Comparison of dose and risk estimates between ISS Partner Agencies for a 30-day lunar mission.

The International Partner Agencies of the International Space Station (ISS) present a comparison of the ionizing radiation absorbed dose and risk quantities used to characterize example missions in lunar space. This effort builds on previous collaborative work that characterizes radiation environments in space to support radiation protection for human spaceflight on ISS in low-Earth orbit (LEO) and exploration missions beyond (BLEO). A "shielded" ubiquitous galactic cosmic radiation (GCR) environment combined with--and separate from--the transient challenge of a solar particle event (SPE) was modelled for a simulated 30-day mission period. Simple geometries of relatively thin and uniform shields were chosen to represent the space vehicle and other available shielding, and male or female phantoms were used to represent the body's self-shielding. Absorbed dose in organs and tissues and the effective dose were calculated for males and females. Risk parameters for cancer and other outcomes are presented for selected organs. The results of this intracomparison between ISS Partner Agencies itself provide insights to the level of agreement with which space agencies can perform organ dosimetry and calculate effective dose. This work was performed in collaboration with the advisory and guidance efforts of the International Commission on Radiological Protection (ICRP) Task Group 115 and will be presented in an ICRP Report.

Evolving radiological protection guidelines for exploration-class missions.

International Space Station partner nations have yet to agree on career radiation dose constraints. This is of increasing concern for collaborative mission planning beyond low-Earth orbit, since it is likely that one or two long-duration missions will expose crew to a cumulative dose that approaches or exceeds their current respective limits. As with radiological effects, the cumulative health impact of the numerous other injuries and illnesses documented during spaceflight is inherently heightened with longer and farther missions, say to the Moon and Mars. This paper summarizes the origin of existing radiological constraints employed by the Canadian Space Agency and explores how to build upon these protection practices to address the challenges associated with beyond low-Earth orbit missions. The discussion then leads into a review of conventional risk metrics currently under evaluation by space-faring nations to quantify risk of radiation-induced cancer mortality. This paper concludes with a proposal for the application of an existing burden of disease model termed the Disability Adjusted Life Year, to space exploration. This model can accommodate the many health hazards of spaceflight, including ionizing radiation, on a common scale. It has the potential to serve as an intuitive communication tool for informing on the impact of spaceflight on crew health.

Monte Carlo simulations of the secondary neutron ambient and effective dose equivalent rates from surface to suborbital altitudes and low Earth orbit.

Occupational exposures from ionizing radiation are currently regulated for airline travel (<20 km) and for missions to low-Earth orbit (∼300-400 km). Aircrew typically receive between 1 and 6 mSv of occupational dose annually, while aboard the International Space Station, the area radiation dose equivalent measured over just 168 days was 106 mSv at solar minimum conditions. It is anticipated that space tourism vehicles will reach suborbital altitudes of approximately 100 km and, therefore, the annual occupational dose to flight crew during repeated transits is expected to fall somewhere between those observed for aircrew and astronauts. Unfortunately, measurements of the radiation environment at the high altitudes reached by suborbital vehicles are sparse, and modelling efforts have been similarly limited. In this paper, preliminary MCNPX radiation transport code simulations are developed of the secondary neutron flux profile in air from surface altitudes up to low Earth orbit at solar minimum conditions and excluding the effects of spacecraft shielding. These secondary neutrons are produced by galactic cosmic radiation interacting with Earth's atmosphere and are among the sources of radiation that can pose a health risk. Associated estimates of the operational neutron ambient dose equivalent, used for radiation protection purposes, and the neutron effective dose equivalent that is typically used for estimates of stochastic health risks, are provided in air. Simulations show that the neutron radiation dose rates received at suborbital altitudes are comparable to those experienced by aircrew flying at 7 to 14 km. We also show that the total neutron dose rate tails off beyond the Pfotzer maximum on ascension from surface up to low Earth orbit.