NASA's robots have gotten bigger, better, more productive, and more powerful.
Ken Kremer of Universe Today highlighted a wonderful image that shows you the evolution of NASA's Mars rovers in a single photograph. The rovers you see were obviously not flown to Mars, but represent very similar test units. The photograph was taken at the Jet Propulsion Laboratory's "Mars Yard," which provides simulated Martian terrain for testing. (You can see a panorama of the yard here.)
Sojourner, which launched in 1996 and landed in 1997, was part of the Mars Pathfinder Mission. The itty-bitty rover weighed in at 23 pounds. It was 26 inches long, 19 inches wide, and 12 inches tall. In 83 Martian days of operation, Sojourner never ventured more than 40 feet away from its lander, and its odometer for the whole trip read only about 330 feet. The rover snapped 550 photographs and did a tiny amount of spectroscopy on a rock named Yogi.
The Spirit and Opportunity rovers took our Martian meanderings to the next level when they landed three weeks apart in 2004. They were bigger than Sojourner -- 7.5 feet long, 5 feet wide, 5 feet tall, 400 pounds -- and built to last on the surface of Mars for longer than Sojourner. As it turned out, they far exceeded their initial mission duration. Spirit was scooting around the surface of Mars until 2009, when the rover got stuck and eventually lost communication with NASA. Opportunity is still going strong, having logged 3,116 days and over 21 miles of travel on the planet.
Which brings us to the star of last night's show, Curiosity, previously known as the Mars Science Laboratory. It weighs 2000 pounds and has a planned mission duration of 23 Earth months, which it could exceed by quite some time, based on NASA's experience with the Spirit and Opportunity rovers. It is, as @SarcasticRover put it, essentially a nuclear-powered SUV in that it is powered by 11 pounds of plutonium's decay. The heat generated in that process is directly converted into electricity by a small generator like the ones that powered the Viking and Voyager missions to Mars and the outer solar system, respectively. It has a minimum lifespan of 14 years and a higher power output (2.5 kilowatt hours vs 0.6 kilowatt hours per day) than the last generation of rovers. True to its old name ('Mars Science Laboratory'), Curiosity is packed with instruments as we detailed earlier this year.