Past, present and future Past, present and future ofof Gravitational WaveGravitational Wavedetectiondetection Science Science

J. Alberto Lobo, Bellaterra, 13-October-2004

Presentation summary

1. Current GW detection research status:

• Acoustic detectors

• Interferometers

• LISA

2. LPF and the LTP

3. The Diagnostics and DMU subsystems

4. Future prospects

Earth based GW detectors

There are two detection concepts at present

Acoustic detection:

Interferometric detection:

Based on resonant amplification of GW induced tidal effects.

Based on GW induced phase shifts on e.m. waves.

VIRGO, LIGO, GEO-600, TAMA

EXPLORER, NAUTILUS, AURIGA, ALLEGRO, NIOBE

Bar concept

Idea of an acoustic detector (bar) is to link masses with a spring:

so that

202 ( ) ( )

1( )( ) (

2)l t l t l ltl ht t

and GW signal gets selectively amplified around frequency .

202 ( ) ( )l t l t l

2co( , ) ( , )s sin n) i2 s( 2h t h t h t 0 0x x Strongdirectionality

Real bar detectors

J. Weber

• Two well separated aluminum bars (~1000 km)• Resonance at ~1 kHz• Piezoelectric non-resonant transducers• Impulse sensitivity:

h~10-16

• Coincidence analysis• Tens of sightings claimed in one year

• Claims questioned and eventually disproved• Hawking and Gibbons: energy innovation theory• Giffard: bar quantum limit

New generation cryogenic and ultra-cryogenic bars

EXPLORER detector at CERN (ROG)

NAUTILUS, Frascati

Dilution refrigerator: 50 mK

Resonant transducer

h ~ 5x10-19

Resonant motion sensor

Principle:

Resonant energy transfer to & fro

Mecahnical amplification

Beat spectrum:

Bar detector sensitivity

Maximum bandwidth: 20Hzm

M

NAUTILUS, 1999

IGEC(International Gravitational Event Collaboration)

Essential results:

• No impulse signals above 4x10-18

• Negligible false alarm when n>3 (<1/104 years)

Various controversial,single detector claimsavailable…

Remarkable… but insufficient

MiniGrail, Leiden

Interferometric detector working principle

1kHz 150km!!!f L

02 sin ,2

hL

c

interf

Resonance condition:2

LGW

Interferometric detector design

Fabry-Pérot arms: GW 150km

Photodiode: dark fringe:

• Photon flux waste

• Shot noise important

Light recycling technique:

• Power recycling

• Signal recycling

Delay lines

Details of VIRGO

Cascina site, near Pisa

Details of VIRGO

Vacuum pipe

Highly reflecting mirror

Summary status of LIGO

Nov. 1999: Official inauguration

Feb. 2002: Engineering run E7, 6 months

Sep. 2002: Science run S1, 17 days, + TAMA + GEO-600

Feb. 2003: Science run S2, 59 days,

Nov. 2003: Science run S3, 70 days, + TAMA + GEO-600

End of 2004: Science run S4: ~4 weeks

Spring 2005: Commissioning, ~6 months

Autumn 2005: Science run S5, ~6 months

After: Full observatory operation

LIGO Science run S3, and GEO-600

there are many GW sources at low frequencies

Earth-based detectors are seismic noise limited

If…

but…

then…

the solution is to go out to space

LISALISA

Brief chronology:

1993. Europe/US team submits LISA proposal as M3 project ofESA’s Horizon-2000 Science Programme.

1994. LISA is changed to cornerstone mission in ESA’sHorizon-2000 Plus, and approved as ESA alone.

1997. New studies to reduce cost: LISA is redefined as a three S/C Constellation, 1.4 ton payload.

NASA joins in (50% + 50%), launch advanced to ~2010.

1998. ESA’s FPAG recommends industrial study phase.

1999. System & Technology Study begins. Prime isDornier Satellitensysteme, LIST strongly involved.

2000. Final Report delivered to ESA.

2003. TRIP Review panel considers LISA medium risk.

2003. ESA’s 4th Nov SPC approves LISA, and LPF.

2004. NASA’s new exploration programme defers LISA to 2013.

LISA concept

Test masses

5 million km, 30 mHz

Transponder scheme

LISA sensitivity

Comparison with Earth detectors

2

1/ 2 21 -1/2( ) 4 10 1 Hz3 mHzh

fS f

4 110 Hz 10 Hzf

LISA’s assured sources

Cumulative Weekly S/N Ratios during Last Year Before MBH-MBH Coalescence

LISA orbit

Orbit dynamics

1o inclination0.01 eccentricity

The three spacecraft

Thermal shieldDownlink antennas

FEEP

Baffle

Solar panels

Supportstructures

Science module

Star tracker

The science module

LISA mission summary

Detection of GWs, sensitivity: 4x10-21 at 1 mHz

Payload:

