Optical navigation involves using a camera or cameras on a spacecraft to take pictures of a target body or bodies during a mission. Those pictures are then used to determine the position of the spacecraft with respect to the target.
"It's really watching where you're going by opening the spacecraft's 'eyes,' or cameras, and looking at the position of the target body in the field of view of the camera," said Dr. Steve Synnott, the principal investigator for this experiment.
The camera on the orbiter will be used to take pictures of the small Martian moons Deimos and Phobos against the background of stars. From the locations of these moons against the star background, engineers can determine the position of the spacecraft with respect to Mars.
If the body - a planet, a moon, a comet or asteroid - does not appear in the expected position in the image, then a trajectory correction maneuver (the firing of a spacecraft's propulsive rockets, used by navigators to change a spacecraft's course) may have to be done. Or, later, engineers would have to fine-tune where to point the cameras so that higher-resolution pictures can be taken of the surface of Mars for science purposes.
The camera on the Mars Reconnaissance Orbiter is not much larger than a manual 35-millimeter camera with a long zoom lens attached. It weighs only 2.8 kilograms (6 pounds) and is about 30 centimeters (12 inches) long and has an aperture (opening) of 60 millimeters (2.4 inches) in diameter.
Approximately 500 pictures will be taken, starting at about 30 days before Mars orbit insertion (March 10, 2006). Most will be taken within the last eight days for maximum accuracy for the orbiter's insertion into Mars' orbit. The accuracy may be about 1 kilometer (a little more than half a mile). These images won't be close-ups, as "pretty portraits" of the moons aren't what navigators are looking for. It is most important for them to see the moons in comparison to stars in the sky to determine the spacecraft's position with accuracy.
This small camera is also being proposed to fly on other NASA missions, possibly to Mars, but also to comets, asteroids and other planets. The increased precision that the camera will provide may prove vital to landed Mars missions that will involve avoiding large obstacles (such as rocks and craters) on the surface.
Moving at approximately 8,250 miles per hour (13,277 kilometers per hour), Mars Reconnaissance Orbiter is currently about 12,897,847 miles (20,757,073 kilometers) from Mars.