NASA's workhorse satellite Landsat 5 recently passed the 20 year mark of operations, beating original estimates that it would only last 2-3 years. Over the course of 100,000 orbits, the satellite has taken over 29 million images of the Earth, tracking human activity and changes in the planet's environment; and it's still working fine. Nothing lasts forever, though; the satellite is expected to run out of fuel by 2009 - a replacement should be launched before then.