It's orbiting Mars, as part of the Mars Reconnaisance Orbiter (MRO). It contains the largest telescope ever put on a planetary spacecraft (20 inches) and the highest resolution camera ever put into a planetary spacecraft. Once in it's final orbit, it will have a resolution of one (1") foot per pixel.
http://skyandtelescope.com/news/article_1703_1.asp
http://hirise.lpl.arizona.edu/HiRISE...ml#components]