Focal is a facility designed to perform optical tests on payloads in a thermal vacuum space environment. The vacuum chamber is a vessel of horizontal cylindrical shape having 5 m (16.4 ft) diameter and 6 m (19.7 ft) length. The vacuum limit is about 1 nbar. Inside the vessel an optical table ensures a stability better than 10 μg. A thermal environment is simulated by shrouds specific to each experiment. The thermal facilities allow the feeding and control of 10 independent shrouds at 10 different temperatures between 170K (-153°F) and 370K (206°F) with a stability of 0.1 K (0.18°F). This facility has been used for the thermal vacuum and thermal balance tests of the ESA Hipparcos astrometry payload.