long-scale variations of solar activity, including 14C records in tree rings, nitrate and 10Be deposits in polar ice, and even studies of radioisotopes in lunar rocks. Further analysis of these resources could lead to a better understanding of how intense GCR flux could be for future missions.
The studies used to determine long-scale variability in the GCR can also be used to address a related question of high significance to astronauts, which is, How bad can an SEP event be? Knowing how intense an SEP event could be is important to mission design and also to the development of surface operations concepts. There exist only a few decades of direct observation of SEP events, and so only a few major storms such as the August 1972 event have been measured. In order to provide mission planners with guidelines for “worst case” events, the community frequently chooses multiples of a well-known large event (say, two