LISA Pathﬁnder - CSIC on board LISA Pathﬁnder • The LISA Technology Package (LTP) • European...

LISA Pathfindermeasuring pico-meters and femto-Newtons in space

M Hewitson for the LPF teamBarcelona, February 15th 2012

Wednesday, February 15, 12

M Hewitson, LPF, Barcelona, 15th Feb 2012

Observing from Space

2Wednesday, February 15, 12



• Push down to much lower frequencies: mHz





• Stability of ground-based instruments is difficult to achieve at these frequencies• seismic wall ~10 Hz






• Going to space:• Increase arm-length (increase sensitivity, ∆L/L )






• Going to space:• Increase arm-length (increase sensitivity, ∆L/L ) • Quite environment (reduce noise)



LISA concept



LISA concept

3

SC

Telescope

OB

OB

PM

PM

GRS

GRS

Thruster

Thruster

Thruster

Thruster

Thruster

Thruster Telescope



LISA concept

3

SC

Telescope

OB

OB

PM

PM

GRS

GRS

Thruster

Thruster

Thruster

Thruster

Thruster

Thruster Telescope

GRAVITATIONAL REFERENCE SENSOR (GRS) Test Mass + Drag free



LISA concept

3

SC

Telescope

OB

OB

PM

PM

GRS

GRS

Thruster

Thruster

Thruster

Thruster

Thruster

Thruster Telescope


OPTICAL METROLOGY Optical Bench (OB) + Phasemeter (PM)



LISA concept

3

SC

Telescope

OB

OB

PM

PM

GRS

GRS

Thruster

Thruster

Thruster

Thruster

Thruster

Thruster Telescope


OPTICAL METROLOGY Optical Bench (OB) + Phasemeter (PM)

THRUSTER



LISA Measurement -> LISA Pathfinder



LISA Measurement -> LISA Pathfinder

4

a longway



The LISA Pathfinder Mission

• Technology demonstrator for a LISA-like mission:• Local interferometry• micro-Newton propulsion• Gravitational Reference Sensor• Drag-free control

• LPF will be placed in orbit around L1• Requirements relaxed

• 1 order of magnitude in differential acceleration• LPF req. 3x10-14 m/s2 @ 1mHz

• 1 order of magnitude higher frequency• LPF meas. bandwidth 1mHz < f < 30mHz



The LISA Pathfinder Team

6

Netherlands: - ISS SCOE

Germany: - Co-Principle Investigator - LTP Architect (Astrium)- Laser

Switzerland:- ISS Front End Electronics

Italy: - Principle Investigator - Inertial Sensor- Caging Mechanism

United Kingdom: - Optical Bench- Phase-meter - Charge Management

France:- Laser modulator

Spain: - Data Diagnostics System- Data Management Unit



Payloads on board LISA Pathfinder

• The LISA Technology Package (LTP)• European payload• Full system

• thrusters, test-masses, inertial sensor, interferometers, etc

• The Disturbance Reduction System (DRS)• NASA payload• Alternative thrusters• Alternative drag-free control



The LISA Technology Package (LTP)



x-axis measurement



IFO X1: SC-TM1 measurement



Drag-free on TM1



IFO X12: TM1-TM2 displacement



Suspension control



Spacecraft



.



The LTP



The LTP

16

Reference Laser Unit

Data Management Unit

Phasemeter

Optical Bench

Vacuum EnclosureInertial Sensor


M Hewitson, LPF, Barcelona, 15th Feb 2012 17Wednesday, February 15, 12


Current status (what’s missing?)



Current status (what’s missing?)• Micro-propulsion system

• problems with Ca FEEPs in the past• may now be solved

• ESA have been looking at alternative systems• modified Ca FEEPs, Indium FEEPS, Cold gas,

mini-RIT, Colloid• further testing to be done before deciding on a

solution



Current status (what’s missing?)• Micro-propulsion system

• problems with Ca FEEPs in the past• may now be solved

• ESA have been looking at alternative systems• modified Ca FEEPs, Indium FEEPS, Cold gas,

mini-RIT, Colloid• further testing to be done before deciding on a

solution

• Caging mechanism• Construction of original launch-lock proved

challenging• ESA investigating alternatives

• New cam-based system, single-shot mechanism• single-shot mechanism has been selected



Testing: On-station Thermal Tests

• Uses a thermal-optical qualification model in place of the flight LTP• Consists of a flight optical bench, with flight mounting

struts, and thermal mass dummies of the inertial sensors



Testing: On-station Thermal Tests

• Uses a thermal-optical qualification model in place of the flight LTP• Consists of a flight optical bench, with flight mounting

struts, and thermal mass dummies of the inertial sensors

19

Alberto Lobo’s talk



Science Goals



Science Goals

• Obtain the best geodesic motion possible• quietest differential acceleration of the two TMs

• 3 x 10-14 m s-2 /√Hz at 1 mHz• pm accuracy position measurement of TM-SC, TM-TM

