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Fine guidance sensor
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<p>A fine guidance sensor (FGS) is an instrument on board a <a href="/facts/Space_telescope/BtI46sDX">space telescope</a> that provides high-precision pointing information as input to the telescope's <a href="/facts/Spacecraft_attitude_control/hE6aMu26">attitude control</a> systems. <a href="/facts/Interferometric/X3E1SsQT">Interferometric</a> FGSs have been deployed on the <a href="/facts/Hubble_Space_Telescope/NQeIf0vw">Hubble Space Telescope</a>; a different technical approach is used for the <a href="/facts/James_Webb_Space_Telescope/w4GAWnWX">James Webb Space Telescope</a>'s FGSs. In some specialized cases, such as <a href="/facts/Astrometry/9ycEEAvD">astrometry</a>, FGSs can also be used as scientific instruments. </p>