Fine Guidance Sensor (HST)

[8] The FGS were originally made by the optics company Perkin-Elmer, and as removable and repairable instruments it has been possible to refurbish them over the lifetime of the telescope.

[9] The astronaut crew performed an EVA (spacewalk) to service the FGS and other components on the telescope in Earth orbit.

[11] The smallest Kuiper belt object (KBO) yet detected at that time was discovered in 2009 by poring over data from the Hubble Space Telescope's fine guidance sensors.

[12] They detected a transit of an object against a distant star, which, based on the duration and amount of dimming, was calculated to be a KBO about 1,000 meters (3,200 ft) in diameter.

[12] It has been suggested that the Kepler observatory may be able to detect objects in the Oort cloud by their occultation of background stars,[13] and the Whipple proposal would also try to use this concept.