You may not know it, but you have a lot in common with the Mars Exploration Rovers.
Stand in the middle of a driveway of gray, crushed stone and your eyes are drawn to the rocks that look different. A few of them are pink or even white. You move toward a white rock, reach out with your arm to pick it up and examine it. Sometimes you get a magnifying glass to look closer. Or you may want to get a hammer to break it open and see what's inside. When you find a rock that looks really cool, you usually want to tell someone about it.
The rovers were built to look for interesting martian rocks. They scan the ground, move toward a selected rock, collect information, and send that information back to scientists here on Earth. Just like you, the rovers have eyes, an arm, mobility, and the ability to communicate.
How does your body compare to the Mars Exploration Rovers?
The "eyes" of the rover belong to Pancam. Pancam is a camera that will give scientists a binocular view of the martian surface. Instead of seeing everything flat, like a photograph, the Pancam can see its surroundings in stereo. This gives the rover depth perception which is very important when you're moving across a surface as rocky as Mars. Depth perception helps the rover judge distances and avoid obstacles. Your eyes do the same for you.
Hold your arm up in the air. Move it around. You can move it from your shoulder, bend it at the elbow and you can twist your wrist. The rover arm was designed to do the same thing. But where you have a joint, the rover has a motor. The rover "shoulder" has two motors. One rotates the arm parallel to the ground. This is a similar motion to you holding your arm straight out from your side and moving it in a circle. The other shoulder motor on the rover lifts the arm up and down. The "elbow" of the rover has a motor that bends the arm. The motor that moves the rover's "wrist" can also move it up and down. The "hand" of the rover is a turret that holds four science instruments. It has a motor that rotates the different instruments into place so they can take turns looking at an interesting target. The turret might rotate the RAT (rock abrasion tool) into position to grind into martian rock and then rotate the microscopic imager into place to get a closer look at the newly exposed surface.
Rover feet and legs
Each rover moves on six wheels - three on one side of its body and three on the other. You don't have six wheels, but you do have two feet and two legs that provide mobility. Your legs also do something very special. Think about what happens when you walk along the narrow curb of a street and then lose your balance. One foot lands on the street and the other stays up on the curb, but you don't fall over. Your body stays level because one leg bends while the other is straight. The rover has a differential that makes one set of wheels go down if the other goes up. This keeps the rover from tipping over because its top stays level to the ground.
Rover mouth and ear
The rover uses its antennas to "listen" for commands from Earth and to "tell" scientists what it has learned. One of its antennas is called the high gain antenna. The HGA provides "direct to Earth" or DTE communication. It sits on top of the rover, sometimes acting like your ear and sometimes like your mouth. In the beginning of a martian day, the rover listens for instructions from scientists. Then it carries out the tasks it is given and uses the HGA to relay the data it has gathered. Transmission of information is at a rapid rate of speed, but this "conversation" can only occur once per day because of the very long distance between Earth and Mars.