The computer, heaters, motors to rotate the solar arrays, and some other devices are essential to getting into safe mode. One of them is to turn to point at the Sun, ensuring that the large solar arrays are fully illuminated. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDASome of the time, the solar arrays will face away from the Sun and the battery will drain. Some of the time the solar arrays will point at (or near) the Sun just by luck. At Dawn's distance from the Sun, a little bit of that faint light on the solar arrays is not sufficient.