[1] We are preparing to return humans to the Moon and setting the stage for exploration to Mars and beyond. However, it is unclear if long missions outside of low-Earth orbit can be accomplished with acceptable risk. The central objective of a new modeling project, the Earth-Moon-Mars Radiation Exposure Module (EMMREM), is to develop and validate a numerical module for characterizing time-dependent radiation exposure in the Earth-Moon-Mars and interplanetary space environments. EMMREM is being designed for broad use by researchers to predict radiation exposure by integrating over almost any incident particle distribution from interplanetary space. We detail here the overall structure of the EMMREM module and study the dose histories of the 2003 Halloween storm event and a June 2004 event. We show both the event histories measured at 1 AU and the evolution of these events at observer locations beyond 1 AU. The results are compared to observations at Ulysses. The model allows us to predict how the radiation environment evolves with radial distance from the Sun. The model comparison also suggests areas in which our understanding of the physics of particle propagation and energization needs to be improved to better forecast the radiation environment. Thus, we introduce the suite of EMMREM tools, which will be used to improve risk assessment models so that future human exploration missions can be adequately planned for.

1] The Earth-Moon-Mars Radiation Environment Module (EMMREM) is a comprehensive numerical framework for characterizing and predicting the radiation environment of the inner heliosphere. We present a study of the October/November 2003 Halloween solar energetic particle events with an energetic particle acceleration and propagation model that is part of EMMREM, highlighting the current ability of the framework to make predictions at various locations of the inner heliosphere. We compare model predictions with Ulysses observations of protons at energies above 10 MeV in order to obtain realistic proton fluxes and calculate radial gradients for peak fluxes, event fluences, and radiation dosimetric quantities. From our study, we find that a power law with an index of −3.55 at energy of 200 MeV describes the time-integrated energetic proton fluence dependence on radial distances beyond 1 AU for the 2003 Halloween events, and an index of −4.18 is appropriate for peak proton fluxes at that energy. Calculations of radiation doses based on these simulations show average power law indices of −4.32 and −3.64 for peak dose rates and accumulated doses, respectively. In an effort to improve the predictions, we have coupled our kinetic code to results from a 3-D heliospheric magnetohydrodynamic model, WSA/Enlil. While predictions with the coupled model overall show worse agreement than simulations with steady state solar wind conditions for these large events, the capability to couple energetic particle propagation and numerical models of the solar wind is an important step in the future development of space weather modeling.

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1] Solar energetic particles (SEPs) provide a significant radiation hazard for manned and unmanned interplanetary (IP) space missions. In order to estimate these hazards, it is essential to quantify the gradients of SEP intensities in the IP medium. The Earth-Moon-Mars Radiation Exposure Module (EMMREM) is a new project aimed at characterizing the time-dependent radiation exposure in IP space. In this paper, we utilize EMMREM to study the radial dependence of proton peak intensities, event fluences, and radiation dose equivalents of 27-31 May 2003 SEP events at eight different locations between 1 and 4.91 AU at energies between ∼1.5 MeV and ∼130 MeV. We have modeled onset times and intensity profiles of the SEP events at Mars and Ulysses and found very good agreement at different energies. We report observations of energetic particles at locations with magnetic field line footprints that are separated by ∼90°in heliolongitude, possibly indicating very large coronal mass ejection sizes and/or high cross-field diffusion at large radial distances. Our results show that radial dependencies of proton peak intensities exhibit a broken power law between 1 to 2.5 AU and 2.5 to 4.91 AU, ranging between R −2.52 ± 0.42 and R −5.97 ± 0.32 for 25 MeV and between R −2.13 ± 0.36 and R −5.21 ± 0.29 for 52 MeV, where R is the radial distance from the Sun in units of AU. Event fluences exhibit a similar behavior but with a harder spectra. Radiation dose calculations show that these events did not pose a short-term radiation hazard to humans in the IP space. Citation: Dayeh, M. A., M. I. Desai, K. Kozarev, N. A. Schwadron, L. W. Townsend, M. PourArsalan, C. Zeitlin, and R. B. Hatcher (2010), Modeling proton intensity gradients and radiation dose equivalents in the inner heliosphere using EMMREM: May 2003 solar events, Space Weather, 8, S00E07,

For human operations on the surface of Mars, methods of estimating radiation exposures from galactic cosmic rays (GCRs) are needed. To facilitate making estimates of human radiation exposures for crew operations in the Martian atmosphere, lookup tables have been generated that provide doses for critical body organs and effective doses for exposures from galactic cosmic rays anywhere on the surface of Mars. The organ doses and effective doses are tabulated for carbon dioxide atmospheric shielding areal densities ranging from 0 to 300 g cm−2 followed by aluminum spacecraft or habitat shield areal densities ranging from 0 to 100 g cm−2. The Badhwar‐O'Neill GCR model for interplanetary magnetic field potentials, ranging from the most probable solar minimum (currently 417 MV) to solar maximum conditions (1800 MV) in the solar cycle, is used as input into the calculations. This model is the standard one used for space operations at the Space Radiation Analysis Group at NASA Johnson Space Center. Use of the tables is illustrated for an environment consisting of the current galactic cosmic radiation spectrum impinging on an aluminum habitat on the surface of Mars.