NASA's rovers on Mars are still going after 5 years

Excellent engineering - they were designed to last 90 days and now they both have survived and are still functioning well after 5 years. JPL has some superior engineers, collaboration and processes to have accomplished such a feat. Luck helped a little too - with dust storms cleaning off the solar panels periodically. They also were able to do quite a bit of science and learning how to use the rovers prior to a several month long dust storm shut down operations for a while. Amazingly, both rovers survived that too. JPL does some very good work.

http://edition.cnn.com/2009/TECH/01/03/mars.rovers.five.years/?iref=mpstoryview

Squyres said the journeys had been motivated by science, but had led to something else important.

"This has turned into humanity's first overland expedition on another planet. When people look back on this period of Mars exploration decades from now, Spirit and Opportunity may be considered most significant not for the science they accomplished, but for the first time we truly went exploring across the surface of Mars."