Henri Inchauspé’s PhD Defense – From LISA pathfinder to eLISA: building of a dynamics simulator for the eLISA space mission

Henri Inchauspé was recruited in 2012 by the Labex on the Interface project “Fundamental physics and Geophysics in space“. His PhD defense will be held on Wednesday 25 November at 10 am at APC, in the François Arago Centre, in room 360.

Thesis title:

From LISA pathfinder to eLISA: building of a dynamics simulator for the eLISA space mission.


The gravitational Universe and the rise of an entirely new astronomy using gravitational waves have been selected by ESA as the scientific theme for the future large space mission L3 planned for 2030 decade. In that context, eLISA mission seems favored, and is besides preceded by the LISA Pathfinder mission, about to be launched (December 2nd), that aims to demonstrate the technology envisaged. Focused on an observation frequency band lower that the current ground detectors, which the new generations have just started (ore are about to start) the observation runs, eLISA mission would be able to observe compact binary objects, like supermassive or intermediate black holes, neutron stars, white dwarves, and eventually cosmological sources (cosmic strings, Universe phase transitions). The scientific output of this mission would be very wide, concerning at the same time fundamental physics, cosmology and astrophysics.

Detection principle requires to maintain four cubic test masses in free fall, contained in three different satellites, thus forming a triangular constellation in heliocentric orbit. Laser links will connect the spacecraft (S/C) the ones to the others, and the interferometer thus formed will be sensitive to tidal deformations caused by gravitational waves crossing the detector. Preventing the test masses as much as possible from any stray external forces is primordial, because any oscillating acceleration of the test mass would be undistinguishable from gravitational waves signals. Metrology and disturbance reduction systems, called LISA Technology Package (LTP), will be tested in space conditions with LISA Pathfinder mission. One of the main objectives is to demonstrate that we are able to maintain two free falling test masses in an environment such that the differential acceleration between the test masses is lower than 3.10 -14 m.s -2.Hz -1/2 at the frequency 1 mHz.

LISA Pathfinder will represent an essential source of informations for the design and the estimate of eLISA sensitivity. My PhD work comes in this context and is focused on the building of a simulator of the dynamics of the test masses and the S/C, that aims to assess system performances, in particular the acceleration noise that limits the detector sensitivity at low frequencies, from the properties of the various measurement and actuation modules involved in the system, about which LISA Pathfinder will provide the most representative characterization.