NASA’s Hubble Space Telescope is the first space-based observatory specifically designed for servicing by astronauts while in orbit. The ability to make repairs and upgrade Hubble’s instruments while in orbit became even more important when in 1990, shortly after deployment, NASA discovered that the observatory's primary mirror had an aberration that affected the clarity of the telescope's early images. Astronauts corrected that aberration on their first servicing mission in December 1993. Some 30 years later, Hubble continues to capture our imaginations with its stunning imagery.  

Hubble servicing missions involved intensive coordination between NASA's Kennedy Space Center in Florida, Johnson Space Center in Texas, and Goddard Space Flight Center in Maryland. Preparations included astronaut training at all three centers; simulations of shuttle and telescope operations during the mission at Johnson and the Space Telescope Operations Control Center (STOCC) at Goddard; testing and preparing instruments and hardware for flight at Goddard; and preparing launch operations and the space shuttle for launch, flight, and landing at Kennedy.

During the missions, operations took place primarily at Johnson and in Goddard's STOCC. Johnson’s Mission Control Center monitored every aspect of the space shuttle and astronauts, including spacewalks, procedures and schedules, crew activities and health, and in-cabin and cargo bay systems and experiments. The STOCC ground crew handled telescope operations, sending commands to Hubble to place the instruments into "safe hold" (hibernation) or turning them off and on as needed, close the aperture door (which covers the precious optical components), and perform maneuvers to position the telescope for grappling by the shuttle’s robotic arm, operated by astronauts to bring Hubble into the shuttle’s payload bay.

After the repair of existing instruments, installation of new instruments, and replacement of critical hardware, or science instruments, STOCC personnel performed tests to make sure each component had power and operated as it should. Many of these tests occurred during the astronauts' sleep cycles, when the STOCC team carried out detailed tests on the newly installed components to determine whether the astronauts needed to perform additional service. 

Once the astronauts completed all of the servicing tasks via a three- to five-day series of spacewalks, the STOCC controllers and Johnson Mission Control prepared the telescope for release. Often this also involved using the shuttle’s thrusters to carry Hubble into a slightly higher orbit, a step that prolonged Hubble's life by keeping it from naturally deorbiting due to atmospheric drag. 

The astronaut crew used the shuttle’s robotic arm to slowly raise Hubble from the payload bay and out into space, where controllers at the STOCC  opened  Hubble's  aperture door and made sure the telescope was functioning normally on its own. Returning Hubble to full science observations after a servicing mission usually took a few months.