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The development of “next generation” human-rated space vehicles, surface habitats and rovers, and spacesuits will require the integration of low-cost, lightweight materials that also include excellent mechanical, structural, and thermal properties. In addition, it is highly desirable that these materials exhibit excellent space radiation exposure mitigation properties for protection of both the crew and onboard sensitive electronics systems. In this paper, we present trapped electron and proton space radiation exposure computational results for a variety of materials and shielding thicknesses for several earth orbit scenarios that include 1) low earth orbit (LEO), 2) medium earth orbit (MEO), and 3) geostationary orbit (GEO). We also present space radiation exposure (galactic cosmic radiation and solar particle event) results as a function of selected materials and thicknesses.

In an earlier paper, we presented space radiation exposure estimates to male astronauts using the Computerized Anatomical Male (CAM) model. In this paper, the Computerized Anatomical Female (CAF) model was utilized to calculate the space radiation exposure estimates to female astronauts for several altitudes ranging from 375 km to 450 km at an orbital inclination of 51.6 deg for both solar minimum and solar maximum conditions. Astronauts in space will be exposed to the trapped (Van Allen) proton and electron environment as well as the naturally occurring background galactic cosmic radiation and possibly high-energy solar particles emitted during periods of increased solar activity. Using a radiation shielding model of the International Space Station (ISS), shielding distributions were generated for a number of locations in the habitable ISS modules.

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.

Estimates of the effectiveness of the high-hydrogen containing materials, sodium alanate and ammonia borane, are made by calculating dose and dose equivalent for the 1977 solar minimum and 1970 solar maximum galactic cosmic ray spectra and for the large solar particle event spectra from the space era event of August 1972 and comparing their shielding effectiveness with that of polyethylene.

A Rando™ human phantom torso experiment is scheduled to fly on the International Space Station (ISS) mounted on and external to the Service Module in 2004 to simulate astronaut/cosmonaut extravehicular activity (EVA) space radiation exposures at various locations in the human body. The experiment will also contain the DLR/University of Kiel DOSTEL solid-state detector, the NASA Goddard Space Flight Center radiation effects experiment, and a NASA Johnson Space Center Tissue Equivalent Proportional Counter. In this paper the Matroshka experiment and scientific objectives are discussed in detail with the primary focus on the anticipated human body organ exposures from the space radiation environment. Preflight space radiation exposure calculations are presented for a number of locations in and on the human phantom torso using models of the trapped particle and galactic cosmic radiation environments.

Protecting astronauts from space radiation exposure is an important challenge for mission design and operations for future exploration-class and long-duration missions. Crew members are exposed to sporadic solar particle events (SPEs) as well as to the continuous galactic cosmic radiation (GCR). If sufficient protection is not provided the radiation risk to crew members from SPEs could be significant. To improve exposure risk estimates and radiation protection from SPEs, detailed evaluations of radiation shielding properties are required. A model using a modern CAD tool ProE™, which is the leading engineering design platform at NASA, has been developed for this purpose. For the calculation of radiation exposure at a specific site, the cosine distribution was implemented to replicate the omnidirectional characteristic of the 4π particle flux on a surface.

The space radiation environment consists of geomagnetically trapped protons and electrons, galactic cosmic radiation, and at times, high-energy solar particles that can penetrate spacecraft and spacesuits to produce a significant radiation exposure to crewmembers. The International Space Station (ISS) era will find astronauts spending months at a time on orbit, will occur during the rise and peak of the current solar cycle, and the construction of the ISS will require astronauts to perform these tasks in thinly shielded spacesuits. In order to determine the astronaut radiation exposures and related health risks, computerized anatomical male and female models have been developed and are used in conjunction with models of the space radiation environment and spacecraft and spacesuit shielding models. The National Council on Radiation Protection and Measurements (NCRP) has identified several critical body organs that are at risk.

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.

Space Shuttle astronauts are exposed to both the “trapped” radiation and the galactic cosmic radiation environments. In addition, the sun periodically emits high-energy particles which could pose a serious threat to flight crews. NASA adheres to federal regulations and recommended exposure limits for radiation protection and has established a radiological health and risk assessment program. Using models of the space radiation environment, a Shuttle shielding model, and an anatomical human model, crew exposure estimates are made for each Shuttle flight. The various models are reviewed. Dosimeters are worn by each astronaut and are flown at several fixed locations to obtain in-flight measurements. The dosimetry complement is discussed in detail. A comparison between the premission calculations and measurements is presented. Extrapolation of Shuttle experience to long-duration exposure us explored.

Most trapped proton effects studies assume a particle omni-directionality, while in reality the trapped particle environment is highly directional. This effect, called the “East-West effect,” has been observed and measured on several Space Shuttle missions. Normally one assumes that the Shuttle flies at different attitudes during the course of the mission and the directionality effects get “smeared out.” The International Space Station (ISS), however, will fly at a fixed attitude. Using the SPENVIS on-line capability and the anisotropic proton models of Badhwar-Konradi (B-K) and Watts (Vector Flux model: VF1), trapped proton differential spectra were generated for selected altitudes (51.6 deg inclination) for both solar minimum and maximum. Incorporating a particle transport code and a shielding model of the ISS, transmitted proton spectra can be computed as a function of shield thickness and polar and azimuthal angles (“look direction”) for ISS habitable modules.

Solar proton events (SPEs) represent the single-most significant source of acute radiation exposure during space missions. Historically, an exponential in rigidity (particle momentum) fit has been used to express the SPE energy spectrum using GOES data up to 100 MeV. More recently, researchers have found that a Weibull fit better represents the energy spectrum up to 1000 MeV (1 GeV). In addition, the availability of SPE data extending up to several GeV has been incorporated in analyses to obtain a more complete and accurate energy spectrum representation. In this paper we discuss the major SPEs that have occurred over the past five solar cycles (~50+ years) in detail - in particular, Aug 1972 and Sept & Oct 1989 SPEs. Using a high-energy particle transport/dose code, radiation exposure estimates are presented for various thicknesses of aluminum. The effects on humans and spacecraft systems are also discussed in detail.

Both humans and onboard radiosensitive systems (electronics, materials, payloads and experiments) are exposed to the deleterious effects of the harsh space radiations found in the space environment. The purpose of this paper is to present the space radiation environment extended to deep space based on environment models for the moon, Mars, Jupiter, and Saturn and compare these radiation environments with the earth's radiation environment, which is used as a comparative baseline. The space radiation environment consists of high-energy protons and electrons that are magnetically “trapped” in planetary bodies that have an intrinsic magnetic field; this is the case for earth, Jupiter, and Saturn (the moon and Mars do not have a magnetic field). For the earth this region is called the “Van Allen belts,” and models of both the trapped protons (AP-8 model) and electrons (AE-8 model) have been developed.