The ACS was installed on Hubble by the crew of the Space Shuttle Columbia (STS-109) during its Servicing Mission 3B on March 7, 2002. The ACS replaced the Faint Object Camera  (FOC), which was designed as two camera systems to independently view very-faint ultraviolet (UV) light from 115 to 650 nanometers (115 to 6,500 angstroms) in wavelength (where one nanometer equals one-billionth of one meter and ten angstroms).

The FOC was one of five original scientific instruments aboard Hubble when it was launched into orbit about the Earth aboard the Space Shuttle Discovery (STS-31) on April 24, 1990. The other four original Hubble instruments are: the Wide Field and Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), and Faint Object Spectrograph (FOS).

The Servicing Mission 1 crew aboard the Space Shuttle Endeavour (STS-61) in December 1993 replaced the HSP with the Corrective Optics Space Telescope Axial Replacement (COSTAR) package and replaced the WF/PC with the Wide Field and Planetary Camera 2 (WF/PC2).

The Servicing Mission 2 crew aboard the Space Shuttle Discovery (STS-82) in February 1997 replaced the GHRS with the Space Telescope Imaging Spectrograph (STIS) and replaced the FOS with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

The ACS was designed by scientists at The Johns Hopkins University to take optical images of large sections of the sky. It is the primary imaging instrument aboard Hubble because of its ability to provide very sensitive and wide-ranging views—ranging from the Earth’s solar system to the most distant objects in the universe. The ACS observes celestial bodies with three electronic cameras along with filters and dispersers that independently observe between the ultraviolet and near-infrared regions of the electromagnetic spectrum: 115 to 1,100 nanometers (1,150 to 11,000 angstroms). The solar blind camera (SBC) covers from 1,150 to 1,700 angstroms, the high resolution camera (HRC) covers 2,000 to 11,000 angstroms, and the wide field camera (WFC) covers between 3,700 and 11,000 angstroms.

The January 27, 2007 failure of the ACS was not its first. ACT went down in June 2006 due to an electronic failure but returned to normal operations on July 4, 2006. Again, on September 29, 2006, the ACS failed due to another electronic failure, but it again was able to resume normal observations. However, NASA scientists are not so confident this time that ACS will be able to continue with its mission. They are hopeful that partial resumption of operations with the SBC camera will occur sometime in February 2007.

If ACS is not able to resume normal operations, it may not be repaired during the upcoming Servicing Mission 4 by NASA’s space shuttle Atlantis (STS-125) tentatively scheduled for September 11, 2008. Preston Burch, Hubble associate director at NASA’s Goddard Space Flight Center, has initially indicated that the mission is already too busy and complicated to add another spacewalk to repair the ACS. In addition, much more effort would be needed to reach the ACS, which is positioned in an area difficult to reach by space-walking, Hubble-repairing astronauts.

Obviously, in the meantime, Hubble ground personnel will be working to restore function to the ACS. Only time will tell if ACS comes back online.

The ACS Web site from The Johns Hopkins University is located at: http://acs.pha.jhu.edu/.

The ACS Web site from the Space Telescope Science Institute is found at: http://www.stsci.edu/hst/acs.

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