The radiation environment in space is a complex mixture of particles of solar and galactic origin with a broad range of energies. In astronaut dose estimation, three sources must be considered: galactic cosmic radiation, trapped particles, and solar energetic particles (SEPs). The astronaut dose due to SEP exposure during a space mission is more difficult to estimate than the other components because the occurrence of a large solar particle event cannot be predicted by the current space weather research. Thus, several models have been proposed to estimate the worst-case scenario and/or the probability of the integral SEP fluence during a particular space mission, considering the confidence level, solar activity, and duration of the mission. In addition, recent investigations of the cosmogenic nuclide concentrations in tree rings and ice cores have revealed that the sun can cause solar particle events much larger than the largest event recorded in the modern solar observations. If such an extreme event occurs during a mission to deep space, astronauts may suffer from radiation doses in excess of the threshold value for some tissue reactions (0.5 Gy) and their career limit (0.6–1.2 Sv). This article reviews the recent progress made in space weather research that is useful for cosmic radiation dosimetry.