How does a Mars rover fix itself with no mechanic?

Have you ever pushed a toy car that suddenly would not roll, and a grown-up helped you fix it? Far away on Mars, a robot car called a rover rolls over red dust and crunchy rocks. No mechanic lives there, and nobody can drive over with a toolbox.

So what happens when something on the rover goes wrong? Who helps it, so far from home? How does a Mars rover fix itself with no mechanic?

Inside the rover, a computer checks the rover's own parts all day long. It watches how warm they are, how much power they have, and whether the wheels and arm move the right way. That is how the rover notices when something is wrong.

When the computer finds a problem, the rover stops its work and goes into safe mode, which means resting quietly and waiting for help. In safe mode, the rover keeps itself warm and keeps listening for messages. Stopping keeps a small problem from growing into a big one.

Next, the rover sends a radio message all the way to Earth. The message tells the team back home which part is having trouble. It travels across dark space for many minutes before it arrives.

On Earth, the rover's engineers read the message. Engineers are the people who build machines and look after them. They are the rover's mechanics, but they work from very far away, studying the clues to figure out what went wrong.

The engineers think up a fix, but they cannot try it out on Mars first. A wrong fix could hurt the rover, and nobody could fly there to help. What do you think they do to make sure their fix is safe?

They test it on a twin rover here on Earth! The engineers keep a copy of the rover in a big yard full of sand and rocks. When the fix works on the twin, they know it is safe to send.

Then the engineers send the fix to Mars as new instructions by radio. The instructions show the rover a new way to do its job. With a new way around the trouble, the rover can keep working, even when a broken part cannot be mended.

The rover reads the new instructions and follows them, step by step. It never picks up a tool, because the whole fix arrives by radio. Then the rover comes out of safe mode and rolls on to explore again.

Let's remember two words: safe mode, engineers. A rover's computer spots a problem and rests in safe mode, then engineers on Earth test a fix and send it by radio, and the rover follows the new instructions.

Goodnight, little explorer, and may your dreams roll gently over the red hills of Mars.