The drawing outlines essential steps in a Lunar Orbiter mission following launch and transit to the Moon's vicinity. In step 1 the spacecraft fired its velocity control rocket to make a course correction. In step 2 the rocket fired again to deboost the spacecraft into its initial orbit of the Moon. Here its orbit was adjusted, and the first pictures were made (3) before the Orbiter changed orbital parameters (4) to assume an elliptical orbit that brought it closer to the lunar surface for further photographic coverage (5).

Credits - NASA