How to test NISP instrument for EUCLID mission in laboratory

The ESA mission Euclid is designed to explore the dark side of the Universe. The NISP (Near Infrared Spectro-Photometer) is one of its two instruments operating in the near-IR spectral region (0.9-2 m), that will be fully integrated and tested at Laboratory d'Astrophysique de Marseille (LAM) under vacuum and thermal conditions. The test campaign will regroup functional tests, performance tests, calibration procedure validation and observations scenario test. One of the main objectives of the test campaign will be the measurement of the focus position of NISP with respect to the EUCLID object plane. To achieve these tests campaign, a global Ground Support Equipment (GSE) called the Verification Ground System (VGS) has to be developed. It will be a complex set of GSE integrated in ERIOS chamber made of: a telescope simulator to simulate the EUCLID telescope and to inject light into NISP, a thermal environment to be used for NISP thermal balance and verification, a sets of mechanical interfaces to align all the parts into ERIOS chamber, the NISP Electrical GSE (EGSE) to control the instrument during the test and a metrology system to measure the positions of the components during the test. We will present the preliminary design and concepts of the VGS and we will show the main difficulties we have to deal with: design of thermal environment at 80K with 4mK stability, the development of a metrology system in vacuum, knowledge of the focus position within 150um in cold, etc. The main objectives of the NISP test will be explained and how the VGS responds to the test requirement.