A comprehensive knowledge of the Martian climate requires a better understanding of the formation and evolution of the polar caps. Accurate measurements of mass, volume, and composition of the seasonal polar deposits would enable a precise characterization of the surface-atmosphere interactions relevant to the CO₂ cycle. The acquisition of these science data is only possible through a dedicated orbital mission at Mars. ORACLE (Orbital Radio science and Altimetry for CLimate Experiment) is a mission concept that enables the monitoring of the CO₂ mass exchange between the polar caps and the atmosphere with a pair of spacecraft in a 250×320 km orbit about Mars. A preliminary design of the mission configuration is presented in this study including the scientific payload that consists of a radio science system for inter-satellite tracking, a laser altimeter, and an infra-red camera. These instruments also provide data that are fundamental to investigate Mars’ internal structure and atmosphere. ORACLE is, therefore, a multi-disciplinary mission that is conceived to fulfill the constraints of a medium-class mission.