The first servicing mission took place in December, 1993. Below is a list of the most important events that took place during the mission:

• Astronauts removed the original Wide Field Planetary Camera and installed an updated model equipped with built-in corrective optics that compensate for the flaw in the telescope’s primary mirror. The replacement instrument, built at the Jet Propulsion Laboratory, is called the Wide Field Planetary Camera 2 (WFPC2).
• Astronauts removed the High Speed Photometer and replaced it with the Corrective Optics Space Telescope Axial Replacement (COSTAR), which includes an assembly of coin-sized mirrors that are polished to a special prescription to compensate for the telescope’s flawed primary mirror.

Other replaced components:

• Solar Array Panels — Wing-like structures that produce electricity to power the observatory.
• Solar Array Drive Electronics — Modular hardware that controls the position of the solar arrays.
• Magnetometer -- Device that measures the telescope’s orientation within Earth’s magnetic field to help in attitude control.
• DF-224 Flight Computer Coprocessor — Computer memory that improves backup and computational power.
• Two Rate Sensor Units — Part of the telescope’s pointing system.
• Two gyroscope Electronics Control Units (ECUs) — Dedicated electronics that process measurements taken by the rate sensor units.
• Fuses — Fuse plugs for the gyroscopes.
• GHRS Redundancy Kit — A wiring kit that provides power to one of the detectors on the Goddard High Resolution Spectrometer.

Find out more from HubbleSite:

• Read about Servicing Mission 1 in Team Hubble.
• Learn about Hubble's science instruments and spacecraft systems in Nuts & Bolts.