Core to Atmosphere Exploration of Ice Giants: A Uranus Mission Concept Study

Ice giants remain largely unexplored, as their large distance from the Sun limits both Earth-based observations and spacecraft visits. The significant occurrence of ice giant-sized planets among detected exoplanets presents an impetus to study Uranus to understand planetary formation, dynamics, and evolution. In addition, Uranus is also uniquely interesting, given the large inclination of its rotation axis and magnetospheric configuration. In this work, we design a mission concept that aims to maximize scientific return by measuring Uranus' chemical composition, internal structure, and magnetosphere, the first two being primary indicators of ice giant formation mechanisms. For this study, we analyze the trade space for a Uranus mission constrained by a cost cap of $1B. We discuss the decision making processes behind our choices of the science priorities, instrument suite and orbital configuration. Trade space decisions include a strong onboard instrument suite in lieu of a descent probe, an orbiter instead of a flyby mission, and design constraints on the power and propulsion systems. The mission, CAELUS (Core and Atmospheric Evolution Laboratory for Uranus Science), is designed for an August 2023 launch. Following a 14-year cruise with multiple planetary gravity assists, the spacecraft would begin its science mission, which consists of a series of ten 30-day near-polar orbits around Uranus. The instrument suite would consist of a microwave radiometer, Doppler seismometer, magnetometer, and UV spectrometer. These four instruments, along with a high-gain antenna capable of gravity science, would provide a comprehensive science return that meets the bulk of the scientific objectives of the 2013 NRC Planetary Science Decadal Survey for ice giants, most notably those regarding the chemical composition, interior structure, and dynamo of Uranus. This mission concept was created as part of an educational exercise for the 2014 Planetary Science Summer School at the Jet Propulsion Laboratory.