LISA Pathfinder is a mission of the European Space Agency (ESA), which will test the technology needed to develop future space-borne gravitational wave detectors. LISA stands for 'Laser Interferometer Space Antenna'. One day it is hoped that eLISA will observe gravitational waves in the quiet environment of space.
A preliminary mission, LISA Pathfinder, was launched on 3 December 2015 with the objective of demonstrating that key technologies for eLISA function well in the vicinity of the L1 Earth-Sun Lagrange point, a destination some 1.5 million km distant from Earth that will be reached early in 2016.
The core of the test package consists of two proof masses, each 2 kg. To help ESA verify that these proof masses are sufficiently non-magnetic, their d.c. volume magnetic susceptibility was measured in Sèvres in 2007 and again in 2012 using the BIPM susceptometer, shown below. For one set of measurements (a) the cubic proof mass sat on a copper plate; the measurements were also made using an aluminium plate (b). As expected, the plate material had no influence on the final results even though copper is diamagnetic and aluminium is paramagnetic. All six faces of the cube were examined.