Voyager 1's original attitude-control system showed slowly increasing signs of trouble in the past two years, said Tim Hogle, a flight-team engineer. Diagnostics pointed to an electronic component that takes analog signals from position-sensing devices and converts them into digital values for an onboard computer. Because of the system's design, switching to that component's backup also meant activating the backup Sun sensor and star tracker, which provide the reference points for the spacecraft's orientation in space.