1. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Introduction and context  Fundamental physics and geophysics in space share common constraints and technologies, e.g. : Long term acquisitions for detecting low frequency, low amplitude phenomena (fractions of second to hours) Precise understanding of the gravity (test of the theory of gravity, gravity field perturbations due to geologic effects)  Two ‘instrumental’ problems are addressed in this WP : How to improve the sensitivity of the present planetary seismometers ? What are the limiting noises of the next generation of drag-free satellites ?  Two on-going studies at the interface between fundamental physics and geophysics in space : Development of an interferometric read-out system for planetary seismometers System simulation and noise characterization of the LISA Pathfinder drag-free mission

2. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Objectives  Optical readout Use of interferometric techniques (Fabry-Perot cavity) to measure the displacement of the seismometer arm. Noise frequency bandwidth : 10 -2 to 10 Hz Current capacitive techniques seem to have reached their limit at about 10 pm/√Hz displacement noise Theoretically, optical techniques can improve this performance by 1 to 2 orders of magnitude The design should be compatible with space-based operations (c ompactness, robustness, low power consumption, etc.)  Simulations and analyses of LISA Pathfinder data Understanding of the limiting noises In-flight characterization of µ-Newton (cold gas) thrusters Improvement of the LPF simulator (State Space Model) Pave the way for an eLISA simulator

3. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Main results on the LISA Pathfinder analysis  Work performed by Henri Inchauspé (PhD)  A technical simulator for eLISA based on the LPF experience State Space Model (as for LISA Pathfinder) developed under MATLAB Simplified model with 1 test mass (TM) / spacecraft (SC) TM 1 TM2TM2 TM 3 TM5 TM4TM 6 CoM 3-6 O 12 (T) x y CoM 12 CoM 34 CoM 56 X : State vector M : Mass matrix A : State matrix B : Input (torques) matrix

4. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Main results on the LISA Pathfinder analysis  Test case : computation of the S/C drift w.r.t the TM due to the gravity gradient within the S/C on pure Keplerian orbits Expected drift of ~3m over 1 year  Comparison between analytical model and SSM : error <10 µm after 1 year  On-going work on a Drag Free and Attitude Control System (DFACS) for eLISA, objectives : Keep the TM within its cage Guarantees the laser pointing from one S/C to the others.

5. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Main results on the LISA Pathfinder analysis  Study of cold gas thrusters On-going implementation of (approximate) analytical state space equations into the SSM of LISA Pathfinder  Participation to LPF mock data challenges Realistic simulations provided by ESA and analyzed by scientists to retrieve the system characteristics (use of the SSM simulator …) In the same conditions as for the mission

6. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Main results on the seismometer development  Work performed by John Nelson (postdoc)  Global design of the experiment  Provision of the laser source, fiber components and photodiodes  Development of a force balance  First cavity proto- type being mounted

7. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space

8. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Main results on the seismometer development  In-depth study of the thermal noise sources for the cavity The dominant noises are from spacer and mirrors (incl. coating) brownian noise. Thermal noise level is theoretically compatible with 10 -15 m/√Hz at 10 mHz  Influence of the tilt misalignment (seismometer arm movement) on the coupling into the fiber Simulated … and found to be negligible …

9. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Main results on the seismometer development  Optimization of the cavity geometry and sensitivity to vibrations Mirror focal length optimization Optimization of support points First (quick and dirty…) simulations of cavity deformations due to vibrations – ~10 µm max deflection under 1g but almost no bending (hence no tilt), nor cavity length changes

10. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Project objectives for 2014 – 2015  LISA Pathfinder analyses Improvement of the LPF SSM simulator, knowledge transfer towards a SSM simulator for eLISA Tests procedures for characterizing the µNewton cold gas thrusters (especially their noise levels) Model updates based on the final AIVT of the satellite – LPF is planned for launch in July 2015 Participation to the inflight commissioning during the cruise of LPF to its final position (2 nd semester 2015)  Optical readout for seismometer Manufacturing of the Invar prototype and first tests Determination of the sensitivity to vibrations and thermal perturbations (with a fixed arm) New cavity design (if needed) for mounting on the force balance Comparison to existing capacitive readout systems Duplication and characterization Design constraints for implementation in a space-based VLB seismometer

11. Hubert HalloinScientific Committee 2013 WP Interface I3(APC/IPGP) : Fundamental Physics and Geophysics in Space Relevance to the LabEx themes  LISA Pathfinder analyses Immediate need for the mission, contribution of the LabEx to a fundamental physics project (GW detection) Prepare collaborations and expertise for future drag-free missions, e.g. in planetary sciences  Optical readout for seismometers R&D for the next generation of seismometer, potential technological breakthrough Technological interface between fundamental physics and planetary missions : new technical approach and development of tests beds with similar constraints (low freq. perturbations) Leverage effects  Interdisciplinary University grant awarded in 2012 : 20 k€ purchase of the main optical equipment for starting the experiment