Three Generations of Mars Rovers with Standing Mars Engineers The rovers are pictured here with real Mars Engineers to get a sense of size and perspective. Front rover is the flight spare for the first Mars rover, Sojourner. At left is a Mars Exploration Rover Project test rover, working sibling to Spirit and Opportunity. At right is a Mars Science Laboratory test rover the size of Curiosity which is targeting a August 2012 Mars landing. The Mars engineers are JPL's Matt Robinson, left, and Wesley Kuykendall. Credit: NASA/JPL-Caltech