The Neptune Atmospheric Retrograde Orbiter (NEPARO) mission concept foresees a large-scale interplanetary science mission to the outer solar system, namely Neptune with its system of rings and moons. A particular focus is set on Neptune’s largest moon, Triton. This mission concept aims to study the feasibility of such a large-scale, multi-decade mission and perform some technical design trade-offs. As an overarching concept, the spacecraft will benefit from spaceflight-proven hardware and novel technological concepts, such as an aeroshell for aerocapture into orbit, optical telecommunications from the outer solar system, next-generation radioisotope thermoelectric generators, and a deployable high-gain antenna.