21, 2002-4th LISA Symposium S. Vitale 38
22 7 2p
f4 10 1 s3 mHz
− − ω ≤ × +
LISA
( )22 15 2p S/ Cx 1 10 1 f 3mHz m s− − ω ≤ × +
SMART-2
5×
2×10×
July 21, 2002-4th LISA Symposium S. Vitale 39
Table 1. Top level requirement for stiffness along the sensitive axes.
SMART-2
( )3 210 f Hz 310− −≤ ≤ LISA
( )4 110 f Hz 10− −≤ ≤ Source
External sources IS sources External sources IS sources
LTP S/C Allocated contribution 2
7 2f10 1 s3mHz
− − × +
5 5 10 1 3
Extra stiffness due to actuation
2 Maximum ForceStiffnesseffective gap
×≈
July 21, 2002-4th LISA Symposium S. Vitale 40
Cross-talk
2x,cross talk x,
S / C wrt T/Mcoupling motion along stiffness
f − = ω × ∆#
#
#
•Actuation: force applied along wrong DOF
•Sensing: sensor detects motion along wrong DOF
•Dynamical: parasitic springs have off-diagonal terms
July 21, 2002-4th LISA Symposium S. Vitale 41
Table 1 Drag-free and attitude control requirements and displacement noise allocation in M1
Units Frequency range
Attitude 910 rad Hz−×
Displacement ×10-9 m/√Hz ( )3 210 f Hz 310− −≤ ≤
2 2S C fb ,x S C fb ,xF M , Iω Γ ω Total control
level Ref. Num DOF
xn /θn
ψ =0.01 (≈0.6°) ψ =0.1 (≈6°) ψ =0.01 (≈0.6°)
ψ =0.1 (≈6°)
1 xS/C 1.8 4.7 5 5 2 No
measurement on y
1.8 47 4.7 50 5
3
y2,S/C
Measurement on y 1.8 4.7 5 5
4 No measurement
on y 1.8 66 6.6 69 6.9
5
y1,S/C
Measurement on y 1.8 6.6 6.6 9.5 9.5
6 z1S/C 18 47 4.7 50 19 7 z2S/C 18 66 6.6 69 19 8 θ1S/C 65 235 23.5 243 68
July 21, 2002-4th LISA Symposium S. Vitale 42
Other non linear effects
Magnetic field: force ∝ B2
Electric field : force ∝ E2
July 21, 2002-4th LISA Symposium S. Vitale 43
LISA SMART-2 Ref. Num. Requirement
IS S/C IS LTP S/C
1 Magnetic field
maxB
(µT) 3 4 3 3 4
2 Magnetic field gradient ( )x y,zB
x(y, z)
∂
∂
(µT/m)
4 3 4 35 31
3 Magnetic field fluctuation BS
(nT/√Hz) 71 71 71 353 353
4 Magnetic field gradient PSD B xS∂ ∂
(µT/m)/√Hz 0.71 0.71 0.71 3.5 3.5
July 21, 2002-4th LISA Symposium S. Vitale 44
Table 1 DC force requirements
Ref num Case Fx/m (ms-2) Fz/m (ms-2)
1
LISA Electrostatic
suspension on sensitive axis
TBD TBD
2
LISA No electrostatic suspension on sensitive axis
10-9 (limited by thrusters)
TBD
IS LTP S/C IS LTP S/C
3
SMART-2 Important notice: in M1 the figure
includes the effect of S/C acceleration
along x on TM2
2.5×10-10 2.5×10-10 2.5×10-10 0.35×10-9 0.35×10-9 0.8×10-9
July 21, 2002-4th LISA Symposium S. Vitale 45
The special case of gravitational force
Accuracy requirements
112
mg 10s
−−∆ ≈
Gradients, cross-coupling 1%
1 2 6g
5
S 3 10 1 Hz LISAg 3 10 1 Hz SMART-2
−
−
×≤
×
July 21, 2002-4th LISA Symposium S. Vitale 46
Point-like approximation for test-mass breaks down for close sources
Analytical formula found for point-like source and parallelepiped test-mass
( )sF F r=Force
sr
Source
COM ( )s
s
dF rdr
Γ = −Gradient
COM sT r F= ×Torque
( ) ( )s sˆ ˆ r∂ = φ × − φ ⋅ × ∇
∂φAngular derivatives
Analytical formula for F Analytical formula for everything
July 21, 2002-4th LISA Symposium S. Vitale 47
A sample spacecraft
Errors infield
estimate
July 21, 2002-4th LISA Symposium S. Vitale 48
Non-homogeneous “boxes”
July 21, 2002-4th LISA Symposium S. Vitale 49
Table 1 Recommended values for gravitational field requirements verification Parameter Element Value Parameter Element Value
LTP/DRS 10-3kg Attitude error All elements 0.3° Inner and radial
panels 10-3 kg LTP/DRS 0.5 mm Mass Boxes and outer
panels 5 10-3kg LTP-OB 0.2 mm
LTP- OB 5 mm
Location error
All other elements 1 mm
DRS and LTP IS2 1 cm LTP and DRS elements.
