NASA's Psyche spacecraft will gather science at the asteroid Psyche at four orbit altitudes, as depicted in this graphic. The orbits are named alphabetically from highest (A) to lowest (D), but they don't proceed in alphabetical order. Rather, they proceed based on the changing amount of sunlight illuminating the asteroid's surface during observation and the kind of science that can be done. Because sunlight will illuminate less and less of the asteroid's surface when the first part of Orbit B begins, this orbit is split into two parts, B1 and B2, so that the spacecraft can complete its mapping of the asteroid. The expected order of orbits during Psyche's prime mission is A, B1, D, C, B2.