Servicing Mission 1
In the early plans for telescope operations, maintenance visits were planned for every 2.5 years and that every five years HST would be transported back to the ground for a larger overhaul. This plan has changed somewhat over time and a servicing scheme, which includes Space Shuttle Servicing Missions (SM) every three years, but no returns to Earth has been decided upon.
In the first three years of operations HST did not meet expectations because its primary mirror is 2 microns too flat at the edge. The first Servicing Mission in December 1993 (STS-61 - on which the European astronaut Claude Nicollier flew) corrected for this problem by installing a new instrument with corrective optics (COSTAR - Corrective Optics Space Telescope Axial Replacement). With this pair of "glasses" HST's golden age began. The images were as sharp as originally hoped for, and new, astonishing results started to emerge on a regular basis.
The High Speed Photometer (HSP) instrument was replaced by COSTAR and the older Wide Field Planetary Camera (WFPC) was replaced with a newer version (WFPC2). The malfunctioning solar arrays were also replaced.