NASA had originally decided against the maintenance mission because of the risk involved and the pressures to complete International Space Station (ISS) construction by 2010, when the shuttle is to be retired. But US politicians and world astronomers fought successfully to keep alive the instrument that has expanded knowledge of space.

Among the most important work done on the telescope was the addition of a new camera. The Wide Field Planetary Camera 3 will allow astronomers to see deeper into space and to capture images across all three regions of the light spectrum - ultraviolet, visible and near infrared.

Another new instrument, known as the Cosmic Origins Spectrograph will break up light into its components and allow astronomers to study the large-scale structure and origins of the universe, including how galaxies, stars and planets formed and how elements developed.