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FISICA
Far Infrared Space Interferometer Critical Assessment
Science Goals of a Sub-arcsecond Far-infrared Space
Observatory
FISICA: engineering problems and system requirements for
interferometric observations from the space
Valerio Iafolla (AGI, Roma, Italy)
17-18th Feb. 2014, Aula Marconi, National Council of Research,
Piazzale Aldo Moro 7, Roma
V. Iafolla
17 Feb 2014
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In this talk will be analyzed some technological problems related to the
interferometer development, with particular emphasis in the possible use of
accelerometers on board of the satellites that seems to offer the following
opportunity:
!  to implement a control loop algorithms to keep the satellites in the appropriate
positions during the observation time required to cover all the u,v plane, for
each single source
!  to permit to measure the level of vibrational noise presents on them.
The heritage for these activities comes from the developments of the
ISA (Italian Spring Accelerometer) an accelerometer conceived for the
BepiColombo an ESA Cornerstone mission for the exploration of Mercury and to
test the General Relativity.
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m/s 2
Acceleration in the Euler Reference Frame
1000
2.38176e-10
800
600
1.9848e-10
400
1.58784e-10
meters
200
0
1.19088e-10
-200
-400
7.9392e-11
-600
3.9696e-11
-800
-1000
​" +2​$ ↓0 ×​" +​$ ↓0 ×​" ​+​$ ↓0 ×(​​$ ↓0 ×​
" )=(∙​" -1000
-500
0
meters
500
1000
Accelerations in the Euler reference frame
in L2, due to the gravity gradient.
Orbital Trajectory for tw o satellites in Euler-Hill reference frame
data1
data2
800
2000
600
1800
400
1600
0
meters
meters
200
-200
-400
1400
-600
1200
-800
-1000
-500
0
meters
500
1000
Two satellites out of phase by 180 ° in a Euler non-inertial
reference frame.
1000
0
0.5
1
1.5
2
Seconds
2.5
3
3.5
7
x 10
Relative distance between the two satellites
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​) =(​*∙ ​+ )​, −​$ ×(​$ ×​, )−​$ ×​, −2​$ ((x(​- −​
.↓/(0 −​∆​1 /∆3 |↓5)6 1.
2.
3.
4.
Accelerations due to gravity gradients
Apparent accelerations
Non–gravitational accelerations (NGA),
Accelerations due to thruster maneuvers
Free-flyer
Tethered
Rigid Structure
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Due to the conservation of the angular momentum, a change in the radial distance
of interferometer telescopes results in a change of their associate angular and
tangential velocity
20
10
0.8
30
0.2
2
4
6
8
time
10
4
x 10
Accelerations
0.04
linear 0
0
square
cubic
root
15
exponential
0.03
0.02
4
6
time
8
10
4
x 10
steps
0
0
2
4
6
time
8
10
-20
20
-30
10
-40
-50
-50
-10
50
-20
40
-30
30
-40
20
-50
-50
0
exponential
50
0
m
50
m
10
0
m
50
0
-10
50
10
cubic
-20
-30
40
-40
30
5
0
-50
-50
20
m
0.01
2
30
0
m
20
0.4
40
-10
linear squarecubic root
exponential
4
x 10
The five trajectories. In red linear law, in green the square, in blue
the cubic, in yellow the square-root and in cyan the exponential
one.
10
50
0
40
-10
30
root
20
-20
10
-30
m
[m/s]
0.6
meters
[m/s 2]
meters
40
0
m
square
50
0
30
Velocities
50
10
40
m
Radius
linear
50
-40
0
-10
-50
-50
0
m
50
-20
-30
-40
-50
-50
0
m
50
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In order to have a constant tangential velocity along a spiral trajectory, the system
should change its angular momentum continuously during the manoeuvres whit the
use of thrusters.
Needed Torque w rt maneuver time
0.055
Spiral Trajectory for a thrusted assiste maneuver
Radius
50
0.05
45
0.045
40
0.04
30
35
0.035
meters
Torque [Nm]
40
0.03
25
0.025
20
20
0.02
15
0.015
0
0.01
10
0
0.2
0.4
0.6
0.8
1
[s]
1.2
1.4
1.6
1.8
0
0.2
0.4
0.6
0.8
1
seconds
1.2
1.4
1.6
1.8
2
5
x 10
2
5
x 10
-10
-6
0
-5
Normal accelerations
x 10
16
Radial accelerations
x 10
-20
14
-0.5
-30
12
-1
m/s 2
10
-40
m/s 2
[m]
10
30
-1.5
8
-60
-40
-20
0
[m]
20
40
60
-2
6
-2.5
-3
0
4
0.2
0.4
0.6
0.8
1
seconds
1.2
1.4
1.6
1.8
2
5
x 10
2
0
0.2
0.4
0.6
0.8
1
seconds
1.2
1.4
1.6
1.8
2
5
x 10
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Simulation of the process of scanning of the uv plane with radial movements of the
telescopes of 1m after every rotation 180° of the interferometer.
