The Integrated Science Investigation of the Sun (ISʘIS) is a complete science investigation on the Parker Solar Probe (PSP) mission, which flies to within nine solar radii of the Sun’s surface. ISʘIS comprises a two-instrument suite to measure energetic particles over a very broad energy range, as well as coordinated management, science operations, data processing, and scientific analysis. Together, ISʘIS observations allow us to explore the mechanisms of energetic particles dynamics, including their: (1) Origins — defining the seed populations and physical conditions necessary for energetic particle acceleration; (2) Acceleration — determining the roles of shocks, reconnection, waves, and turbulence in accelerating energetic particles; and (3) Transport — revealing how energetic particles propagate from the corona out into the heliosphere.
The two ISʘIS Energetic Particle Instruments measure lower (EPI-Lo) and higher (EPI-Hi) energy particles. EPI-Lo measures ions and ion composition from ~20 keV/nucleon–15 MeV total energy and electrons from ∼25–1000 keV. EPI-Hi measures ions from ~1–200 MeV/nucleon and electrons from ~0.5–6 MeV. EPI-Lo comprises 80 tiny apertures with fields-of-view (FOVs) that sample over nearly a complete hemisphere, while EPI-Hi combines three telescopes that together provide five large-FOV apertures. ISʘIS observes continuously inside of 0.25 AU with a high data collection rate and burst data (EPI-Lo) coordinated with the rest of the PSP payload; outside of 0.25 AU, ISʘIS runs in low-rate science mode whenever feasible to capture as complete a record as possible of the solar energetic particle environment and provide calibration and continuity for measurements closer in to the Sun. The ISʘIS Science Operations Center plans and executes commanding, receives and analyzes all ISʘIS data, and coordinates science observations and analyses with the rest of the PSP science investigations. Together, ISʘIS’ unique observations on PSP will enable the discovery, untangling, and understanding of the important physical processes that govern energetic particles in the innermost regions of our heliosphere, for the first time.