Radiation Shielding of Composite Space Enclosures

… SOCIETÀ ITALIANA DI …, 2008

The SPADA (SPAce Dosimetry for Astronauts) project is a part of an extensive teamwork that aims to optimize shielding solutions against space radiation. Shielding is indeed an irreplaceable tool to reduce exposure of crews of future Moon and Mars missions. We concentrated our studies on two flexible materials, Kevlar R and Nextel R , because of their ability to protect human space infrastructures from micrometeoroids. We measured radiation hardness of these shielding materials and compared to polyethylene, generally acknowledged as the most effective space radiation shield with practical applications in spacecraft. Both flight test (on the International Space Station and on the Russian FOTON M3 rocket), with passive dosimeters and accelerator-based experiments have been performed. Accelerator tests using high-energy Fe ions have demonstrated that Kevlar is almost as effective as polyethylene in shielding heavy ions, while Nextel is a poor shield against high-charge and -energy particles. Preliminary results from spaceflight, however, show that for the radiation environment in low-Earth orbit, dominated by trapped protons, thin shields of Kevlar and Nextel provide limited reduction.

2015

The NASA Langley Research Center Shields CubeSat initiative is to develop a configurable platform that would allow lower cost access to Space for materials durability experiments, and to foster a pathway for both emerging and commercial-off-the-shelf (COTS) radiation shielding technologies to gain spaceflight heritage in a relevant environment. The Shields-1 will be Langley's first CubeSat platform to carry out this mission. Radiation shielding tests on Shields-1 are planned for the expected severe radiation environment in a geotransfer orbit (GTO), where advertised commercial rideshare opportunities and CubeSat missions exist, such as Exploration Mission 1 (EM-1). To meet this objective, atomic number (Z) graded radiation shields (Z-shields) have been developed. The Z-shield properties have been estimated, using The Space Environment Information System (SPENVIS) radiation shielding computational modeling, to have ~30% increased shielding effectiveness for electrons, at half the thickness of a corresponding single layer of aluminum. The Shields-1 research payload will be made with Z-graded radiation shields of varying thicknesses to create dose-depth curves to be compared with baseline materials. Additionally, Shields-1 demonstrates an engineered Z-grade radiation shielding vault protecting the system's electronic boards. The radiation shielding materials' performances will be characterized using total ionizing dose sensors. Completion of these experiments is expected to raise the technology readiness levels (TRLs) of the tested Z-graded materials. The most significant contribution of the Z-shields for the SmallSat community is that it enables cost effective shielding for small satellite systems, with significant volume constraints, while increasing the operational lifetime of ionizing radiation sensitive components. These results are anticipated to increase the development of CubeSat hardware design for increased mission lifetimes, and enable out of low earth orbit (LEO) missions by using these tested material concepts as shielding for sensitive components and new spaceflight hardware.

