The thermal environment for Mars surface exploration provides unique challenges for materials for use in structure and thermal control. The Sojourner Mars Rover has a lightweight integrated structure/insulation that has been environmentally tested and qualified for the Pathfinder mission to Mars. The basic structure with insulation, called the Warm Electronics Box (WEB), accounts for only 10% of the total Rover mass. The WEB is a thermal isolating composite structure with co-cured thermal control surfaces and an ultra-lightweight hydrophobic solid silica aerogel which minimizes conduction and radiation. This design provides excellent thermal insulation at low gas pressures and meets the structural requirements for spacecraft launch loads and for a 60 g impact landing at Mars without damage to the insulation or structure. Since the Pathfinder mission, this basic design concept has been developed and improved for future Mars surface robotic missions.