Boxes, Inner panels, radial panels
10%
Inner and radial panels 3 cm
Uncertainty on mass distribution
Heavy structural elements, LTP-OB 2%
Mesh size
Outer panels and boxes 4 cm
July 21, 2002-4th LISA Symposium S. Vitale 50
12
34
July 21, 2002-4th LISA Symposium S. Vitale 51
Table 1 Summary of gravitational balance calculation results
Configuration
Mass (kg)
Minimum meshing
(mm)
Homogeneity(%)
Position (µm)
Attitude(°)
Mass uncertainty
(kg)
Resulting gradient
(s-2) 1 6.25 4 2 50 0.5 10-3 6.9×10-7 2 18.06 4 2 100 0.5 2×10-3 7.5×10-8
3 1.29 2 5 50 0.5 5×10-4 1.2×10-6 4 2.78 2 5 50 0.5 5×10-4 4.9×10-8
July 21, 2002-4th LISA Symposium S. Vitale 52
It’s not the complete story
July 21, 2002-4th LISA Symposium S. Vitale 53
Charging
Random arrival of charge on test-mass
July 21, 2002-4th LISA Symposium S. Vitale 54
Charge interacts with stray dc voltage
Random force
July 21, 2002-4th LISA Symposium S. Vitale 55
The random part
( ) 1 21 216 V
12o eff
S m 15 mm 0.1mHz3.7 10m 5 mV 16 s fs Hz
−−
ω σ λ = ×
tot eff toteff eff
C d C Cd 15mmC 2 mm 7
≈ =
λ TBC poor margin: aim at largest gap
(in all directions)
July 21, 2002-4th LISA Symposium S. Vitale 56
July 21, 2002-4th LISA Symposium S. Vitale 57
The LTP key elements: 1 the displacement sensor
Ac bias
Test mass
injection electrode Ac amplifier
PSD
x
y
z
θ
φ
η
θ & y
η & x
φ & z
July 21, 2002-4th LISA Symposium S. Vitale 58
Top and Bottom
Lids
Central frame
Test Mass
Electrodes
July 21, 2002-4th LISA Symposium S. Vitale 59
July 21, 2002-4th LISA Symposium S. Vitale 60
July 21, 2002-4th LISA Symposium S. Vitale 61
July 21, 2002-4th LISA Symposium S. Vitale 62
July 21, 2002-4th LISA Symposium S. Vitale 63
July 21, 2002-4th LISA Symposium S. Vitale 64
144mm 174mm
295.2mm
July 21, 2002-4th LISA Symposium S. Vitale 65
Man
uel R
OD
RIG
UE
S -B
erna
rd F
OU
LON
-1
-ES
TEC
Nor
dwijk
-
Febr
uary
2002
-
4FEEU (Front End Electronics Unit) SCHEMATIC
Vd
DVA
DVA
ProofMass
Possens ADC
DAC
DAC
FPGA
Clock
Serialinterface
Power Supply PrimaryPower Line
Computer
5Vrms
MechStop
Inj Elec
+
+
July 21, 2002-4th LISA Symposium S. Vitale 66© Astrium
Nonpolarizing MZ ifo: robust version (3)
The optical bench contains 3 single interferometers to measure:•the distance between the T/Ms x1-x2•the distance between T/M1 and the optical bench x1•a reference phase•tilt of T/M1.
