Mars rover to regain contact. Mars 2, Mars 3 were physically tethered probes; "Sojourner" was dependent on the Mars Pathfinder base station for communication with Earth; MER-A & B and "Curiosity" were on their own. Of these "Curiosity" is still active, and "Spirit", "Opportunity" and "Sojourner" completed their missions before losing contact. Seven rovers have been dispatched to Mars: "Examples Landed instrumentation" (Rovers) Mars rovers in development include: One experimental design, not proposed for any actual mission, is: NASA distinguishes between "mission" objectives and "science" objectives. Mission objectives are related to progress in space technology and development processes. Science objectives are met
Mars Surveyor 2001 Lander is identical to that of the Mars Polar Lander, which had been intended to be the first of a series of low-cost "Mars Surveyor" landers sent to Mars. Prior to mission cancellation, cost overruns and technical problems caused the Lander design to be rescoped, and the planned large Athena rover was replaced by a small rover duplicating the "Sojourner" which was a part of the Mars Pathfinder mission. (The Athena did later make it to Mars, however, with two such rovers making up the Mars Exploration Rover Mission of 2004. The second of these, MER-B "Opportunity", landed at Mars Surveyor