The Interstellar Probe StudyChallenges of Long Duration Missions

The goal of an interstellar probe is to sample the environment of the local interstellar medium. Only the Voyager spacecraft have approached this region at distances greater than 125 Astronomical Units (AU) for Voyager 1 and 102 AU for Voyager 2, and after some 43 years of flight. To really sample this region distances of over 250 AU will be required. And, mission durations of 50+ years will be required! The Interstellar Probe Study is analyzing the requirements for such a mission and developing concepts for a "pragmatic" implementation of it. By "pragmatic" it is meant that only technologies that can reasonably be expected to be mature in time for a possible launch in 2020 are assumed. In concert with the development of the mission concept, the challenges associated with such a long duration must be assessed, with risks and their mitigation identified. As part of the Interstellar Probe Study, a supporting Lifetime Study has been undertaken. Its focus is on the reliability of the spacecraft, the stability of the ground system and the supporting organizations, and the "human element" - how to maintain the continuity of the team when more than one generation of scientists and engineers will be required to successfully carry out the mission. This paper will provide insight into the challenges identified; the processes used to assess risks and their mitigations; and, some preliminary results of this ongoing task.