Weighing more than a ton before fueling and more than twice that with its tanks full, MRO is one of the biggest ships ever hurled towards Mars. Part of the reason for the heft is the suite of instruments it carries, including the largest diameter telescopic camera ever sent to another planet; ground-penetrating radar able to look beneath the Martian surface; and a climate sounder, able to study the atmosphere in both visible and invisible spectra. The ship will also carry a new-generation navigational camera and communications system, to be field-tested for the first time.
The unusually sharp vision the imaging instruments will give the MRO, coupled with it's low, 190-mi. orbit — 20% closer than any of the other three spacecraft currently orbiting Mars — mean it will get the best look yet at Martian surface features, including possible shorelines left behind by vanished oceans or seas. The radar will also allow MRO to search the planet as a whole for minerals that form in the presence of water, and to determine where and how deeply subsurface ice may lie. Where there's ice and water, evidence of life — either extinct or ongoing — could also be found. While rovers like Spirit and Opportunity offer a thorough going-over of a few isolated regions, only a clear-eyed orbiter can provide a close look at the entire planet.
Should the liftoff take place as planned, it will be another 15 months before the spacecraft settles into its low, circular orbit around Mars. After that, it will have a full two years to conduct its surveillance work — a long life for a robot ship, and one that should return a rich trove of science.