Figure: House Call: Discovery on Its Way to Hubble

The Space Shuttle Discovery takes off on a mission to upgrade and repair Hubble in 1999. Once it gets close enough to Hubble, the shuttle uses its robotic arm to tow the telescope into its cargo bay for astronauts to work on. Astronauts routinely visit Hubble to perform maintenance work and install new instruments, thanks to the telescope's unique construction with replaceable parts.

Credit: NASA

http://hubblesite.org/gallery/spacecraft/17/