Word on the USGS's street is that Landsat 5, the earth observation satellite responsible for continuously taking photos of the earth's surface, is nearing the end of its lifespan. Landsat imagery has been recorded since 1972, meaning that I could very easily click on http://landsat.usgs.gov/ and go back and watch the world change every year since my old man was a sophomore in high school. While being able to retroactively watch my native Northeast Ohio be deforested and suburbanized and dead zones grow in Lake Erie and the Gulf of Mexico is impressive, what's more impressive is that Landsat imagery has remained a FREE program. As Adam Ferrand of the UN Food and Agriculture Organization said:
"The opening of the Landsat archive to free, web-based access is like giving a library card for the world's best library of Earth conditions to everyone in the world."
Big ups to Landsat 5 for going longer than I've been alive and to the Landsat program for going longer than the Star Wars franchise has persisted (For the record, more people will remember Landsat's imagery than the four most recent Star Wars movies - you heard it here). Even bigger ups to the scientists and engineers who have made the Landsat mission such a massive success over the years.
If you want updates on the history of Landsat as a USGS program, including the timeframe of the Landsat 5 mission, I encourage you to check out http://landsat.usgs.gov/ and read up, download some data and check out the different projects Landsat has enabled over the years.