Objective:

Six capacitive inertial sensorsSix set of four FEEP per S/CTwo lasers per S/C: ND-YAG, 1064 nm, 1 W

Six test masses of Au-Pt alloy, 40 mm a side, in three S/C

Fabry-Perot cavities, stability 30 Hz/sqrt(Hz), transpondersQuadrant photodiode detectors, fringe resol: 54 10 / Hz30 cm Cassegrain telescopes

Orbit: 1 AU, 0.01 ecc, 1 deg ecliptic inclin, 20 deg behind Earth

Launcher: NASA’s Delta, launch date: 2013

Spacecraft: Total mass: 1380 kgTotal power: 940 W/compositePointing performance: few n-rad/sqrt(Hz) in bandScience data rate: 672 bps each S/C

Telemetry: 7 kps, 9 hour/2 days; Deep Space Network

LISA PathFinder (formerly SMART-2)

LISA’s requirements are extremely demanding.

Drag free subsystem can not be fully tested on Earth.

A previous, smaller technology mission, will assess feasibility:

LPFLPF

It will carry on board the LTP.

However it will be in a smaller scale, both in size and sensitivity.

Essentially, LTP will check:

• drag free technology• picometre interferometry• other important subsystems and software

LPFLPF

LPF Funding Agencies and countries

Mission:

DLR

SSO

Payload:

Prime contractor:– Platform: Astrium UK– Payload: Astrium Friedrichshafen

LTP concept

1. One LISA arm is squeezed to 30 centimetres:

2

1/ 2 14 -1/22

( ) 3 10 1 Hz ,3 mHza

f mS

s

1 mHz 30 mHzf

2. Relax sensitivity by one order of magnitude, also in band:

30 cm

LTP Objectives :

• Drag-free• Interferometry• Other…

LTP functional architecture

Ground SupportEquipment

(GSE)

LTP flightdynamicssimulator

Integration GSE

IS GSE

Optical metrologyGSE

LPF orbit

• Lagrange L1

• Launch: Sep-2008

• Travel time:

3 months

• Mission lifetime:

100 days LTP

100 days DRS

• Launch vehicle: Rockot

from Plesetsk

LTP functional architecture

Inertial sensors(IS)

Chargemanagement

system

IS core

CagingMechanism

IS Front EndElectronics

Drag-free subsystem

For LISA to work test masses must be (nominally) in free fall.

But there are perturbations which tend to spoil this:

External agents, e.g., solar pressure, magnetic fields…

Internal disturbances, caused by instrumentation itself

To compensate for these, a drag-free system is implemented.

It has two fundamental components:

A position sensor An actuation system

Drag-free working concept

Courtesy of S. Vitale

Drag-free working concept

Courtesy of S. Vitale

Drag-free working concept

Courtesy of S. Vitale

Drag-free working concept

Courtesy of S. Vitale

Drag-free working concept

Courtesy of S. Vitale

Drag-free working concept

Courtesy of S. Vitale

Drag-free working concept

Courtesy of S. Vitale

Drag-free working concept

Courtesy of S. Vitale

Drag-free working concept

Courtesy of S. Vitale

Capacitive position sensing principle

Bias: few volts at 100 kHz

Nanometre precision comfortably attained

outs

out 1 2 d dp

( ) ( ) ( ) sin (2 )N

V t C C V tV t f tN

x

Rotational and translational control example

Inertial sensor structure

LTP functional architecture

Optical MetrologyUnit (OMU)

Optical MetrologyFront EndElectronics

Laser Unit

Optical Bench

Acousto-opticmodulator

Laser

LTP optical metrology

To interferometer:Mach-Zenderheterodyne

Power = 1 mW = 1.064 m

hetcos c( )

( os 2)l

ft

t t

Signal:

1 2,f f few MHz

het 1 2f f f 1kHz

LTP interferometer

Reference

x1-x2 x1

Frequency

Readout: quadrant InGaAs photodiodesA

C D

B

The LTP EM optical bench

The LTP EM OB: after-shake tests: phase

LTP functional architecture

LTP structure(LTPS)

Structure

Gravitationalbalance system

Thermal Shield

The LTP structure

ASD, courtesy of S. Vitale

The LTP structure

ASD, courtesy of S. Vitale

The LTP structure

ASD, courtesy of S. Vitale

The LTP structure

ASD, courtesy of S. Vitale

The LTP structure

ASD, courtesy of S. Vitale

The LTP structure

ASD, courtesy of S. Vitale

The science spacecraft

• The science spacecraft carries the the LTP and DRS, the micro-propulsion systems and the drag free control system. Total mass about 470kg

• Inertial sensor core assemblies mounted in a dedicated compartment within the central cylinder.

