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The effects of uncertainties in published proton fluence spectra for large solar particle events (SPE) on organ dose estimates are largely unknown since uncertainties in the measured spectra are unknown. In this work, input spectra for several large SPEs are adjusted by as much as 50% to account for the spectrum uncertainties. The BRYNTRN space radiation transport code and CAM human geometry model are used to perform the calculations. The calculations are made assuming three organ doses and four nominal thicknesses of spacecraft aluminum shielding. Discussions of dose variations for several events based on different spectrum uncertainty values are presented.

Calculations of solar energetic particle event (SPE) doses typically utilize SPE proton spectra parameterized with either an exponential in rigidity (momentum per unit charge) or a Weibull form in energy. In this work we report organ doses calculated using these two different parameterizations of proton spectra of four large solar energetic particle events. They are the SPEs of August 4, 1972, August 12, 1989, September 29, 1989 and October 19, 1989. The variations in predicted doses to critical organs introduced by the use of these two parameterizations for these large events could be a factor in evaluating the effectiveness of spacecraft shielding. Events similar to the largest SPEs observed during the space age could deliver large organ doses and the potential for an acute radiation syndrome response in interplanetary crews.

When planning space missions, radiation effects due to large solar particle events (SPEs) can become a major concern since doses can become mission threatening to both the crew and the spacecraft electronic components. As mission duration increases, the possibility that a significant dose is delivered also increases, especially during the more active parts of the solar cycle. Therefore, a method of predicting when certain limiting doses will be reached following the onset of a large SPE needs to be available. Typical dose versus time profiles of a SPE can be represented by a Weibull functional form, which is comprised of three unknown parameters. Since these dose-time profiles are nonlinear functions, the use of artificial neural networks as the forecasting mechanism is ideal.

The central objective of the Earth-Moon-Mars Radiation Environment Module (EMMREM) project is to develop and validate a numerical module for completely characterizing time-dependent radiation exposure in the Earth-Moon-Mars and Interplanetary space environments. An important step in the process of building this system is the development of the interfaces between EMMREM's internal components, many of which have existed previously as stand-alone simulation codes. This work specifically discusses the development and implementation of the interface, primarily using the Perl scripting language, between two input data set generators, one of which describes the space radiation environment at some desired location, and a space radiation transport and shielding code, BRYNTRN, that provides estimates at fairly short time intervals of dose and dose equivalent behind shielding.

The ultimate limitation to manned exploration of the solar system will likely be cumulative exposure of the crews to penetrating space radiations. The two major sources of these radiations during deep-space missions are solar particle events (flares) and galactic cosmic rays. Methods to estimate crew exposures and to evaluate concomitant shield requirements for these radiation sources are currently under development. Consisting of deterministic space radiation transport computer codes and accurate models of their nuclear interaction inputs, these calculational tools are employed to estimate the composition and thicknesses of candidate shield materials required for spacecraft equipment and crew protection. In this paper, the current status of model and code development is summarized, preliminary estimates of deep-space shield requirements are presented, and an assessment of radiation protection as a potential “showstopper” for manned deep-space missions will be made.

Radiation shielding analyses are performed for a candidate Mars base habitat. The Langley cosmic ray transport code and the Langley nucleon transport code are used to quantify the transport and attenuation of galactic cosmic rays and solar flare protons through both the Martian atmosphere and regolith shielding. Doses at the surface and at various altitudes were calculated in a previous study using both a high-density and a low-density Mars atmosphere model. This study extends the previous low-density results to include the further transport of the ionizing radiation that reaches the surface through additional shielding provided by Martian regolith. A four-compound regolith model, which includes SiO2, Fe2O3, MgO, and CaO, was selected based on the chemistry of the Viking 1 Lander site. The spectral fluxes of heavy charged particles and the corresponding dosimetric quantities are computed for a series of thicknesses in the shield media after traversing the atmosphere.

Radiation shielding analyses are performed for candidate lunar base habitation modules. The study primarily addresses potential hazards due to contributions from the galactic cosmic rays (heavy ions). The NASA Langley Research Center's high energy nucleon and heavy ion transport codes are used to compute propagation of radiation through conventional and regolith shield materials. Computed values of linear energy transfer are converted to biological dose-equivalent using quality factors established by the International Commission on Radiological Protection. Spectral fluxes of heavy charged particles and corresponding dosimetric quantities are computed for a series of thicknesses in various shield media and are used as an input data base for algorithms pertaining to specific shielded geometries. Dosimetric results are presented as isodose contour maps of shielded configuration interiors.

