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The 2001 Mars Odyssey spacecraft Martian Radiation Environment Experiment (MARIE) is a solid-state silicon telescope high-energy particle detector designed to measure galactic cosmic radiation (GCR) and solar particle events (SPEs) in the 20 – 500 MeV/nucleon energy range. In this paper we discuss the instrument design and focus on the observations and measurements of SPEs at Mars. These are the first-ever SPE measurements at Mars. The measurements are compared with the geostationary GOES satellite SPE measurements. We also discuss some of the current interplanetary particle propagation and diffusion theories and models. The MARIE SPE measurements are compared with these existing models.

Currently, the exposure limits outlined for crews of the ISS (International Space Station) are based on two principles. The first is that the excess risk to that crewmember be maintained at a level below 3%. The second is that radiation protection personnel must adhere to the ALARA (As Low As Reasonable Achievable) principle. This principle would mandate that for any exposure, the risk incurred as a result be weighed against the social and economic benefits of the activity. An ancillary conclusion of this principle is that if it is possible to lower an exposure through relatively low cost, while not hindering the benefits, then that type of precaution should be pursued. With this in mind, the Space and Life Science Directorate at NASA’s center for manned spaceflight, Johnson Space Center in Houston, has undertaken a project to retrofit radiation shielding into those portions of the ISS where crews are expected to spend larger amounts of time.

Typical calculations of radiation exposures in space approximate the composition of the human body by a single material, typically Aluminum or water. A further approximation is made with regard to body size by using a single anatomical model to represent people of all sizes. A comparison of calculations of organ dose and dose-equivalent is presented. Calculations are first performed approximating body materials by water equivalent thickness', and then using a more accurate representation of materials present in the body. In each case of material representation, a further comparison is presented of calculations performed modeling people of different sizes.

Solar particle events (SPE) are typically dominated by high-energy, low-linear energy transfer (LET) protons. Biological damage to astronauts during an SPE is expected to include a large contribution from high LET target fragments produced in nuclear reactions in tissue. We study the effects of nuclear reactions on integral LET spectra, behind typical levels of spacecraft and body shielding, for the historically largest flares using the high-energy transport code, BRYNTRN in conjunction with several biological damage models. The cellular track model of Katz provides an accurate description of cellular damage from heavy ion exposure. The track model is applied with BRYNTRN to provide an LET decomposition of survival and transformation rates for solar proton events.