I3 : Fundamental physics and Geophysics in space
Through the space projects they have been or are pursuing, IPGP and APC have acquired an expertise in precision measurements of distances, times and acceleration in astrophysics, fundamental physics in space, Planetary surface, Earth surface and ocean bottom, as well as a leading role in France in the coordination of missions closely associated to these techniques, e.g. French LISA office (LISA France) and the French Planetary seismometer, selected onboard the NASA/INSIGHT mission.
The techniques involved are necessarily associated with high technology and often extreme precision, requiring unprecedented levels of noise control (often in harsh conditions and measurements at very low frequency) and space-compliant instruments. These techniques represent the path to the future and developing them will allow progress not only in the understanding of the most fundamental aspects of our environment, whether it is the Earth, solar system planets or the Universe at large, but also in the technological prospects for forthcoming space missions. They are indeed closely related with cutting edge knowledge and technologies such as nanotechnologies, high precision distance measurements, solid state physics, etc.
The goal of this WP is to continue R&D efforts in these domains, in order:
- to explore new technologies in acceleration measurements (e.g. with optical or quantum devices, including cold atoms, high temperature superconducting squids and tunneling diodes in the displacement or gravity sensors head, satellite/satellite laser and radio ranging),
- furthermore reduce mass and integrate control electronics (e.g. with the development of Asics, hybrids and highly integrated 3D packaging),
- precisely understand the physics of extremely low thrust engine (e.g. surface and chemical effects of ion sources used for micro-newton thrusters)
- and highly improve insulating structure and packaging by controlling thermal transfers at the nanoscale (e.g. nano thermal coating and micro-design of thermal insulations).
Position Name Laboratory Grade & Employer WP leader HALLOIN Hubert APC MCF, Paris Diderot WP co-leader LOGNONNE Philippe IPGP PR, Paris Diderot WP co-leader PLAGNOL Eric APC DR, IN2P3 WP member INCHAUSPE Henri APC Post-Doc, LabEx WP member FAYON Lucille APC / IPGP PhD, Paris Diderot WP member DE RAUCOURT Sébastien IPGP Research Engineer, CNRS WP leader HALLOIN Hubert APC MCF, Paris Diderot
Two main activities were conducted in this project: the first one on the LISA Pathfinder and LISA missions, the second one on seismometers for planetary missions. These 2 activities are described hereafter. The work performed since the beginning of the LabEx program is described, with an emphasis on the results obtained this last year.
LISA Pathfinder cold gas thrusters and LISA dynamics modelling
Henri Inchauspé successfully defended his thesis in November 2015. Since then and until September 2016, he continued working on LISA Pathfinder and dynamics modeling as a postdoc. Henri started a second postdoc position on the MICROSCOPE mission at the ONERA in October 2016 and is presently applying for a position at the University of Florida in Gainesville, to work on LIGO and the LISA mission.
Summary of the thesis / postdoc at the APC (Thesis title : « A noise simulator for eLISA: Migrating LISA Pathfinder knowledge to the eLISA mission ») :
The LISA Pathfinder mission has been launched in December 2015 and until its decommissioning in July 2017 provided valuable information on the technology and performances that will be used for the future LISA mission. It is thus of a great importance to be able to migrate the knowledge acquired from LISA Pathfinder to this future mission, thus giving the physics community a tool to understand its performances and to suggest possible improvements. The LISA Technology Package (LTP), which is tested during the LISA Pathfinder mission, involves many subsystems as, for example, the micro-propulsion system, the interferometer readout or the controllers.
This work was presented in September 2017 in a joint workshop, organized by the CNES, between the LISA Pathfinder and Microscope teams on the specific topic of drag free performance for these two missions. Comparing the results from these two missions – which are using the same cold gas thrusters – allowed identifying a possible source for the extra lines of the LPF data, located in the regulation control of the gas flow fed to the nozzle. This possible explanation is currently under further investigation.
Optical readout for planetary seismometers and mechanical transfer function of VBB seismometers’ leveling system
Since the beginning of the project, an in-depth study of the design and foreseen limiting noise of the readout system has been done.The system is based on two Fabry-Perot cavities and the difference of locking frequencies is monitored to deduce the movement of the common mirror
Lucile Fayon arrived on this project in october 2014, as a PhD student. Actually, the presence of a parasitic optical cavity (due to parasitic reflections on optical elements) have been identified, preventing from isolating the ‘real’ cavity signal. A new setup is being tested, using another, better adapted, focusing lens.
Lucile is also working on the mechanical model of the VBB seismometers’ leveling system embarked on the InSight mission. The objective is to determine the Eigen modes of this structure to see which ones can affect the seismic measurements, and to study the sensitivity of the leveling procedure to some parameters, such as the stiffness of the Martian ground. .
During this last year, this numerical model has been finalized and compared to experimental data, obtained from qualification and flight models. These results were then implemented into the simulations of signals from the penetrator device (HP3 MOLE) onboard InSight. Based on these simulations, the work performed by Lucile demonstrated that the six accelerometers within the SEIS instrument will allow disentangling the rotation and translation movements of the leveling system and, therefore, measure the phase velocity of the subsurface Rayleigh waves.
After the end of the LISA Pathfinder mission, the final analysis is going to be released soon and the acquired experience (in part thanks to the LabEx funding) is being transferred to the LISA mission.
Concerning the development of the optical readout system, the main objective is now to complete the PhD thesis of L. Fayon with the tuning and locking of the laser frequency on the cavity. This will allow assessing the experimental noise of the system and the expected performance of a seismometer with such a readout system.
Armano, M. et al. , Beyond the Required LISA Free-Fall Performance: New LISA Pathfinder Results down to 20 μHz, Physical Review Letters (2018), vol. 120, pp. 061101
Armano, M. et al. , Capacitive sensing of test mass motion with nanometer precision over millimeter-wide sensing gaps for space-borne gravitational reference sensors, Physical Review Letters D (2017), vol. 96, pp. 062004
Armano et al. Charge-Induced Force Noise on Free-Falling Test Masses: Results from LISA Pathfinder. Physical review letters (2017) vol. 118 pp. 171101
Armano et al. Constraints on LISA Pathfinder’s self-gravity: design requirements, estimates and testing procedures. Classical and Quantum Gravity (2016) vol. 33 pp. 235015
Nofrarias et al. Optimal design of calibration signals in space-borne gravitational wave detectors. Physical Review D (2016) vol. 93 pp. 102004
Armano et al. Sub-Femto-g Free Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results. Physical Review Letters (2016) vol. 116 pp. 231101
Armano et al. A noise simulator for eLISA: Migrating LISA Pathfinder knowledge to the eLISA mission. Journal of Physics: Conference Series (2015) vol. 610 pp. 012036 [Main author : Henri Inchauspé]
Armano et al. A Strategy to Characterize the LISA-Pathfinder Cold Gas Thruster System. Journal of Physics: Conference Series (2015) vol. 610 pp. 012026
Inchauspe et Plagnol. Migrating LISAPathfinder noise results to the eLISA mission. 40th COSPAR Scientific Assembly. Held 2-10 August 2014 (2014) vol. 40
Without a written acknowledgment of the UnivEarthS Labex support:
Vitale et al. Data series subtraction with unknown and unmodeled background noise. Physical Review D (2014) vol. 90 pp. 042003