The Cosmic Origins Spectrograph (COS) is a 4th generation axial science instrument for the Hubble Space Telescope (HST). Spacewalking astronauts will install it on Servicing Mission 4 (SM4), now targeted for October 8, 2008. COS will restore spectroscopy to HST's scientific arsenal, and at the same time provide unique new capabilities that will take the telescope into exciting, uncharted waters.  Astronauts will install COS in Bay 4, where it will replace COSTAR.  COS will complement and extend HST's suite of scientific instruments, which will include COS, ACS, STIS, NICMOS, and WFC3.

COS is a high-throughput ultraviolet (UV) spectrograph that is optimized to observe faint point sources. COS will be, by a large factor, the most sensitive UV spectrograph ever flown aboard HST.  It will bring the diagnostic power of UV spectroscopy to bear on such fundamental issues as: the ionization and baryon content of the intergalactic medium; the origin of large-scale structure in the universe; the ages, dynamics, and chemical enrichment of galaxies; and stellar and planetary origins. These science programs require having the capability to obtain moderate resolution (R > 20,000) spectroscopic observations of faint UV sources, such as distant quasars.

COS has two channels: a Far-Ultraviolet channel that is sensitive in the 1150 - 1775 Å wavelength range and a Near-Ultraviolet channel that operates between 1750 - 3200 Å.