• DRS Colloid thrusters mounted on opposing outer panels.

• Payload electronics and spacecraft units accommodated as far away as possible from the sensors to minimise gravitational, thermal and magnetic disturbances.

• FEEP and cold-gas micro-propulsion assemblies arranged to provide full control in all axes.

Courtesy of G. Racca

LTP functional architecture

Diagnostics andData

Management Unit(DMU)

Diagnostics enditems

DMU anddiagnostics box

DDS: Data Management & Diagnostics Subsystem

Diagnostics items:

• Purpose:– Noise split up

• Sensors for:– Temperature– Magnetic fields– Charged particles

• Calibration:– Heaters– Induction coils

DMU:

• Purpose:– LTP computer

• Hardware:

– Data Processing Unit (DPU)– Power Distribution Unit (PDU)– Data Acquisition Unit (DAU)

• Software:

– Process phase-meter readout– Charge management control– UV light control– Caging mechanism drive (TBC)– DFACS split (?)

Noise analysis concept

2 2

2 2

d x d ha L

dt dt

F

m

2 2a x Lm

hF

1/ 21/ 2

2

( )( ) ,F

h

SS

mL

equivalent signal

2

1/ 2 22

1 -4 1/( ) 1 Hz ,3 mH

3 10za

f mS

s

1 mHz 30 mHzf

Test mass equation of motion (1 dimension):

In frequency domain:

Thus spurious forces fake GW signals, with spectral density:

LTP top level science requirement rephrased:

S / C

S C2intnoise p n 2

fb

x S/ C TMrelative displacement

Ffa x

m M

Noise apportioning

Direct forces on test mass:

Thermal gradients Magnetic forces Fake interferometer noise

Coupling to S/C:

Test mass position fluctuations Drag free response delay Charged particle showers

Diagnostics items

Noise reduction philosophy

Problem: to assess the contribution of a given perturbation to the noise force fint.

Approach: 1) Apply controlled perturbation to the system

2) Measure “feed-through” coefficient between force and perturbation:

int( )f

F

3) Measure actual with suitable sensors

4) Estimate contribution of by linear interpolation:

int ( ) ( )f F

5) Substract out from total detected noise:

red int int ( )f f f

6) Iterate process for all identified perturbations

Example

Courtesy of S. Vitale

Various diagnostics items

Temperature and temperature gradients:– Sensors: thermometers at suitable locations– Control: heaters at suitable locations

Magnetic fields and magnetic field gradients:– Sensors: magnetometers at suitable locations– Control: induction coils at suitable locations

Charged particle showers (protons):– Sensors: radiation monitor (Mona Lisa)– Control: non-existent

Direct forces

Coupled to S/C

Specifications follow from mission top level requirements

Diagnostics science requirements

Ref. num 

LISA LTP

Req. 107 Temperature PSD (optical bench) 10-4 K/Hz 10-4 K/Hz

Req. 108 Temperature difference PSD (IS) 10-5 K/Hz 10-4 K/Hz

Value

Magnetic Field T

T/m

Magnetic Field Fluctuation PSD 650 nT/Hz

25 (nT/m)/HzMagnetic Field Gradient PSD

Magnetic Field Gradient

Magnitude

Overflow for 108 p/cm2 Solar Energetic Proton (SEP, >100 MeV) at peak flux

BB

RMRM

DDS current development status

Thermal:

• NTC and RTD devices identified and procured (EM)• FEE designed and built (EM)• First round of tests and data analysis complete• New tests underway

Magnetic:

• Some preliminary studies and surveys• New team has recently assumed responsibility

Radiation monitor:

• Full conceptual design ready• Front-end Electronics Designed• Rest of components selected from ESA/NASA qualified parts• Some other parts to be defined

DMU:

• In situ design and manufacture (price)• Advanced state of development, redundancy requested• Software writing in progress

Long term:

– LISA is fully endorsed by FPAG and SSAC

– Full, first class participation in LISA:

Technology developments Science yield

– LISA PathFinder:

Fulfill accepted LTP/DDS commitments• MEC funds until 2007, 3.9 MEU• New projects needed until LPF launch in 2008

Create qualified Science and Technology teams Can Science already be done with LPF?

