Implications of the space radiation environment for human exploration in deep space

Abstract

Human exploration of the solar system beyond Earth's orbit will entail many risks for the crew on these deep space missions. One of the most significant health risks is exposure to the harsh space radiation environment beyond the protection provided by the Earth's intrinsic magnetic field. Crew on exploration missions will be exposed to a complex mixture of very energetic particles. Chronic exposures to the ever-present background galactic cosmic ray (GCR) spectrum consisting of all naturally occurring chemical elements are combined with sporadic, possibly acute exposures to large fluxes of solar energetic particles, mainly protons and alpha particles. The background GCR environment is mainly a matter of concern for stochastic effects, such as the induction of cancer with subsequent mortality in many cases, and late deterministic effects, such as cataracts and possible damage to the central nervous system. Unfortunately, the actual risks of cancer induction and mortality owing to the very important high-energy heavy ion component of the GCR spectrum are essentially unknown. The sporadic occurrence of extremely large solar energetic particle events (SPE), usually associated with intense solar activity, is also a major concern for the possible manifestation of acute effects from the accompanying high doses of such radiations, especially acute radiation syndrome effects such as nausea, emesis, haemorrhaging or, possibly, even death. In this presentation, an overview of the space radiation environment, estimates of the associated body organ doses and equivalent doses and the potential biological effects on crew in deep space are presented. Possible methods of mitigating these radiations, thereby reducing the associated risks to crew are also described.

Shielding evaluation for solar particle events using MCNPX, PHITS and OLTARIS codes

“…Most SPE events originating from an eruption of solar flares during an 11-year solar cycle are of low intensity and energy that present less damage to living organisms and electronic components. Typical shield materials and design provide adequate protection from such events (Wilson, 2004;Townsend, 2005). On rare occasions, the mass ejection of solar particles near the Sun's corona occurs, resulting in some large SPE events during the solar cycle.…”

“…These factors affect the integral quantities significantly. Table 2 provides a summary of efforts that report dose and dose equivalent results for SPE spectra transported through aluminum slab thickness of 10 to 20 g/cm 2 (Hoff et al, 2004;Townsend, 2005;Wilson et al, 2006;Heinbockel et al, 2011;and Lin et al, 2012). Although the results summarized in the table are from the last 10 years, the differences in codes, code versions and the methods used for dose and dose equivalent calculations must be noted.…”

“…For example, the difference in codes and code version is evident when the reported codes in these papers are compared. The results reported in Hoff et al (2004), and Townsend (2005) studies use the BRYNTRN code. This is the light ion transport subset of the HZETRN code (Wilson et al, 1989;Shinn et al, 1994).…”

Space: The Final Frontier for IR

“…Radiation exposure is expected to pose a major challenge for interplanetary travel (2,(25)(26)(27). Whereas a trip to the moon involves a dose of approximately 5 mSv, a trip to Mars may involve doses exceeding 2,000 mSv and greater exposure to high-dose stochastic events such as solar flares, coronal mass ejections, or gamma-ray bursts (2,(25)(26)(27)(28).…”

“…Whereas a trip to the moon involves a dose of approximately 5 mSv, a trip to Mars may involve doses exceeding 2,000 mSv and greater exposure to high-dose stochastic events such as solar flares, coronal mass ejections, or gamma-ray bursts (2,(25)(26)(27)(28). In such conditions, familiarity with occupational monitoring, activity modification for dose minimization, and treatment of acute radiation sickness will be important.…”