The plasmasphere tomography (PlaTo) mission concept

The plasmasphere is the cold, dense torus of plasma extending from the topside ionosphere to approximately two to six Earth radii, containing a significant part of the mass of the magnetosphere. This dense population of plasma influences magnetospheric dynamics and how the solar wind couples to Earth’s ionosphere. It controls key wave–particle interactions that influence the evolution of the radiation belts. The plasmasphere has been studied remotely from the ground using ducted whistler waves, remotely from space using extreme ultraviolet (EUV) imagers and radio sounding, and in situ using plasma waves, spacecraft potential measurements, and retarding potential analyzers (RPAs). The next critical step for understanding plasmasphere dynamics requires following the mesoscale density evolution on temporal cadences of minutes. One way to access these spatial and temporal scales is to leverage space-based radio tomography. This technique is similar to the computed tomography (CT) scan used in medical imaging. Applying this technique to a space plasma environment requires a constellation of spacecraft. A basic mission design that can answer fundamental questions about the physics of the plasmasphere and expand our understanding of how the space environment can impact human activities is explored here. The result is the Plasmasphere Tomography (PlaTo) mission concept, a provisional design that uses a constellation of 14 spacecraft located on two orbits to image the plasmasphere with radio tomography.