Fine guidance sensor

A fine guidance sensor (FGS) is an instrument on board a space telescope that provides high-precision pointing information as input to the telescope's attitude control systems. Interferometric FGSs have been deployed on the Hubble Space Telescope; a different technical approach is used for the James Webb Space Telescope's FGSs. In some specialized cases, such as astrometry, FGSs can also be used as scientific instruments.