The LTP key elements: 2 optical metrology
Distance between test-mass 1 and test-mass 2
Distance between test-mass 1 and optical bench
2 relative angles between t.m.1 and t.m 2
2 angles of t.m. 1
A test for optical readout
July 21, 2002-4th LISA Symposium S. Vitale 67
AOM bench
July 21, 2002-4th LISA Symposium S. Vitale 68
July 21, 2002-4th LISA Symposium S. Vitale 69
LTP key elements: 3 Control and Software
Drag-free and attitude control for the spacecraft
The spacecraft cannot follow both test-masses at once
Actuation needed on 1 test-mass also along the sensitive axis
July 21, 2002-4th LISA Symposium S. Vitale 70
LTP is an automous dynamical system
Force noisemodel
Mq-1 1/s2
Electrostaticreadoutmodel
IS noise
Electrostaticsuspension
Laserreadoutmodel
Interferometernoise
fnoise
q*q*..
factuation
Kh
Spacecraftmotion
Spacecraftdistortion
CSC
Mu
nSC
u..
LTP modelS/Cmodel
fho,fLTPo
Sensit. to noise(Bfhf,BfLTPf)
Fsc
Fsc
Drag free control and actuation system
KLTP
q
CLTP
LTPdistortion
nLTP
-
Bfhf
BfLTPf
q
q̂
q
July 21, 2002-4th LISA Symposium S. Vitale 71
Compensating negative stiffness kp= 10-7 N/m
1.¥ 10-6 0.00001 0.0001 0.001 0.01
10
100
1000
10000
parasitic
Gk
frequency[Hz]
p 5k1 5 10 Hz2 m
−= ×π
and dc forces
10-10N/10-7 N/m 1 mm
July 21, 2002-4th LISA Symposium S. Vitale 72
Optimised control
Robust against knowledge of parameters
July 21, 2002-4th LISA Symposium S. Vitale 73
Numerically implementable as ARMA
July 21, 2002-4th LISA Symposium S. Vitale 74
DC comp. a
DC comp. b
TM stabiliz a
TM stabiliz b
SCIENCE MODE
Suspension c
ACCELEROMETER MODE
Low frequency sine wave
Charge measurement
dither
Poles, zeroes, gain
Suspension switchx1,…,x6
Transfer functions
parameters upload
Threshold detector
Caging command
Charge measurement
command
Ch1, ch2,…
External command
DC force offsets
Fd1,…, Fd6
Capacitive actuation functional block diagram
Suspension d
LARGE AMPLITUDE MODE
TBC
Transfer functions selection
Channels combinator
Calibration parameters
upload
July 21, 2002-4th LISA Symposium S. Vitale 75
DC comp. a
DC comp. b
TM stabiliz a
TM stabiliz b
SCIENCE MODE
Suspension c
ACCELEROMETER MODE
Low frequency sine wave
Charge measurement
dither
Poles, zeroes, gain
Suspension switchx1,…,x6
Transfer functions
parameters upload
Threshold detector
Caging command
Charge measurement
command
Ch1, ch2,…
External command
DC force offsets
Fd1,…, Fd6
Capacitive actuation functional block diagram
Suspension d
LARGE AMPLITUDE MODE
TBC
Transfer functions selection
Channels combinator
Calibration parameters
upload
July 21, 2002-4th LISA Symposium S. Vitale 76
DC comp. a
DC comp. b
TM stabiliz a
TM stabiliz b
SCIENCE MODE
Suspension c
ACCELEROMETER MODE
Low frequency sine wave
Charge measurement
dither
Poles, zeroes, gain
Suspension switchx1,…,x6
Transfer functions
parameters upload
Threshold detector
Caging command
Charge measurement
command
Ch1, ch2,…
External command
DC force offsets
Fd1,…, Fd6
Capacitive actuation functional block diagram
Suspension d
LARGE AMPLITUDE MODE
TBC
Transfer functions selection
Channels combinator
Calibration parameters
upload
July 21, 2002-4th LISA Symposium S. Vitale 77
Accelerometer mode
High damping, large force
( )2 2
122 2 2 1a o 2
2 212
2
sss ss
+ + ωω τω = ωω + + ω
τ
max2
F m0.15m s−
µ≤
July 21, 2002-4th LISA Symposium S. Vitale 78
Transition to-from accelerometer mode
Requested to damp long term transitory
Needs adjustment of long term behaviour
July 21, 2002-4th LISA Symposium S. Vitale 79
Test-mass acquisition
July 21, 2002-4th LISA Symposium S. Vitale 80
DC comp. a
