To help future missions in the Mars Exploration Program, Mars Reconnaissance Orbiter carried an optical navigation camera. From 30 days to 2 days prior to Mars Orbit Insertion, the spacecraft collected a series of images of Mars' moons Phobos and Deimos. By comparing the observed position of the moons to their predicted positions relative to the background stars, the mission team accurately determined the position of the orbiter in relation to Mars.
While not needed by Mars Reconnaissance Orbiter to navigate to Mars, the data from this experiment demonstrated that this technique could be used by future spacecraft to ensure their accurate arrival. Accuracy is important to future landers and rovers that need extremely precise navigation to get to their landing sites safely.
