The Thermal Plasma Sensor (TPS) for the Geospace Dynamics Constellation (GDC) mission

GDC is a six-satellite constellation, designed to investigate the dynamics of the coupling between the ionosphere and thermosphere. The mission will provide multipoint observations of both the energy inputs and the ionosphere-thermosphere system response with sufficient spatial and temporal resolution to finally unravel the physical processes underlying the observed system-level dynamical responses. A critical component of the measurement requirements are the characteristics of the thermal plasma. TPS is a multi-sensor instrument designed to measure the three components of the ion drift, the ion density and temperature, and the mass fractions of the major constituent ions. We present an overview of the instrument, the methods by which the measurements are made, and the science questions to be addressed.