NASA selected the Cosmic Origins Spectrograph (COS) as a 4th generation replacement instrument for the Hubble Space Telescope (HST) Servicing Mission 4 now scheduled for early 2004. COS will go into the bay currently occupied by COSTAR, which, now that the Advanced Camera for Surveys (ACS) has been installed in place of the FOC, will no longer be used. Joining COS on the SM4 flight is the Wide Field Camera 3, which will replace WFPC2. COS will complement and extend the suite of scientific instruments aboard HST, that will include COS, ACS, STIS, NICMOS, and WFC3 at the focal plane for the period 2004 until 2010 (the projected end of the HST mission).
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 and 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.
