HST SM4 COS Installation EVA Removal Wide Shot

Cosmic Origins Spectrograph (COS) will be the most sensitive ultraviolet spectrograph ever flown on Hubble. COS will probe the "cosmic web" - the large-scale structure of the universe whose form is determined by the gravity of dark matter and is traced by galaxies and intergalactic gas. COS will explore how the "cosmic web" evolved from ancient times. COS will also sample the chemical content and physical state of gas in distant galaxy halos, providing important insight into the building process of early galaxies and the production of elements heavier than hydrogen and helium over cosmic time. Required to accomplish these goals is the extraordinary sensitivity of COS's far-ultraviolet channel—a factor more than 30 times greater than that of previous spectroscopic instruments for the detection of extremely low light levels. A two-fold enhancement will be offered by COS's near-ultraviolet channel. To install the COS instrument into the Hubble Space Telescope, he Servicing Mission 4 astronauts will remove the Corrective Optics Space Telescope Axial Replacement (COSTAR) instrument (installed during Servicing Mission 1 in 1993, to correct for Hubble's spherical aberration) and then install COS in its place.