DC comp. b
TM stabiliz a
TM stabiliz b
SCIENCE MODE
Suspension c
ACCELEROMETER MODE
Low frequency sine wave
Charge measurement
dither
Poles, zeroes, gain
Suspension switchx1,…,x6
Transfer functions
parameters upload
Threshold detector
Caging command
Charge measurement
command
Ch1, ch2,…
External command
DC force offsets
Fd1,…, Fd6
Capacitive actuation functional block diagram
Suspension d
LARGE AMPLITUDE MODE
TBC
Transfer functions selection
Channels combinator
Calibration parameters
upload
July 21, 2002-4th LISA Symposium S. Vitale 81
DC comp. a
DC comp. b
TM stabiliz a
TM stabiliz b
SCIENCE MODE
Suspension c
ACCELEROMETER MODE
Low frequency sine wave
Charge measurement
dither
Poles, zeroes, gain
Suspension switchx1,…,x6
Transfer functions
parameters upload
Threshold detector
Caging command
Charge measurement
command
Ch1, ch2,…
External command
DC force offsets
Fd1,…, Fd6
Capacitive actuation functional block diagram
Suspension d
LARGE AMPLITUDE MODE
TBC
Transfer functions selection
Channels combinator
Calibration parameters
upload
July 21, 2002-4th LISA Symposium S. Vitale 82
Com
man
d
V1,…, V12F to V
conversion2
F to V conversion
2
Switch
Capacitive model equation
parameters upload
Carrier waveform parameters
upload
Capacitive actuation
1
Fd1,…, Fd6
Carrier waveform synthesis
3
ISFEE DAC
4
TM
Optical metrology
Capacitivesensing
V1(t)..V12(t) forces
ADC
Switch Commandx1,…,x6ADC
July 21, 2002-4th LISA Symposium S. Vitale 83
Com
man
d
V1,…, V12F to V
conversion2
F to V conversion
2
Switch
Capacitive model equation
parameters upload
Carrier waveform parameters
upload
Capacitive actuation
1
Fd1,…, Fd6
Carrier waveform synthesis
3
ISFEE DAC
4
TM
Optical metrology
Capacitivesensing
V1(t)..V12(t) forces
ADC
Switch Commandx1,…,x6ADC
July 21, 2002-4th LISA Symposium S. Vitale 84
Actuation by frequency modulation of carrier
To suppress thermal noise and charge effect by suppressing dc-voltages
July 21, 2002-4th LISA Symposium S. Vitale 85
Com
man
d
V1,…, V12F to V
conversion2
F to V conversion
2
Switch
Capacitive model equation
parameters upload
Carrier waveform parameters
upload
Capacitive actuation
1
Fd1,…, Fd6
Carrier waveform synthesis
3
ISFEE DAC
4
TM
Optical metrology
Capacitivesensing
V1(t)..V12(t) forces
ADC
Switch Commandx1,…,x6ADC
July 21, 2002-4th LISA Symposium S. Vitale 86
12
4
35 6
8 7
10
9
1314
11
12x
y
z
Force to voltage conversion
1 carrier frequency per DOF DOF are independent
Test-mass V=0No-cross-talk
x ox
K df2
≤Max force
L
x
φ
Force,no torque
Constant stiffness
linear control
July 21, 2002-4th LISA Symposium S. Vitale 87
©Astrium90 Smart-2 Final Presentation 12/07/2002
Frequency Analysis – X axis acceleration (1 of 3)
10-4 10-3 10-2 10-110-14
10-13
10-12P S D totaleFx1 force nois eFy1 force nois eFz1 force nois eTheta1 force nois eEta1 force nois eP hi1 force nois eFx1 readout nois eFy1 readout nois eFz1 readout nois eTheta1 readout nois eEta1 readout nois eP hi1 readout nois e
July 21, 2002-4th LISA Symposium S. Vitale 88
LTP key elements 4: Monitoring the environment
MagnetometerParticle detector
+ solar radiation monitor
July 21, 2002-4th LISA Symposium S. Vitale 89
Pulling all together
July 21, 2002-4th LISA Symposium S. Vitale 90
LTP Sensor / Optical Bench / Structure Architecture
July 21, 2002-4th LISA Symposium S. Vitale 91
July 21, 2002-4th LISA Symposium S. Vitale 92
July 21, 2002-4th LISA Symposium S. Vitale 93
July 21, 2002-4th LISA Symposium S. Vitale 94
July 21, 2002-4th LISA Symposium S. Vitale 95
July 21, 2002-4th LISA Symposium S. Vitale 96
< 85 kg
