13 Launched in April 1990 aboard
Discovery, Hubble’s 547-kilometre
(340-mile) altitude puts it well outside Earth’s atmosphere, higher than Shuttles usually operate. Only Discovery’s 1997 mission to boost the telescope’s orbit has gone higher.
Along with producing beautiful images of the universe it has accurately measured the distances to Cepheid variable stars, allowing a more accurate measurement of the expansion of the universe, which also allows a more accurate estimate of its age.