ACS - Advanced Camera for Surveys - The Advanced Camera for Surveys (ACS) is a third-generation imaging camera. This camera is optimized to perform surveys or broad imaging campaigns. Currently only the Solar Blind Channel is available for science observations. The Wide Field and High Resolution Channels are not functioning. Astronauts will attempt to repair ACS during Servicing Mission 4 to the telescope.
COSTAR - Corrective Optics Space Telescope Axial Replacement - Second-generation corrective optics. COSTAR is not an actual instrument. It consists of mirrors which refocus the abbreviated light from Hubble's optical system for first-generation instruments. COSTAR is no longer needed as all of the subsequent instruments have had the correction built in. COSTAR will be removed during SM4 to make room for the new Cosmic Origins Spectrograph (COS).
NICMOS - Near Infrared Camera/Multi-Object Spectrometer - Second-generation imager/spectrograph. NICMOS is Hubble's only near-infrared (NIR) instrument. To be sensitive in the NIR, NICMOS must operate at a very low temperature, requiring sophisticated coolers. Problems with the solid nitrogen refrigerant have necessitated the installation of the NICMOS Cryocooler (NCC) on SM3B to continue its operation. NASA may attempt to restart NICMOS after SM4.
STIS - Space Telescope Imaging Spectrograph- Second-generation imager/spectrograph. STIS is used to obtain high resolution spectra of resolved objects. STIS has the special ability to simultaneously obtain spectra from many different points along a target. STIS is currently not functioning. Astronauts will attempt to repair STIS during Servicing Mission 4 to the telescope.
WFPC2 - Wide Field Planetary Camera 2 - Second-generation imaging camera. WFPC2 is an upgraded version of WF/PC (1) which includes corrective optics and improved detectors. WFPC2 will be replaced with Wide Field Camera 3 (WFC3) during Servicing Mission 4.