Design of a low cost mission to the Neptunian system

Visited only by Voyager 2 in 1989, Neptune and its moon Triton hold important clues to the formation and evolution of the solar system and exoplanetary systems. Neptune-sized planets are the most commonly discovered exoplanets to date. Neptune, an ice giant, is theorized to have migrated from its formation location in the early solar system. This migration affects the expected interior structure, composition, and dynamical evolution of the planet. Triton is conjectured to be a heavily-processed, captured Kuiper Belt Object (KBO), a remnant from the early solar nebula and unique in our solar system. Triton may possess a subsurface aqueous ocean, making it an important astrobiological target. The 2013-2022 Planetary Science Decadal Survey [1] identified a number of high priority science goals for the Neptunian system, including understanding the structure, composition, and dynamics of Neptune´s atmosphere and magnetosphere, as well as surveying the surface of Triton. Following these guidelines, we present a low cost flyby mission concept to Neptune and Triton: TRIDENT (Taking Remote and In-situ Data to Explore Neptune and Triton). TRIDENT would carry six instruments and a government furnished atmospheric probe and would provide significant improvements over the scientific measurements undertaken by Voyager 2. In this paper, we first provide a detailed overview of the science questions pertaining to Neptune and Triton and of the science investigations necessary to elucidate them. We then present the design of TRIDENT´s instrument suite, the trajectory and the spacecraft, as well as the motivation behind each of our choices. In particular, we demonstrate that, for a mission launched on an Atlas V 551, a Neptune orbiter mission would be infeasible with current technology levels without the use of aerocapture. We therefore present a flyby mission concept with a cost lower than FY2015 $1.5B. We also show that the proposed mission has low risk and significant margin and - hat several de-scope options are available in the event of cost overruns. This study was prepared in conjunction with the NASA 2013 Planetary Science Summer School. The work presented is a hypothetical mission proposal, for planning and discussion purposes only. It does not represent NASA´s interests in any way.