The idea behind a rover is very simple: It's a box with a computer in it, six wheels, and a bunch of cameras attached.

But a rover itself is not so simple. Hundreds of people worked in teams to design the rovers, build rockets to propel them into space, make airbags to protect them from a bumpy landing, write programs to control their wheels and cameras, and find an interesting spot to land.

Every day, I go to the NASA Ames Research Center in Mountain View, California, to work on a rover named K-9. You've probably never heard of K-9, since it will never go to Mars. In fact, it rarely leaves my building.

K-9 is kind of a test robot. It's similar to the rovers that will be sent to Mars, and we use them to develop programs and try out scientific instruments before they are put on the actual rover.

We have spent the last five years working on software to control the robot during the long parts of the day when it can't hear from Earth. These programs allow the scientists to give the robot a goal like "go to that rock over there and put your microscope on it." The next time the robot talks to Earth, it will have carried out those tasks and automatically sent back pictures of what it found.

Spirit and Opportunity

In the last few months before the robot is launched, it is sent to NASA's Kennedy Space Center in Florida. The engineers there put on the finishing touches and load it into the rocket for launch. On June 10, 2003, Spirit was launched, and on July 7, 2003, Opportunity was launched on its trip to Mars. The trip takes six months. Scientists don't want to waste those six months, so the robots are launched before the programs are all done.

Last January, six years after we started, the rovers landed on Mars. We sent them their control programs, and they rolled off the landers and into the Martian distance. To many people, that's when the adventure began. But for those of us here at NASA who have been working on the rovers for years, that was one big step in a long journey.

Salvatore Domenick Desiano is a research scientist working at the NASA Ames Research Center.