Mars Exploration Rover costs per fiscal year. The twin rovers launched in 2003 and began Mars surface operations after their landings in January of 2004. After their prime mission completion 90 days later, both rovers began extended operations. Spirit continued until May of 2011. Opportunity ended in 2018. Source: Planetary Science Budget Dataset, compiled by Casey Dreier for The Planetary Society (accessible on Google Sheets or downloadable as an Excel file).