Chapter 17 - Solar Particle Events and Human Deep Space Exploration: Measurements and Considerations

Abstract

Extreme solar events such as strong flares and coronal mass ejections (CMEs) cause transient sharp increases of the ionizing radiation field in space, enhancing crew exposure in deep space exploration voyages, both during trips and during their stay on a planet's surface. This radiation is made up of electromagnetic waves and also of charged particles (mostly low-energy protons, with spectra mainly below a few hundred MeV), characterized by high fluxes (reaching 106–107 #/(m2ssrMeV)−1), and defined directionality (solar particle events: SPE). In the following we will focus exclusively on the particle component as it is the only one causing safety concerns for the crew. Unprotected crew members would be exposed to high risks, possibly even death. Protection is feasible due to the relatively low energy of the particles; however, it would require an unfeasible amount of mass if the whole spacecraft were to be protected. Different considerations may be used for planetary bases where materials from the planet itself can be used. A generally agreed countermeasure strategy is based on the concept of temporary shelter: a site in the space habitat where the crew can move at a warning signal. The site is small enough that the requested mass becomes feasible. However, this shifts the problem from protection to the ability to issue the warning in due time. As widely discussed in this book, the understanding of solar physics for detailed forecasting of flares and CMEs, and consequently of SPEs, is gaining increasing attention. In this chapter we will show measurements of the radiation environment inside the International Space Station during three intense solar events: December 2006, March 2012, and May 2012. The forecasting requirements needed for human space exploration, the requested high accuracy of which is still far enough from the reliability of the available data, will be addressed, together with possible alternative strategies.