Which instrument replaced the Faint Object Camera on Hubble?

The Advanced Camera for Surveys replaced Hubble’s Faint Object Camera. Astronauts installed ACS during Servicing Mission 3B, flown by Space Shuttle Columbia in March 2002, making the FOC the last of Hubble’s original science instruments to be removed.

ACS was designed primarily for wide-field surveys across ultraviolet and visible wavelengths. Its broad field of view and efficient detectors made it especially useful for imaging large numbers of galaxies, star clusters, and distant objects. NASA described its discovery power as roughly ten times greater than that of the camera it replaced.

The replacement also marked an important change in Hubble’s optical history. The FOC had required corrective optics because Hubble’s primary mirror had spherical aberration. Newer instruments such as ACS incorporated their own corrective optics, allowing the separate COSTAR correction package to become unnecessary.

ACS has three camera channels: the Wide Field Channel, High Resolution Channel, and Solar Blind Channel. It later contributed to major projects including the Hubble Ultra-Deep Field. Its most-used channels suffered a serious electronics failure in 2007, although astronauts restored the Wide Field Channel during Servicing Mission 4 in 2009.