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Long-term exposure to the space radiation environment poses deleterious effects to both humans and space systems. The major sources of the radiation effects come from high energy galactic cosmic radiation and solar proton events. In this paper we investigate the radiation-mitigation properties of several shielding materials for possible use in spacecraft design, surface habitats, surface rovers, spacesuits, and temporary shelters. A discussion of the space radiation environment is presented in detail. Parametric radiation shielding analyses are presented using the NASA HZETRN 2005 code and are compared with ground-based experimental test results using the Loma Linda University Proton Therapy facility.

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.

Space radiation exposure limits for astronauts are based on recommendations of the National Council on Radiation Protection and Measurements. These limits now include the age at exposure and sex of the astronaut. A recently-developed computerized anatomical female (CAF) model is discussed in detail. Computer-generated, cross-sectional data are presented to illustrate the completeness of the CAF model. By applying ray-tracing techniques, shield distribution functions have been computed to calculate absorbed dose and dose equivalent values for a variety of critical body organs (e.g., breasts, lungs, thyroid gland, etc) and mission scenarios. Specific risk assessments, i.e., cancer induction and mortality, are reviewed.

AFR, Inc. is developing a multifunctional Carbon material that, in addition to excellent radiation shielding characteristics, is appropriate for certain energy storage applications. As an excellent Hydrogen gas sorbent, it increases the usable storage capacity of a gas cylinder by ∼25% at 3500 PSI and by ∼150% at 500 PSI. Our ongoing NASA Langley funded study shows that when a sorbent-filled tank is charged with hydrogen, it provides shielding superior to polyethylene against most types of ionizing particles. Even as hydrogen is consumed, the carbon and tank ensure that significant radiation shielding capability is maintained. In addition to storing hydrogen, the carbon material also displays considerable strength. In this paper, we explore some of its mechanical properties that show this material is very versatile and highly multifunctional.

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.

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.

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.

Special exposure limit recommendations have been designated by the National Council on Radiation Protection (NCRP) for U. S. astronauts in low earth orbit (LEO) operations. These have been established from consideration of a 3% lifetime excess risk of cancer mortality for a 10-yr. active career. The most recent recommendations of the National Council on Radiation Protection and Measurements (NCRP) have incorporated modified procedures for evaluating exposures with accompanying adjustments in career limits. Of special importance are the limit specifications for female exposures, which are approximately 40% less than those for males. Furthermore, radiosensitive organs unique to females require additional attention.

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.

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.

The bulk of the daily space radiation exposure to International Space Station astronauts will be received during times spent at selected locations. Using a recently updated and improved shielding model of the ISS, mass shielding distributions have been generated for these selected ISS locations. Anatomical math models have been developed for use in conjunction with spacecraft shielding models and space radiation dose codes to compute astronaut radiation exposures at the critical body organ level. In this paper we present a parametric study of crew radiation exposures at several selected locations, discuss the impact and effects on several mission scenarios, and present some ideas to further mitigate their exposures.

A human phantom torso experiment (PTE) has flown in space twice: once on Space Shuttle mission STS-91 (June 1998), and once on the International Space Station (ISS) (mid 2001). During these flights active and passive radiation dosimeters recorded space radiation exposures to five critical body organs (brain, thyroid, heart/lung, stomach, and colon) and to several surface (skin) locations. There are also plans to fly the PTE during the ISS 12A.1 mission with the Increment 8 crew (2003) and to fly a similar phantom torso experiment, called “Matroshka,” which will be mounted external to and on the ISS Service Module (2004). Recently, there has been interest expressed within the radiation biology community for measurements at specific red (and yellow) bone marrow sites in the human body. Current plans are to repeat the above organ site measurements, but also take space radiation measurements at several selected bone marrow sites in the forthcoming PTE and Matroshka flights.

AFR, Inc. is developing a multifunctional Carbon material that, in addition to excellent radiation shielding characteristics, is appropriate for certain energy storage applications. As an excellent Hydrogen gas sorbent, it increases the usable storage capacity of a gas cylinder by ∼25% at 3500 PSI and by ∼150% at 500 PSI. Our ongoing NASA Langley funded study shows that when a sorbent-filled tank is charged with hydrogen, it provides shielding superior to polyethylene against most types of ionizing particles. Even as hydrogen is consumed, the carbon and tank ensure that significant radiation shielding capability is maintained. Vastly improved radiation shielding is a clear requirement for a potential manned mission to Mars or a long-duration base on the surface of the Moon. However, current shielding technologies are predicated upon systems dedicated solely to the task of shielding.

One of the risks associated with long-term space flights is cancer incidence resulting from chronic exposure to space radiation. Assessment of incurred risk from radiation exposure requires quantifying the dose throughout the body. The space radiation exposure received by Space Shuttle astronauts is measured by thermoluminescent dosimeters (TLDs) worn during every mission. These dosimeters measure the absorbed dose to the skin, but the dose to internal organs is required for estimating the cancer risk induced by space radiation. A method to extrapolate these skin dose measurements to realistic organ specific dose estimates, using the Computerized Anatomical Man (CAM) and Computerized Anatomical Female (CAF) models, is discussed in detail. A transport code, which propagates high energy nucleon and charged particles, is combined with the CAM/CAF-generated shielding areal distributions to evaluate the absorbed dose at selected organ sites.

This paper presents a general review and current support efforts in space radiation analysis and dosimetry at the NASA Johnson Space Center. Dating back to the Mercury program of the 1960's, radiation dosimeters have been worn by flight crews on every US space mission to measure and monitor the natural space radiation environment. Topics discussed include the space radiation environment, analytical spacecraft and anatomical modelling techniques, radiation dose programs, mission support functions and objectives, flight instrumentation, and measurements. Federal regulations for radiation protection and Space Shuttle astronaut dose limits are reviewed. The Shuttle mission operations support is discussed in detail, which includes pre-mission dose exposure computations, real-time Shuttle support activities, and post-flight analyses.

Space radiation measurements were made on the International Space Station (ISS) with the Bulgarian Liulin-E094 Mobile Dosimetry Units (MDU) during 2001. The Liulin-E094 was part of the Dosimetric Mapping experiment lead by Dr. G. Reitz, DLR. Four MDUs were placed at fixed locations: one unit in the ISS “Unity” Node-1 and three units were located in the US Laboratory module. Space radiation flight measurements were obtained during the time period May 11 – July 26, 2001. In this paper we discuss the development of an MDU shielding model using combinatorial geometry and 3-D visualization and the orientation and placement at the four locations within the ISS. Four shielding distributions were generated for the combined ISS and MDU shielding models. The AP8MAX trapped proton model was used to compute the daily absorbed dose for the four MDUs and are compared with the flight measurements.

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.

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 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 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.