The Hubble Space Telescope, the first major optical telescope ever hurled into space, broke down a lot. Since its launch in 1990, NASA has organized five separate missions to service the Hubble—and it was doable, even though the telescope is 300 miles away from Earth. In the final servicing mission in 2009, the Space Shuttle Atlantis carried four astronauts to the observatory for a 12-day mission, when they replaced old batteries and equipment, while adding two new instruments to expand the capabilities of the Hubble, which is still going strong.

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