This grouping of two test rovers and a flight spare provides a graphic comparison of three generations of Mars rovers developed at NASA Jet Propulsion Laboratory, Pasadena, Calif. The setting is JPL Mars Yard testing area.

Two spacecraft engineers stand with three generations of Mars rovers developed at NASA JPL, Pasadena, Ca. Front and center is a flight spare of Sojourner, left is a working sibling to Spirit and Opportunity, right is test rover Curiosity.

Two spacecraft engineers stand with three generations of Mars rovers developed at NASA JPL, Pasadena, Ca. Front and center is a flight spare of Sojourner, left is a working sibling to Spirit and Opportunity, right is test rover Curiosity.

This grouping of two test rovers and a flight spare provides a graphic comparison of three generations of Mars rovers developed at NASA Jet Propulsion Laboratory, Pasadena, Calif. The setting is JPL Mars Yard testing area.