Past, present and future of Gravitational Wavedetection ScienceJ. Alberto Lobo, Bellaterra, 13-October-2004

Presentation summaryCurrent GW detection research status:Acoustic detectorsInterferometersLISALPF and the LTPThe Diagnostics and DMU subsystemsFuture prospects

Earth based GW detectors

Bar conceptIdea of an acoustic detector (bar) is to link masses with a spring:so thatand GW signal gets selectively amplified around frequency W.Strongdirectionality

Real bar detectors 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 limitNew generation cryogenic and ultra-cryogenic bars

EXPLORER detector at CERN (ROG)

Resonant transducerh ~ 5x10-19

Resonant motion sensorBeat spectrum:

Bar detector sensitivity

IGEC(International Gravitational Event Collaboration)Essential results: No impulse signals above 4x10-18 Negligible false alarm when n>3 (

MiniGrail, Leiden

Interferometric detector working principle

Interferometric detector designFabry-Prot arms:Photodiode: dark fringe: Photon flux waste Shot noise importantLight recycling technique: Power recycling Signal recyclingDelay lines

Details of VIRGOCascina site, near Pisa

Details of VIRGO

Summary status of LIGONov. 1999: Official inaugurationFeb. 2002: Engineering run E7, 6 monthsSep. 2002: Science run S1, 17 days, + TAMA + GEO-600Feb. 2003: Science run S2, 59 days,Nov. 2003: Science run S3, 70 days, + TAMA + GEO-600

End of 2004: Science run S4: ~4 weeksSpring 2005: Commissioning, ~6 monthsAutumn 2005: Science run S5, ~6 monthsAfter: Full observatory operation

LIGO Science run S3, and GEO-600

there are many GW sources at low frequenciesEarth-based detectors are seismic noise limitedthe solution is to go out to space

LISA

Brief chronology:

LISA conceptTest masses5 million km, 30 mHzTransponder scheme

LISA sensitivity

Comparison with Earth detectors

LISAs assured sources

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

LISA orbit

Orbit dynamics

The three spacecraftThermal shieldDownlink antennasFEEPBaffleSolar panels SupportstructuresScience moduleStar tracker

The science module

LISA mission summary

LISA PathFinder (formerly SMART-2)LPFIt 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

LPF

LPF Funding Agencies and countries

LTP concept1. One LISA arm is squeezed to 30 centimetres:2. Relax sensitivity by one order of magnitude, also in band:

LTP functional architecture

LPF orbit

LTP functional architecture

Drag-free subsystem

Drag-free working conceptCourtesy of S. Vitale

Drag-free working conceptCourtesy of S. Vitale

Drag-free working conceptCourtesy of S. Vitale

Drag-free working conceptCourtesy of S. Vitale

Drag-free working conceptCourtesy of S. Vitale

Drag-free working conceptCourtesy of S. Vitale

Drag-free working conceptCourtesy of S. Vitale

Drag-free working conceptCourtesy of S. Vitale

Drag-free working conceptCourtesy of S. Vitale

Capacitive position sensing principleBias: few volts at 100 kHzNanometre precision comfortably attained

Rotational and translational control example

Inertial sensor structure

LTP functional architecture

LTP optical metrologyPower = 1 mWl = 1.064 mmSignal:

LTP interferometerReadout: quadrant InGaAs photodiodes

The LTP EM optical bench

The LTP EM OB: after-shake tests: phase

LTP functional architecture

The LTP structureASD, courtesy of S. Vitale

The LTP structureASD, courtesy of S. Vitale

The LTP structureASD, courtesy of S. Vitale

The LTP structureASD, courtesy of S. Vitale

The LTP structureASD, courtesy of S. Vitale

The LTP structureASD, courtesy of S. Vitale

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

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

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 showersDiagnostics items

Noise reduction philosophyProblem: to assess the contribution of a given perturbation to the noise force fint.

ExampleCourtesy 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-existentSpecifications follow from mission top level requirements

Diagnostics science requirementsTBRM

DDS current development statusThermal:

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

Some preliminary studies and surveys New team has recently assumed responsibilityRadiation monitor:

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

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

Conclusion and future prospects

End of presentation

IGEC

Garching delay line prototype

Delta launcher

LPF operation orbit and injection

LPF operation orbit and injection

FEEP (Field Emission Electric Propulsion)LISA needs six sets of four thrusters per S/C for full drag free control

The entire payload

Various launcher alternativesRockotDneprAriane 5

The LTP optical bench

Thermal diagnostics: current status Sensor choice: NTC & RTD to be tested

Thermal diagnostics: current status16 bit dataNTC1RTD1RTD2RTD2NTC3NTC2RTD2Test Philosophy

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).Sample rate: 0.33 sample/second (x 3 components)Bits/sample: 16Range: variable ( 10 T, 30 T 100 T)Resolution (FS/216) variable (0.305 nT, 0.91 nT, 3.05 nT)Noise (for SNR=10 dB in 10 T range) 40 pt / sqrt Hz @ 0.15HzMass, power, drift.Survey of suitable magnetometer technologies. Candidate: Fluxgate Magnetometer.Magnetic diagnostics

Magnetic Field10 TMagnetic Field Gradient5 TMagnetic Field PSD650 nTMagnetic Field Gradient PSD25 nT

TechnologyFGMAMRMGMRMHEMMeasurementVectorialVectorialVectorialVectorialRange1 pT 1 T100 pT- 1 T100 pT- 1 T1uT- 100 TPrecision(noise)5-10 pT/Hz @ 1 Hz3-10 nT/Hz @ 1 Hz20 pT/Hz @ 100 Hz10 nT/Hz @ 1HzDrift0.2 nT/yr30-50 ppm/C(temp)600 ppm/C(temp)600 ppm/C(temp)600 ppm/CPower Consumption

Magnetic diagnosticsHelmholtz coil configurations analysed:Preliminary magnetometer survey: flux-gate, Hall effect,

Radiation monitor18 x 18 mm2 10 x 10 mm2 10 mmTelescopic Configuration reduces the Angular acceptance on particles and gives a better spectral resolution.

Radiation MonitorData Control & Analysis

DMU Block Diagram

DMU mechanical design

DMU mechanical design