English: In this photograph, the Hubble Space Telescope (HST) is clearing the cargo bay during its deployment on April 25, 1990. The photograph was taken by the IMAX Cargo Bay Camera (ICBC) mounted in a container on the port side of the Space Shuttle orbiter Discovery STS-31 mission. The purpose of the HST, the most complex and sensitive optical telescope ever made, is to study the cosmos from a low-Earth orbit for 15 years or more. The HST provides fine detail imaging, produces ultraviolet images and spectra, and detects very faint objects. Two months after its deployment in space, scientists detected a 2-micron spherical aberration in the primary mirror of the HST that affected the telescope's ability to focus faint light sources into a precise point. This imperfection was very slight, one-fiftieth of the width of a human hair. A scheduled Space servicing mission (STS-61) in 1993 permitted scientists to correct the problem. During four space walks, new instruments were installed into the HST that had optical corrections. A total of four HST servicing missions have taken place since its deployment: STS-61 in December 1993, STS-82 in February 1997, STS-103 in December 1999, and STS-109 in March 2002. The Marshall Space Flight Center had responsibility for design, development, and construction of the HST. The Perkin-Elmer Corporation, in Danbury, Cornecticut, developed the optical system and guidance sensors.