July 21, 2002-4th LISA Symposium S. Vitale 97
< 110 W
July 21, 2002-4th LISA Symposium S. Vitale 98
LTP main boxMass = 43 kgPower = <0.1WDimensions = 600mm (length)
354 mm(diameter)
IS-FEE #1Mass = 3.5kgPower = 7.4 WDimensions =240x200x170mm
IS-CMS electronics+UV lampMass = 6 kgPower = 8(0.8)W (quiescence)Dimensions = 165x130x60mm
IS-CM electronicsMass = 1 kgPower = 18WDimensions = 240x150x20mm
Processor and diagnosticsMass = 4.2kgPower = 35 WDimensions = 260x200x80mm
Phase detector FEEMass = 1 kgPower = 15 WDimensions =200x200x100mm
Laser systemMass = 5 kgPower = 20 WDimensions =150x200x200mm
S/C Power
IS-FEE #2Mass = 8.5kgPower = 7.4WDimensions =240x200x170mm
28V PowerRS 422Electrical wireOptic fiber
MagnetometerMass = 0.5 kgPower = 0.6 WDimensions = 45x143x80mm
Particle DetectorMass = 2.5 kgPower = 2.6 WDimensions = 95x122x217mm
AOM Mass = 2 kgPower = 15 WDimensions =200x200x100mm
To S/C bus
July 21, 2002-4th LISA Symposium S. Vitale 99
A key element for the test: micropropulsion
July 21, 2002-4th LISA Symposium S. Vitale 1008-04-2002-DRS LTP Meeting S. Vitale 80
SMARTSMART--22 LTPLTP--ArchitectArchitect
July 21, 2002-4th LISA Symposium S. Vitale 101
©Astrium29 Smart-2 Final Presentation 12/07/2002
LISA satellite
• Dedicated LISA spacecraft forms basis of mission- Dedicated internal space for separate LTP and DRS
panels allows orientation of sensitive axes as required.
- Height 900mm overall- Communications antennas positioned for L1 orbit,
two 5cm X-band horns provide overlapping coverage. X-band patches for omni coverage
• Simultaneous operation of LTP and DRS accommodated by oversizing solar array (2 m2. )
- Solar panel also mounts antennas, sensors, lifting points
- Some scope to increase sunshield diameter for top spacecraft, but 2m constraint used
• This configuration is the basis for all detailed structural, thermal, GNC analyses carried out in phase 3 LISA satellite includes cold gas for station
keeping, plus 4 FEEP clusters
LTP and DRS stacked for independent axis alignment
July 21, 2002-4th LISA Symposium S. Vitale 102
©Astrium156 Smart-2 Final Presentation 12/07/2002
Structural Design
• Structure design based on filament wound octagonal facetted cylinder
- Diameter and taper easily variable
• Concept designed and tested for launch stacked using pyro bolt attachments
- STM Statically tested to loads equivalent to stack above 800kg
- Sine tested above 350kg- Extensive correlation provides
confidence in FE modelling
• Very stable and low distortion structure, with few parts to minimise hysteresis
- Equipment simply bolts through
July 21, 2002-4th LISA Symposium S. Vitale 103
©Astrium19 Smart-2 Final Presentation 12/07/2002
Orbit options
• Extensive range of orbits studied, and missions to each designed:- Geostationary- Highly elliptical- Weak stability (new set of “stable” orbits described)- Earth-Sun Lagrange points- Heliocentric drift away orbits
• Geostationary and HEO options place strong constraints on technology demonstration
• WSB, Lagrange and Drift-away orbits all special cases of family which provide excellent conditions for the demonstrations
• Lagrange point orbits provide the best combination of communications and thermal stability
- L1 chosen for easiest compatibility with Ariane launch.
July 21, 2002-4th LISA Symposium S. Vitale 104
©Astrium20 Smart-2 Final Presentation 12/07/2002
Launch options, via GTO or similar medium altitude intermediate orbit
• For missions from the Ariane 5 standard GTO, the required velocity increment to raise the apogee to 1.3 million km is about 760 m/sec.
