The Neptune Odyssey mission concept is a Flagship-class orbiter and atmospheric probe to the Neptune-Triton system. This bold mission of exploration would be the first to orbit an ice giant planet to study the planet, its rings, small satellites, space environment, and the planet-sized moon, Triton, itself a captured dwarf planet from the Kuiper Belt and a geophysically reactivated twin of Pluto. Odyssey addresses Neptune system-level science, with equal priorities placed on Neptune, its rings, moons, space environment, and Triton. Broadly, the mission addresses the following questions: (1) How do the interiors and atmospheres of ice giant (exo)planets form and evolve? (2) What causes Neptune’s strange magnetic field, and how do its magnetosphere and aurora work? (3) Is Triton an ocean world? What causes its plumes? What is the nature of its atmosphere? (4) How can Triton’s geophysics and composition expand our knowledge of dwarf planets like Pluto? (5) What are the connections between Neptune’s rings, arcs, surface weathering, and small moons. To address these questions, a family of high-heritage instruments was chosen for both the orbiter and probe. Cruise observations (e.g., stereo observations of the edges of our heliosphere, asteroid and Centaur flybys, and using Odyssey’s cameras for a rear-view look back at our solar system) would sustain interest and provide unprecedented opportunities for discovery. Finally, equipping both the orbiter and probe with cameras specially purposed for public engagement will help to share the joy of exploration and discovery with those who help make space exploration possible—the general public.
The spacecraft would launch in 2033 on a SLS (or equivalent launch vehicle) on a 16-year cruise to Neptune for a 4-year prime orbital mission. Odyssey would orbit Neptune retrograde (prograde with respect to Triton), providing New Horizons-quality science from Triton every month, using the moon’s gravity to shape the orbital tour and allow coverage of a range of latitudes and longitudes on Triton, on Neptune, and in the space environment. Our example spacecraft will launch with 3520 kg to Neptune orbit and utilize 3 RTGs (radioisotope thermoelectric generators). The atmospheric entry probe would descend in ~37 minutes to the 10-bar pressure level in Neptune’s atmosphere just before Odyssey’s orbit-insertion engine burn. The mission concept is presented at a maturity level of 4 and a total modeled cost (incl. 50% margin) of less than $3.4B; this is a mission NASA could choose to stand up now without waiting for significant advances in technology.