Rovers will play a vital role in upcoming Mars missions by enabling science activities at a wide variety of locations even kilometers away from the landing site. On-going technology development efforts at the Jet Propulsion Laboratory include the Long Range Science Rover Task which is prototyping and demonstrating rover technology capable of traversing several kilometers over the Martian surface carrying out a wide variety of science activities. This paper discusses the operational requirements for Mars science rovers and a current prototype Mars rover called Rocky 7.