Test target

A Test Target is a common feature on interplanetary landing craft such as the Viking Lander and Mars Exploration Rovers. The target is usually a visible marker or plate on the exterior of the vehicle, within sight of the lander's imaging system, usually a CCD camera. The target first possesses samples of primary colors and a grey scale. The camera uses this much like a photographer would use a chip chart on Earth; the color samples allow the camera to compensate for white balance and contrast. The target provides a visual reference as well, so that the initial orientation of the camera can be fixed.

On the Mars Exploration Rover, the target was designed with a pillar elevated above the main surface, so that the targe could be used as a sundial.