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Interferometer)Band)of)measure)(Science)Light))
!"#$:&[()*# &&()"+ ] = [25&0)&&5000)])
)
If) it) is) decided) that) the) max) distance) related) to) the) largest) wavelength) is) performed) by) the) ODL) in) 26) s,) it)
follows)a)speed)equal)to:)
)
)
10−6
23 = &500 ∙
= 1.9& ∙ 10−5 )/3)
26
From)this)condition)the)frequency)band)in)which)we)are)working)is:))
)
!"#$:&&[;)"+ &&;)*# ] = [23 /()*# &&23 /()"+ ] = [6.4 ∙ 10−1 =>&&&&3.8 ∙ 10−2 =>]&)
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7=7(B)
7(B)=​7↓0 ∙cos(2∙C/​9↓< ∙(​1↓0 ∙3+​=↓> ))
​7↓0 !
​9↓0 !
​3↓0 !
​ 1 ↓ 0 =​
9↓0 /​3↓0 !
​9↓< !
​=↓> !
​10↑−6 !
500(:;!
26(<!
1.9(∙(​10↑−5 (;/<!
1/5∙​10↑4 =20∙​10↑−6 !
​ 10↑−3 ​ ;/√⁠@A (−( ​ 10↑
−11 (;/√⁠@A - !
Results of a simulation relative to the acquisition of an interferometric signal
considered as simple sinusoid, in the case of the parameter reported in the previous
table. The level of white noise considered for the displacement is 10^-6 m/sqr(Hz)
black; 10^-8 m/sqr(Hz) Ciano, 10^-9 m/sqr(Hz) Magenta, 10^-10 yellow, 10^-11 m/
sqr(Hz) blue. Green represent the fft of the sinusoid acquired without jitter noise.
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D)6E:(([​G↓;)= ((​G↓;H6 ]=[​1↓< /​B↓;H6 ((​1↓< /​B↓;)= ]=[26/30:−26/500:=[6.4∙​
10↑−1 @A((((3.8∙
​10↑−2 @A](
Vibrational**noise*inside*the*frequency*measurements*band*on*board*the*
MPO*(Mercury*Planetary*Orbiter)*BepiColombo*Mission*for*the*RSE*(Radio*Science*Experiments)*
!
Frequency Hz
! ∙ #$−&
#$−'( − ( #$−!
#$−#
Acceleration values ()/+, )
3 ∙ 10−9 !
10−9 − ( 10−9 !
10−4 !
8.4 ∙ 10−2 !
2.5 ∙ 10−3 − (2.5 ∙ 10−5 !
2.5 ∙ 10−8 !
Corresponding
displacements m
!
The!acceleration!values!between!the!indicate!points!are!linearly!connected!,!while!the!displacements!
values!can!be!found!using!the!relation:!6 = 8/(2 ∗ ;< ∗ =)^2!
ASTRIUM ASSESSMENT
Noise presents on the MPO
BepiColombo due to the
motions of the solar array.
Analogue noise are due to the
HGA and Reaction Wheels
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10-10 g/Hz1/2
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Sensitivity!
1e-7 - 1e-8 g/sqrt(Hz)!
Acquisition frequencies (Hz)!
0.1,0.2,0.5,1,5,10,20,50,100 !
Output !
Analogic or digital!
Data rate (10Hz one acc. And one T)
[byte/s]!
250 !
​ 10↑−4 Internal thermometer Pt10000!
Precision better than
°C!
Interface of communication!
Rete RS232 full-duplex/Rete
RS485 (con adattatore)!
Standard of communication!
NMEA!
Dimensions of a single axis
mechanical element !
80 x 60 x 25 (H x L x A)!
Electronic dimensions for a single
element [mm]!
75X55X12!
Voltage supply via USB or external
[V]!
5!
Power dissipation!
75 mW!
Weighs [Kg]!
0.200!
Linearity!
> 80 dB!
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Conclusions
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