Optical metrology applications at TAS-Ieotvos.dm.unipi.it/Workshop2010/Talks/Cesare.pdf · the optical metrology at 10 Hz. Max. measurement error: 0.25 mm (over the largest steps)

GG workshop

12/02/2010 2/26/2008, Thales Alenia Space

Template reference : 100181670S

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INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE

All rights reserved,

Optical Metrology Applications at TAS-I in support of Gravity and Fundamental Physics

Stefano Cesare, Thales Alenia Space Italia, Torino

Workshop “GG/GGG: state of the art and new possibilities”Pisa, 12 Febbraio 2010

2/26/2008, Thales Alenia Space

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Optical metrology at TAS-I

Main research projects and applications of optical metrology at TAS-I:

Monitoring of the GAIA astrometric instrument stability (1997 –2003).Co-phasing of optical interferometers (2002 – 2006).Satellite-to-satellite laser tracking for Next Generation Gravity Missions (2004 – present).Nanobalance facility for characterization of micro-Newton thrusters (2001 – present).

Collaborations:

Istituto Nazionale di Ricerca MetrologicaPolitecnico di TorinoINAF – Osservatorio Astronomico di Torino


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Metrology for GAIA astrometric instrument

0 100 200 300 400-2

-1

0

1

2

3x 10-12

Time [s]

Dis

tanc

e va

riatio

n [m

]

IFR signal: Control error


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Co-phasing of optical interferometers

Breadboard of a two-aperture optical interferometer with its co-phasing system, for the development project of a synthetic-aperture optical telescope. Fringe Sensor Unit realized for the co-phasing of

the VLTI (ESO). Operative at Cerro Paranal, Chile.


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The distance variation between two satellites (∆d) is measured by a laser metrology system.The distance variation between the satellites produced only by drag forces (∆dD) is measured by accelerometers.

Subtracting (∆dD) from (∆d) the distance variation produced by the gravity acceleration is obtained: ∆dG = ∆d - ∆dD

Satellite 2 Satellite 1

g2 g1

d

∆d = ∆dG+ ∆dD

Earth

FD2 FD1D2 D1

Requirement for the laser interferometer measurement noise (relative distance = 10 km)

Satellite-to-satellite laser tracking for NGGM

1 10 4 0.001 0.01 0.1 11 10 9

1 10 8

1 10 7

1 10 6

frequency [Hz]

rela

tive

dista

nce

erro

r SD

[m/s

qrt(

Hz)

]

.1 10 3 10 1

2.26 nm/√Hz

Gravimetry by satellite-to-satellite tracking


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Michelson-type heterodyne laser interferometer based on polarized beams, with chopped measurement beam to avoid spurious signals and non-linearity caused by the unbalance between the strong local beam and the weak return beam.Passive retro-reflection of the laser beam on S2: simple solution, suitable for d up to 100 km.

Optical metrology concept for the NGGM

λ2πδ

21δ φ

=L

ν2

pbs2 q1q2

p4

p3

ν1

p1

p2

RR1

l1

l2

c1

c2

ν2

ν0 ν1

f1

f2νm

ν0

ν'm

pbs1 pd1

bsAMFSLaser source

Frequency StabilisationSystem

BSM telescope

amplitudemodulated beam

RR2

Satellite 2

angle and lateral displacement sensors angle sensors

PSD1

PSD2

PSD3

PSD4

PSD5

PSD6

Satellite 1 pd2

L

Spd2 = 2I”⋅{1 + cos [2π(ν1-ν2)t + φ + δφ]}

Spd1 = 2I’⋅{1 + cos [2π (ν1-ν2)t + φ]}

Nd:YAG

1064 nm


d


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Satellite 2

Active optical bench(laser emission & interferometry)

Satellite 1Passive optical bench(laser retro-reflection)

Accelerometers

Interferometer core

Beam Steering Mechanism

Angular metrology

Angular/lateral metrology

Retro-reflector

Optical metrology arrangement on the satellites

The non-gravitational accelerations of the satellite COM can be measured by electrostratic accelerometers like those used on GOCE.



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Laser interferometer breadboard prepared for the intrinsic noise test (measurement of a constant distance).

Spectral density of the distance variation measurement error obtained during the tests and compared to the requirement.

In order to achieve the specified measurement performance over a distance of 10 km, the laser frequency shall have a relative stability δν/ν ≤ 1.4⋅10-13 Hz-1/2.


Interferometer BB test


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Interferometer BB test

Laser interferometer breadboard under the functional test over a long distance (~90 m) with a moving target. The effectiveness of the measurement beam chopping scheme was successfully verified in this test.



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Open-loop test of the Lateral Displacement Metrology.Lateral displacement steps (from ±50 µm to ±5 mm) measured by the optical metrology at 10 Hz. Max. measurement error: 0.25 mm (over the largest steps)Max. measurement noise: 14 µm 1σ.

Test of the laser beam pointing control system BB.

Beam Steering Mechanism Angle/lateral Displacement

Metrology

Closed-loop test of the laser beam pointing control system (BSM driven by the Lateral Displacement Metrology measurements). Laser beam pointing stability results.



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optical cavity

NanobalanceThrust Stand

optical head

alignmentdevice

thrusterunder test

vacuum chambertiltmeter

pneumaticsupport

horizontality control stage

beam trap

pumpgroup

optical fiber

metrology system

optical benchMonitoring and Control System

thermistor(s)

vacuometer

Thrust Stand

Nanobalance

The Nanobalance is a complete test facility for the direct measurement of the force provided by a micro-thruster along its thrust axis, developed by TAS-I for ESA.


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A micro-thruster force F = 0.1 µN induces a distance variation betweenthe tilting plates δL ≅ 14 pm, corresponding to frequency variation of the laser locked to the Fabry-Perot cavity δνL ≅ 40 kHz.

Fabry-Pérot Cavity, L

elastic jointZERODUR®

Athermicspacer

Micro-Thruster under terst

Laser, vL

Passive Tilting Plate

elastic joint

Dummy Micro-Thruster

Actiive Tilting Plate

Fabry-Pérot Cavity, L -δL

elastic joint

ZERODUR®

Athermicspacer

Micro-Thruster under terst

Laser, vL + δvL

Passive Tilting Plate

elastic joint

Dummy Micro -Thruster

Actiive Tilting Plate

Thrust F

Nanobalance


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Nanobalance

Power Spectral density of the measurement force noise after post-processing for removing the low-frequency drift effect.

10-4 10-3 10-2 10-1 100 10110-3

10-2

10-1

100

101

Frequency [Hz]

PS

D [ µ

N/ √

Hz]

10-4 10-3 10-2 10-1 100

Forc

e [µ

N/√

Hz]

Frequency [Hz]

100

101

10-1

10-2

10-3

NB background noise - PSD

10170 80 90 100 110 120 130

-0.2

0

0.2

0.4

0.6

0.8

1

Time [s]

Forc

e [ µ

N]

VC forceWide band filterNarrow band filter

NB Resolution

Applied ForceWide band meas.Narrow band meas.

Measured thrust corresponding to the smallest applied force steps with a voice coil actuator.


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Nanobalance

Test of a cold-gas thruster

Applications:GAIA, Microscope (backup)

Applications:LISA PF, Microscope,GG

Test of a FEEP thrusterTest of a mini-RIT

Applications:NGGM, GG (backup)

Documents

Optical metrology applications at TAS-Ieotvos.dm.unipi.it/Workshop2010/Talks/Cesare.pdf · the optical metrology at 10 Hz. Max. measurement error: 0.25 mm (over the largest steps)