At its distant orbit, Webb is much too far from Earth to be reached by the space shuttle. Webb's science mission length is 5 years with a 10 year goal. To insure the 5 year mission, NASA has engineered the observatory so that all critical subsystems have a backup or will degrade gracefully with age. For instance, the Near Infrared Camera has two identical camera systems so that the optical quality can be maintained even if one fails.
Webb will also contain enough fuel for 10 years of maneuvers. As with Hubble, Chandra, and Spitzer, the Webb science and operations center has the ability to change the operations of the observatory to maximize its scientific potential as it ages.
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