For deep space missions, a major concern is the occurrence of large solar particle events. In this work a dynamic, new type of artificial neural network called a Sliding Time Delay Neural Network that is capable of accurately predicting total dose for an event, from several input doses early in the event, is presented. The network can update its total dose predictions during the event as new input data are received. Results from testing indicate that the network can predict total doses from large events that are outside the training set to within 4% very early in the event.

Judicious shielding strategies incorporated in the initial spacecraft design phase for the purpose of minimizing deleterious effects to onboard systems in intense radiation environments will play a major role in ensuring overall mission success. In this paper, we present parametric shielding analyses for the three Jupiter Icy Moons, Callisto, Ganymede, and Europa, as a function of time in orbit at each moon, orbital inclination, and various thicknesses, for low- and high-Z shielding materials. Trapped electron and proton spectra using the GIRE (Galileo Interim Radiation Electron) environment model were generated and used as source terms to both deterministic and Monte Carlo high energy particle transport codes to compute absorbed dose as a function of thickness for aluminum, polyethylene, and tantalum. Extensive analyses are also presented for graded-Z materials.

The Lunar Orbiter Mission (LRO) is scheduled to launch at the end of 2008. It will carry different instruments to explore a variety of aspects on the Moon's surface. One of the goals of the LRO is to characterize the lunar radiation environment and its biological impacts on humans. For this purpose a collaboration involving research personnel from Boston University, Massachusetts Institute of Technology, The University of Tennessee, The Aerospace Corporation, Air Force Research Laboratory, and the NOAA Space Environment Center successfully proposed to develop a sensor system called the Cosmic Ray Telescope for the Effects of Radiation (CRaTER). CRaTER will be used to examine the Linear Energy Transfer (LET) spectra of solar particle events (SPE) and galactic cosmic radiation (GCR) in Tissue Equivalent Plastic (A-150) material.

Doses to human crews in interplanetary space from energetic Solar Particle Events (SPE) are of a special concern for future lunar missions. The Lunar Reconnaissance Orbiter (LRO) mission, scheduled to launch by the end of 2008 into Lunar orbit, will conduct several exploratory objectives, one of which is characterizing the lunar radiation environment and its biological impacts on humans. Research is currently being conducted for the purpose of developing a sensor system to be flown on the LRO called the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) to measure the Linear Energy Transfer (LET) Spectra of SPE, providing a link between the Moon’s radiation environment and its biological impact on humans.

The highly successful Galileo mission made a number of startling and remarkable discoveries during its eight-year tour in the harsh Jupiter radiation environment. Two of these revelations were: 1) salty oceans lying under an icy crust of the Galilean moons: Europa, Ganymede and Callisto, and 2) the possible existence or remnants of life, especially on Europa, which has a very tenuous atmosphere of oxygen. Galileo radiation measurement data from the Energetic Particle Detector (EPD) have been used (Garrett et al., 2003) to update the trapped electron environment model, GIRE: Galileo Interim Radiation Environment, in the range of L (L: McIlwain parameter – see ref. 6) = 8–16 Rj (Rj: radius of Jupiter ≈ 71,400 km) with plans to extend the model for both electrons and protons as more data are reduced and analyzed.

Ionizing radiation exposures and associated dosimetric quantities are evaluated for the 11-year solar cycle ending in 1986. Solar flare fluences for the 55 largest flares occurring during the cycle are superimposed on the galactic cosmic ray flux. Published summaries of flare data from the Interplanetary Monitoring Platform (IMP)-7 and IMP-8 satellites are used and include flares whose integrated fluences are greater than 107 protons/cm2 for energies in excess of 10 MeV. A standard cosmic ray environment model for ion flux values at solar minimum and maximum is invoked with an assumed sinusoidal variation between the lower and upper limits. The radiation shielding analysis is carried out for equivalent water-shield thicknesses between 2 and 15 g/cm2. Results are expressed in terms of cumulative incurred dose equivalents for deep-space missions lasting between 3 months and 3 years.

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.