Minimum and maximum proton energy spectra of galactic origin observed near Earth (top and bottom continuous lines, respectively). The bottom dot-dashed line represents the minimum proton flux expected during the LISA mission. Dashed lines (December 14, 2006; Adriani et al. (2011)), dotted lines (May 7, 1978; McGuire and von Rosenvinge, 1984) and top dot-dashed lines (February 23, 1956; Vashenyuk et al., 2008) represent solar proton fluxes observed during the evolution of SEP events of different intensities. The vertical black line indicates the maximum energy of the NGRM proton spectrum measurement capability.