The Hubble High Fidelity Mechanical Simulator (HiFi).
It is a mechanical mock-up of the HST aft shroud. Hubble's scientific
instruments, guidance sensors, electrical harnesses, thermal blankets, and
electronics equipment are located in Hubble's aft shroud. The HiFi was built
to perform verification testing of scientific instruments to be installed in
Hubble and to provide for astronaut training.
The horizontal black rectangle toward the top of the HiFi is the location in
which the Wide
Field Camera 3 will be installed on the servicing mission. When we
visited, the WFC3 was being tested in the Space Environment Simulator.
Additional information, including an exploded view diagram of the HiFi and the
area of the HST it simulates, can be found in Clean
Assembly and Integration Techniques for the Hubble Space Telescope High
Fidelity Mechanical Simulator.