• commissioning by changing system parameters• determine best configuration by experiments



Science Goals

• Obtain the best geodesic motion possible• quietest differential acceleration of the two TMs

• 3 x 10-14 m s-2 /√Hz at 1 mHz• pm accuracy position measurement of TM-SC, TM-TM

• commissioning by changing system parameters• determine best configuration by experiments

• Develop a noise model of the system• allows the projection of the performance of

technologies to LISA



Mission Operations

• We have 90 days to achieve the goals• characterise and optimise the system

• All days are filled with pre-planned experiments• some flexibility is built-in

• Data analysis of the experiments will be done in real-time



Experiments

22

• Technical studies are broken down into investigations

• These investigations are then packed into the time-line

Measurement of Parasitic Voltages

Measurement of differential acceleration noise on LISA Pathfinder

Measurement of cross-talk between the y-axis and the x-axis on the LTP

Measurement of LTP dynamical coefficients by system identification

Analysis of Data from the Radiation Monitor on LISA Pathfinder

Thermal experiments on board the LTP

Magnetic experiments on board the LTP

OPD noise investigations for LTP

Laser frequency noise characterisation for LTP

Laser Amplitude Noise Characterisation for LTP

The Drift Mode for LISA Pathfinder



Estimating residual differential TM acceleration (1)

• The direct observables of the instrument are displacements

• We need to estimate residual forces acting on the TMs

• We can:• estimate acceleration of the SC

• derived from SC-TM1 displacement• estimate differential acceleration of two TMs

• derived from differential displacement of two TMs




24

�DS�1 �C

⇥⇤o = ⇤A + DS�1⇤on




24

�DS�1 �C

⇥⇤o = ⇤A + DS�1⇤on

observationnoise




24

�DS�1 �C

⇥⇤o = ⇤A + DS�1⇤on

observationnoiseresidual

acceleration




24

�DS�1 �C

⇥⇤o = ⇤A + DS�1⇤on


acceleration

measurement




24

�DS�1 �C

⇥⇤o = ⇤A + DS�1⇤on


acceleration

measurement

system




24

�DS�1 �C

⇥⇤o = ⇤A + DS�1⇤on

⇥A

⇥on

⇥o

S

C

D�1



Parameter estimation

• Employ different estimation methods to work with multiple inputs, multiple outputs

• All methods require a parametric model of the system


0 0.5 1 1.5 2 2.5 3x 104

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LinearNonlinearMCMC



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LinearNonlinearMCMCData


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4 x 10−9 Time origin: 2010−04−23 07:36:36.000 UTC

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LinearNonlinearMCMC



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0 0.5 1 1.5 2 2.5 3x 104

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3 x 10−8 Time origin: 2010−04−23 07:36:36.000 UTC

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LinearNonlinearMCMCData

10−4 10−3 10−2 10−1 10010−12

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tral

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sity

[m

Hz−

1/2 ]

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LinearNonlinearMCMCNoise o_12



Results using mission simulator

• We can simulate experiments using the mission simulator• 3D, non-linear, time-domain simulation

• We can recover the parameters with high precision• very dependent on having a good model


M Hewitson, LPF, Sheffield, 13th September 2011 28

Data Analysis



Data Analysis

•DA Software• Toolbox of algorithms to act on the data• Repository for storing data products• Client for submitting and retrieving to/from repository• Documentation and testing



Data Analysis


•DA Activities• Simulate experiments• Design, build and test analyses and associated tools• Train scientists



Data Analysis


•DA Activities• Simulate experiments• Design, build and test analyses and associated tools• Train scientists

LTPDAhttp://www.lisa.aei-hannover.de/ltpda/


http://www.lisa.aei-hannover.de/ltpda/

http://www.lisa.aei-hannover.de/ltpda/


Noise budget

• Various noise contributions can be directly measured

• Some noise couplings must be modelled• using estimates of physical parameters together with

a system model• Some noise contributions must be estimated/

modelled from design



Requirements Differential Force Noise Budget



Free-flight experiment




• Capacitive actuation will be close to limiting around 1mHz





• Do an experiment with the actuation off• must be short otherwise the TM will drift too far• repeat many times





• Do an experiment with the actuation off• must be short otherwise the TM will drift too far• repeat many times

• Experiment:• kick test-mass away• turn off actuation• let the test-mass drift (in parabola)• repeat



Simulation



PSD Estimate

33

Simulation with requirement-level noises but x3 reduced direct TM

force noise



Towards s/LISA/%s



Conclusion• LPF is well on its way!

• Most of the hardware is there• awaiting thrusters and

launch lock• Most of the

experiments are already defined• many are even tested

with DA in place• We have a clear path

to launch• Launch in 2014


M Hewitson, LPF, Barcelona, 15th Feb 2012 36

Thank you


LISA Pathﬁnder - CSIC on board LISA Pathﬁnder • The LISA Technology Package (LTP) • European...

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