Recent ice core analyses suggest that the Carrington event of 1859 may have been the largest solar energetic particle event in the past several hundred years. Previous analyses of potential doses to humans and electronics from such an event suggested that a Carrington-like event, with a hard spectrum similar to that of the event of September 1989 could be catastrophic. Subsequent analyses of the 10Be concentration in the ice core data suggest that the spectral hardness of the Carrington event was softer and similar to the August 1972 event. In this work we review the earlier estimates of doses from a Carrington event, and present updated dose estimates for deep space crews and electronics using the Carrington event proton fluence ⩾30 MeV in combination with an event spectrum similar to that of the August 1972 event. Potential ramifications of these doses for humans and electronics on deep space missions are discussed.

Earlier particle experiments in the 1970s on Pioneer-10 and -11 and Voyager-1 and -2 provided Jupiter flyby particle data, which were used by Divine and Garrett to develop the first Jupiter trapped radiation environment model. This model was used to establish a baseline radiation effects design limit for the Galileo onboard electronics. Recently, Garrett et al. have developed an updated Galileo Interim Radiation Environment (GIRE) model based on Galileo electron data. In this paper, we have used the GIRE model to reassess the computed radiation exposures and dose effects for Galileo. The 34-orbit 'as flown' Galileo trajectory data and the updated GIRE model were used to compute the electron and proton spectra for each of the 34 orbits. The total ionisation doses of electrons and protons have been computed based on a parametric shielding configuration, and these results are compared with previously published results.

Doses in critical body organs of human crews in interplanetary space from energetic solar particle events (SPE) vary widely with the size and spectral hardness of the event. In this work, we present a study of the sensitivities of calculated doses to the skin, ocular lens of the eye, and bone marrow, for crewmembers in deep space, to variations in solar energetic particle event fluence levels and spectral hardness. The calculations are performed by incrementally varying the fluence levels and spectral hardness and tracking changes in organ doses as a function of these variations. For simplicity in interpreting the results, we use the rigidity parameterization form for the SPE integral fluences. It was found that for harder spectra the doses are much larger and decrease less rapidly with increased shielding.

One of the hazards faced by crews of spacecraft in space is exposure to ionizing radiation in the space environment. The main sources of these radiations are the trapped radiation in the Van Allen belts, consisting mainly of protons in the inner belt and electrons in the outer belt, the galactic cosmic ray (GCR) background, composed of all naturallyoccurring elements, and solar energetic particles, produced by events, such as coronal mass ejections and associated phenomena on the Sun. As these radiations pass through spacecraft shielding, their energies and composition are altered by atomic and nuclear interactions with the shielding. Transport of the space radiation fields, as they pass through shielding and body materials, can be mathematically simulated by transport codes utilizing either solutions of the Boltzmann equation or Monte Carlo techniques, obtained by balancing changes in particle fluxes as they traverse a small volume of material with the gains and losses caused by atomic and nuclear collisions. Recently, the Monte Carlo radiation transport code HETC, originally developed at Oak Ridge National Laboratory, has been extended to include heavy ion nuclear interaction models and the associated software modifications needed for heavy ion tracking [1]. The resulting code, called HETC-HEDS (High Energy Transport Code Human Exploration and Development of Space), is capable of carrying out three-dimensional transport of all components, including heavy ions, of the space radiation environment. In this work we present an overview of the current status of code development and present comparisons of predictions from this newly-developed tool with recent laboratory beam measurements of the fluences of secondary particle species produced by the interactions of cosmic ray heavy ion species with thick targets. We also present comparisons of the code predictions with predictions from the PHITS code, recently developed by researchers in Japan.

Solar particle events (SPEs) represent serious concerns to humans and onboard systems in space. Historically, passive bulk shielding, usually aluminum, has been used to minimize space radiation exposures and subsequent physical and biological effects. In this paper, a review of the major SPEs that have occurred in the last 50 years is presented. Prior to 1976, historical SPE particle spectra were obtained from pre-GOES (geostationary orbiting environmental satellite) spacecraft such as the IMP (interplanetary monitoring platform) -34 and -41 spacecraft. For the time period 1976 to current, the GOES SEM (space environment monitor) SPE particle data were used for several of the larger SPEs in this parametric shielding study. SPE particle spectra were calculated for LEO (low Earth orbit) and for the lunar and Mars environments. Using these particle spectra as input source terms and selected high-energy particle transport codes, both deterministic and Monte Carlo, the results of a parametric shielding study using both low-Z and high-Z materials are discussed. Multiple radiation transport codes were used to inter-compare the results for validation and to present benchmark results for the space community.

This paper presents a study of the sensitivities of calculated doses to the skin, ocular lens of the eye and bone marrow, for crewmembers in low Earth orbit, to variations in solar energetic particle event fluence levels and spectral hardness, spacecraft orbital inclination, geomagnetic field storm levels (Kp index), and spacecraft shielding thickness. In general, doses increase for higher inclination orbits, for higher Kp indices, and for harder SPE spectra. The predicted doses sometimes change dramatically for even small variations in the assumed conditions. For large events in high inclination orbits, with a highly disturbed geomagnetic field, doses can be very hazardous to crews.