• An Ariane 5 launch requires:- After apogee raising, orbit insertion manoeuvres of up to
110 m/sec to reach a baseline 1000000km radius halo orbit. - Implies limited launch window restrictions in May/June to
avoid excess DeltaV overhead
- Total transfer dispersion corrections/losses are approximately 20 m/s
Launch vehicle injects intointermediate orbit
Mult iple burns to
raise apogee to L1
Injection intoHalo orbit
Approx 2 million km
View on ecliptic
July 21, 2002-4th LISA Symposium S. Vitale 105
S M A R T - 2
Mission Definition Study
PHASE 3
Page 16Final ReviewFR. ESTEC, Noordwijk, July 11th 2002
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· The LTP experiment
July 21, 2002-4th LISA Symposium S. Vitale 106
· The SAT A experiments and ACS· The SAT A experiments and ACS+POWER· The SAT A experiments and ACS+POWER+ COMMUNICATIONS· The SAT A experiments and ACS+POWER+ COMMUNICATIONS+OBDH
July 21, 2002-4th LISA Symposium S. Vitale 107
S M A R T - 2
Mission Definition Study
PHASE 3
Page 41Final ReviewFR. ESTEC, Noordwijk, July 11th 2002
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· The SAT A experiments and ACS+POWER+ COMMUNICATIONS+OBDH+STRUCTURE AND THERMAL CONTROL
Unit TotalDimensions (mm)
Mass (kg)EquipmentSubsystem #
Power (W)
uN Thrusters Cluster 140 x 140 x 50 4 2,5 10 28uN Thrusters PCU 250 x 165 x 200 4 3,5 14 24Fine & Coarse Sun Sensor 100 x 100 x 20 3 0,5 1,5 2Star tracker 140 (D) x 230 (L) 1 2,5 2,5 10
ACS & Propulsion – Total 28 64
ACS / Propulsion
Solar Array (Solar Cells) 1800 (D) x 70 (t) 1 2,5 2,5 0Battery 160 x 120 x 75 1 2,5 2,5 1PCDU 100 x 270 x 125 1 4,6 4,6 6,5
Power - Total 9,6 7,5
Power
Transponder + Amplifier 275 x 110 x 197 1 6 6 37High gain Antenna 500 (D) x 180 (L) 1 3 3 0Low gain Antenna 6 (D) x 25 (L) 2 0,5 1 0
Communications - Total 10 37
Communications
Computer 236 x 165 x 178 1 6,4 6,4 16RTU 237 x 165 x 128 1 4,7 4,7 6,5
OBDH - Total 11 22,5
OBDH
Structure 1 32,7 32,7 0Bracketery 1 12,3 12,3 0Harness Distributed 1 4 4 7SATELLITE COMPEN MASS 4 7
Structure - Total 56 7
Structure
Heaters / TC Various TBD 1 1 6MLI Various TBD 2 2 0Radiators Various TBD 1 1 0
Thermal Control - Total 4 6
Thermal Control
Satellite A total Mass: 272 kg (nominal) / 292 kg (with margin)
July 21, 2002-4th LISA Symposium S. Vitale 108
S M A R T - 2
Mission Definition Study
PHASE 3
Page 72Final ReviewFR. ESTEC, Noordwijk, July 11th 2002
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- DDVProgrammatic considerations (12/16)M
ore
deta
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info
rmat
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in S
M2-
CA
S-
5400
-TN
O-0
01(1
-Jul
-02)
July 21, 2002-4th LISA Symposium S. Vitale 109
CONSOLIDATION OFLTP DEFINITION
SMART-2
STUDY 2
TWO CONTRACTORS IN PARALLELPERFORM THE
MISSION DEFINITION PHASE
A-PRE B
TODAY
LISA
1.04 12.05 3.07 3.11
DEFIN.B/C/D
ITTITT
6.01
9.01
Preliminary Design Review
3.05 8.115.03
ITT B
Launch
LCC/DB
STUDY 1 2.03
C/D
8.06
10.61.07
LAUNCH
PREPARATION
6.02
6.0611.03
ITT B/C/D ITT
LISADEMOLAUNCH
CAMP.COMMISS.
July 21, 2002-4th LISA Symposium S. Vitale 110
Testing quality of free fall
10-15
10-14
10-13
10-12
FNSHz
Torsion pendulum (surface disturbances)
SMART-2
LISA