The 2001 Surveyor lander spacecraft was built under contract to NASA by the Lockheed Martin corporation. Except for the solar arrays, the basic lander design 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 2001 Lander's target site, Meridiani Planum.)