Hubble was designed to accommodate regular servicing and equipment upgrades while in orbit. Instruments and limited life items were designed as orbital replacement units.[104] Five servicing missions (SM 1, 2, 3A, 3B, and 4) were flown by NASA Space Shuttles, the first in December 1993 and the last in May 2009.

Servicing missions were delicate operations that began with maneuvering to intercept the telescope in orbit and carefully retrieving it with the shuttle's mechanical arm. The necessary work was then carried out in multiple tethered spacewalks over a period of four to five days. After a visual inspection of the telescope, astronauts conducted repairs, replaced failed or degraded components, upgraded equipment, and installed new instruments. Once work was completed, the telescope was redeployed, typically after boosting to a higher orbit to address the orbital decay caused by atmospheric drag.

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