Launch: December 11, 1998
Mars Climate Orbiter was designed to function as an interplanetary weather satellite and a communications relay for Mars Polar Lander. The orbiter carried two science instruments: a copy of an atmospheric sounder on the Mars Observer spacecraft lost in 1993, and a new, lightweight color imager combining wide- and medium-angle cameras.
Mars Climate Orbiter was lost on arrival September 23, 1999. Engineers concluded that the spacecraft entered the planet's atmosphere too low and probably burned up.