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
Opportunity mission timeline Opportunity mission timeline Opportunity, MER-B (Mars Exploration Rover – B), is a robotic rover active on the planet Mars since 2004. Launched on July 7, 2003, "Opportunity" landed on Mars' Meridiani Planum on January 25, 2004 at 05:05 Ground UTC (about 13:15 Mars local time), three weeks after its twin "Spirit" (MER-A), also part of NASA's Mars Exploration Rover Mission, touched down on the other side of the planet. While "Spirit" became immobile in 2009 and ceased communications in 2010, "Opportunity" remains active as of December 11, 2017, having already exceeded its planned 90 sol (Martian days) duration of activity