The continued operation of the Voyager 1 and Voyager 2 spacecraft after their planetary encounters were completed. The power sources on both craft are expected to sustain operation until about 2020. As long as power is available, instruments on board continue to detect particles in the heliosphere, and to measure magnetic field. It is anticipated that they will gather the first scientific data from the region of the heliopause, where the solar wind merges with the interstellar medium.