The Solar Monitoring with Ions and Langmuir Instrument for the Next Generation (SMILING) mission is currently being developed in collaboration between researchers at Mahidol University and engineers at the National Astronomical Research Institute of Thailand (NARIT). The mission goals address space situational awareness, including space weather monitoring and observing the temporal variations of solar energetic particle and Galactic cosmic ray fluxes and their correlations between two identical 3U CubeSats, which will have sun-synchronous low Earth orbits with different orbital periods at altitudes of 500 - 600 km. The Solar Monitoring by Ions of Light Elements (SMILE) payload will detect incoming ions using 2 layers of position-sensitive detectors made from plastic scintillator fibers. The particle's deposited energy is measured by a semiconductor detector based on a P-I-N junction and BGO scintillators for ion identification using the $\Delta$E–E technique. The expected geometrical acceptance and cosmic-ray count rates calculated from Geant4 simulation will be indicated. Local plasma parameters such as electron density and temperature will be measured at each satellite by a Langmuir probe, the Langmuir Instrument for the Next Generation (LING).