A mock-up of the Hubble Space Telescope in an enormous tank of water. An astronaut, standing on a replica of the Space Shuttle's robotic Canadarm is practicing the installation of Hubble's Science Instrument Command and Data Handling Module. On the far left, a scuba diver works on another component.

Hubble’s Science Instrument Command and Data Handling Module

An astronaut is training on how to install Hubble's Science Instrument Command and Data Handling Module prior to Servicing Mission 4.

Credits: NASA