Short-medium term:

Conclusion and future prospects

End of presentationEnd of presentation

IGEC

Garching delay line prototype

Delta launcher

LPF operation orbit and injection

LPF operation orbit and injection

FEEP (Field Emission Electric Propulsion)

Cs or In ions

Range: 0.1 N < F < 100 N

Resolution: 0.1 N

Power: 50 mW/N

Negligible sloshing

Long life: 9 gr/thruster.2 yr

Low noise, no mechanical parts

LISA needs six sets of four thrusters per S/C for full drag free control

3 1/ 21.66 10 Newtone fF I U

The entire payload

Various launcher alternatives

Rockot Dnepr Ariane 5

The LTP optical bench

Thermal diagnostics: current status

Sensor choice: NTC & RTD to be tested

PIC C

HP34402A

IEEE-488

USB

RS232

USB

FE

E

Al blockFOAM

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

MUX, GAIN control

16 bit data

NTC type sensor

RTD type sensor

Reference resistor.Vishay S102J 10k

Test setup only. Not part of DMU-LTP

LabVIEW

NTC2

NTC1

NTC1

NTC2

NTC2

NTC3

NTC3

NTC2

NTC2

RTD1

RTD1

RTD2

RTD2

NTC3

NTC2

RTD2

Test Philosophy

Thermal diagnostics: current status

Thermal diagnostics: clean room at NTE

Thermal diagnostics: foaming process

Thermal diagnostics: sensor inserts

Thermal diagnostics: first NTC results

• Magnetometer top level requirements from LTP magnetic requirements (TBC).

Magnetic Field 10 μT

Magnetic Field Gradient

5 μT

Magnetic Field PSD 650 nT

Magnetic Field Gradient PSD

25 nT

Sample rate: 0.33 sample/second (x 3 components)

Bits/sample: 16

Range: variable (± 10 μT, ± 30 μT ± 100 μT)

Resolution (FS/216) variable (0.305 nT, 0.91 nT, 3.05 nT)

Noise (for SNR=10 dB in ± 10 μT range) 40 pt / sqrt Hz @ 0.15Hz

Mass, power, drift.

• Survey of suitable magnetometer technologies. Candidate: Fluxgate Magnetometer.

Technology FGM AMRM GMRM HEM

Measurement Vectorial Vectorial Vectorial Vectorial

Range 1 pT – 1 T 100 pT- 1 T 100 pT- 1 T 1uT- 100 T

Precision(noise) 5-10 pT/√Hz @ 1 Hz 3-10 nT/√Hz @ 1 Hz 20 pT/√Hz @ 100 Hz 10 nT/√Hz @ 1Hz

Drift0.2 nT/yr

30-50 ppm/ºC

(temp)

600 ppm/ºC

(temp)

600 ppm/ºC

(temp)

600 ppm/ºC

Power Consumption <0.5W <0.5W <0.5W <0.5W

Magnetic diagnostics

Magnetic diagnostics

Helmholtz coil configurations analysed:

Preliminary magnetometer survey: flux-gate, Hall effect,…

Radiation monitor

18 x 18 mm2

10 x 10 mm2

10 mm

Telescopic Configuration reduces the Angular acceptance on particles and gives a better spectral resolution.

ChargeAmplifier

Pulse Shaper

DiscriminatorPeak

Holder ADC

Control Logic

ChargeAmplifier

Pulse Shaper

Discriminator

Rear Detector

B1

B2

B3

B4

B5

B6

B7 B8

B9

HV

Counter

Front Detector

Counter

INTERFACE

LOGIC

HV

DMU

Test PulseGenerator

VoltageReference

B10

B11

B12

HV Conv.

+12V

-5V Reg.

-12V +5V GND

DMU

Analog Front End DMUInterface

PowerControl

B13

B14 B15

B16

D1

D2

Radiation Monitor

Data Control & Analysis

Analoge Block

Power Block

IS FEE PCUIsolated DC/DC

Auxiliary PowerSupply

Isolated DC/DC

EMIFilter

EMIFilter

+28V-1

+28V-2

+5V +/-12V +/-48V

Processor Block

Shieldedamplifiers

Hardwire commands

RS-422 to S/C

4xRS-422 to PhasemeterD

AT

A B

US

PO

WE

R B

US

Drivers

Temp. sensors

Heaters & Coils

Magnetometer

DMU Block Diagram

DMU mechanical design

Box Cover

Analog Box

Procesor BoxPower Box

CoverBlackplane

220290

95

162.5

DMU mechanical design

Structural Ears

PCB

Frontal Connectors

Rear Connectors

Frame