Energetic Particle Measurements with Solar Orbiter

Solar Orbiter, a joint ESA/NASA mission, is designed to study the Sun and inner heliosphere in greater detail than ever before. At the closest point on its heliocentric orbit, the Solar Orbiter spacecraft will be just closer than 0.3 AU from the Sun. In addition to providing high-resolution images of the solar surface, perihelion passes at these distances occur in near co-rotation with the Sun, allowing the instruments to track features on the surface for several days. The mission profile also includes a latitude cranking phase that will allow observations above the solar equator. The combination of near-Sun, quasi-heliosynchronous and out-of-ecliptic observations by remote-sensing and in-situ instruments makes Solar Orbiter a unique platform for the study of the links between the Sun and the inner heliosphere. Understanding the physical processes operating in Solar Energetic Particle (SEP) events is a major goal of the Solar Orbiter mission because of the importance of acceleration processes in solar system and astrophysical sites, and because of the potential impact of these events on space hardware. The Energetic Particle Detector (EPD) investigation on Solar Orbiter is a suite of four different sensors plus the instrument control unit to measure the energetic particles from slightly above solar wind energies to hundreds of MeV/nucleon. The EPD addresses one of the key science objectives of ssolar Orbiter, namely "How do solar eruptions produce energetic particle radiation that fills the heliosphere?" In addition, EPD tackles three primary goals of Solar Orbiter: 1) How and where are energetic particles accelerated at the Sun?2) How are energetic particles released from their sources and distributed in space and time?3) What are the seed populations for energetic particles?We describe progress possible with EPD on achieving the science goals of the mission.