Solar wind is ~95% protons, ~4% helium ions, and ~1% heavy ions with light ion energies from ~1 keV to ~10 keV. Light ion energies are modest, but they may represent a radiation damage concern for space exposed materials on the exterior of spacecraft for long duration missions. Examples where light ion radiation damage may be important are thin materials and material applications where surface properties are mission critical including thermal control coatings, solar sail propulsion systems, sunshades, multilayer insulation, and optical thin film coatings.

 A plasma moment approach is used by the space science community which yields proton flux and annual fluences of ~10^8 protons/cm^2-sec and ~10^16 protons/cm^2, respectively, at distances of 1 AU from the Sun. A new “cumulative proton flux” concept suggests solar wind proton flux and annual fluences are really on the order of 10^12 protons/cm^2-sec and 10^19 protons/cm^2, respectively (c.f., Sznajder et al., 2014, 2018, 2021). Laboratory tests of soft metals exposed to protons at the higher flux and fluence levels demonstrate blister formation within a period of a few days at 1 AU with an accompanying change in thermo-optical parameters. 

This new work has serious implications for space exploration because it may restrict material selection for exterior surfaces of spacecraft where thermo-optical properties are important. It is therefore important to determine the best approach for computing proton flux and fluence to guide laboratory tests for qualifying materials and applying test results to selection of materials for use in solar wind environments at the Sun-Earth Lagrange points, exploration of the Moon, and transit between the Earth and Mars. This paper investigates measurement and analysis techniques used to compute solar wind ion flux with a goal of resolving the discrepancy between the traditional and “cumulative proton flux” approaches.