Whitepaper #169 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: outer heliosphere; space-based missions/projects; emerging opportunities.
Flying a capable galactic cosmic ray (GCR) experiment on an Interstellar Probe (ISP) mission that launches around 2036 will provide the measurements needed to resolve the GCR puzzles by the end of the current century, cap-stoning ~200 years of cosmic ray science. The GCR experiment needs to be in the local interstellar medium, the one place where the uniquely revealing low-energy GCRs are found.