How to create space inside the VLTI: PIONIER 3D project

PIONIER is a four beams combiner instrument developed by the Astrophysics Laboratory of Grenoble (LAOG, now IPAG). This instrument arrived at the ESO Paranal Interferometer in 2010 as a visitor instrument and was supposed to be decommissioned with the arrival of the second generation instruments GRAVITY and MATISSE. However, the success of PIONIER induced the needs to keep it available for the scientific community inside the packed environment of the VLTI. This paper presents the technical solutions that were applied to place the instrument in mezzanine without impacting its performance and with the constraint of reducing its operational workload.