n 2003, the Hubble Space Telescope took the image of a millenium, an image that shows our place in the universe. Anyone who understands what this image represents, is forever changed by it.
The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. Its position outside the Earth's atmosphere provides significant advantages over ground-based telescopes — images are not blurred by the atmosphere, there is no background from light scattered by the air, and the Hubble can observe ultra-violet light that is normally absorbed by the ozone layer in observations made from Earth. Since its launch in 1990, it has become one of the most important instruments in the history of astronomy. With it, astronomers have made many observations leading to breakthroughs in astrophysics. Hubble's Ultra Deep Field is the most sensitive astronomical optical image ever taken.
From its original conception in 1946 until its launch, the project to build a space telescope was beset by delays and budget problems. Immediately after its 1990 launch, it was found that the main mirror suffered from spherical aberration due to faulty quality control during its manufacturing, which severely compromised the telescope's capabilities. However, after a servicing mission in 1993, the telescope was restored to its intended quality and became a vital research tool as well as a public relations boon for astronomy. The HST is part of NASA's Great Observatories series, with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. Hubble is a collaboration between NASA and the European Space Agency.
The Hubble is the only telescope ever designed to be serviced from space by astronauts. To date, there have been four servicing missions, with a fifth and final mission planned for September 2008. Servicing Mission 1 took place in December 1993 when Hubble's imaging flaw was corrected. Servicing Mission 2 occurred in February 1997 when two new instruments were installed. Servicing Mission 3 was split into two distinct missions: SM3A occurred in December 1999 when urgently needed repairs were made to Hubble; and then SM3B followed in March 2002 when the Advanced Camera for Surveys (ACS) was installed.
Since SM3B, the Hubble has lost use of two major science instruments and is operating with viewing restrictions because of rate-sensing gyroscope failures. There are six gyroscopes onboard Hubble and three are normally used for observing. However, after further failures, and in order to conserve lifetime, a decision was taken in August 2005 to switch off one of the functioning gyroscopes and operate Hubble using only 2 gyros in combination with the Fine Guidance Sensors. This mode retains the excellent image quality of Hubble, and provides a redundancy should it be needed. Further redundancy is available now that an operational mode requiring only one gyro has now been developed and tested. Six new gyroscopes are planned to be installed in SM4.