This report describes the research completed during 2011 for the NASA Innovative Advanced Concepts (NIAC) project. The research is motivated by the desire to safely send humans in deep space missions and to keep radiation exposures within permitted limits. To this end current material shielding, developed for low earth orbit missions, is not a viable option due to payload and cost penalties. The active radiation shielding is the path forward for such missions. To achieve active space radiation shielding innovative large lightweight gossamer space structures are used. The goal is to deflect enough positive ions without attracting negatively charged plasma and to investigate if a charged Gossamer structure can perform charge deflections without significant structural instabilities occurring. In this study different innovative configurations are explored to design an optimum active shielding. In addition, to establish technological feasibility experiments are performed with up to 10kV of membrane charging, and an electron flux source with up to 5keV of energy and 5mA of current. While these charge flux energy levels are much less than those encountered in space, the fundamental coupled interaction of charged Gossamer structures with the ambient charge flux can be experimentally investigated. Of interest are, will the EIMS remain inflated during the charge deflections, and are there visible charge flux interactions. Aluminum coated Mylar membrane prototype structures are created to test their inflation capability using electrostatic charging. To simulate the charge flux, a 5keV electron emitter is utilized. The remaining charge flux at the end of the test chamber is measured with a Faraday cup mounted on a movable boom. A range of experiments with this electron emitter and detector were performed within a 30x60cm vacuum chamber with vacuum environment capability of 10 -7 Torr. Experiments are performed with the charge flux aimed at the electrostatically inflated membrane structure (EIMS) in both charged and uncharged configurations. The amount of charge shielding behind and around the EIMS was studied for different combinations of membrane structure voltages and electron energies. Both passive and active shielding were observed, with active shielding capable of deflecting nearly all incoming electrons. The pattern of charge distribution around the structure was studied as well as the stability of the structures in the charge flow. The charge deflection experiments illustrate that the EIMS remain inflated during charge deflection, but will experience small amplitude oscillations. Investigations were performed to determine a potential cause of the vibrations. It is postulated these vibrations are due to the charge flux causing local membrane charge distribution changes. As the membrane structure inflation pressure is changed, the shape responds, and causes the observed sustained vibration. Having identified this phenomenon is important when considering electrostatically inflated membrane structures (EIMS) in a space environment. Additionally, this project included a study of membrane material impacts, specifically the impact of membrane thickness. Extremely thin materials presented new challenges with vacuum preparation techniques and rapid charging. The thinner and lighter membrane materials were successfully inflated using electrostatic forces in a vacuum chamber. However, care must be taken when varying the potentials of such lighter structures as the currents can cause local heating and melting of the very thin membranes. Lastly, a preliminary analysis is performed to study rough order of magnitude power requirements for using EIMS for radiation shielding. The EIMS power requirement becomes increasingly more challenging as the spacecraft voltage is increased. As a result, the emphasis is on the deflection of charges away from the spacecraft rather than totally stopping them. This significantly alleviates the initial power requirements. With modest technological development(s) active shielding is emerging to be a viable option.

1999

The potential for serious health risks from solar particle events (SPE) and galactic cosmic rays (GCR) is a critical issue in the NASA strategic plan for the Human Exploration and Development of Space (HEDS). The excess cost to protect against the GCR and SPE due to current uncertainties in radiation transmission properties and cancer biology could be exceedingly large based on the excess launch costs to shield against uncertainties. The development of advanced shielding concepts is an important risk mitigation area with the potential to significantly reduce risk below conventional mission designs. A key issue in spacecraft material selection is the understanding of nuclear reactions on the transmission properties of materials. High-energy nuclear particles undergo nuclear reactions in passing through materials and tissue altering their composition and producing new radiation types. Spacecraft and planetary habitat designers can utilize radiation transport codes to identify optimal materials for lowering exposures and to optimize spacecraft design to reduce astronaut exposures. To reach these objectives will require providing design engineers with accurate data bases and computationally efficient software for describing the transmission properties of space radiation in materials. Our program will reduce the uncertainty in the transmission properties of space radiation by improving the theoretical description of nuclear reactions and radiation transport, and provide accurate physical descriptions of the track structure of microscopic energy deposition.

2007

We report the space radiation shielding benefits achieved by replacing conventional spacecraft structural materials, e.g. aluminum, with lower average atomic number materials in an enhanced Cygnus Pressurized Cargo Module (PCM), a candidate for the NASA Exploration Augmentation Module (EAM). Increased shielding effectiveness at constant spacecraft mass, as well as possible weight savings at constant dose, are demonstrated. The principal space radiation environment examined here is the solar particle event (SPE) environment outside Earth's magnetosphere.

2006 IEEE Aerospace Conference, 2006

IEEE Transactions on Nuclear Science, 1996

In this paper, we have pioneered a new direction concerning the shielding of electronic devices (at a microcircuit-packaging or a larger level) in a radiative environment. As a matter of fact, this work not only considers the role of the material itself on the shielding efficiency but also the effect of the structure of the shield. By simulations with the NOVICE we have explored the possibility of combining the specific attenuation properties of given materials in an optimized multilayer (and multimaterial) structure. This study is based on a brief theoretical overview of interaction of space radiation with material[31[4]. Then, the results of simulations are presented. The workfratne of these calculations is a worstcase geosynchronous orbit (160" West) for a period of 15 years (trapped electrons and protons from 4 anomalously large solar particle events). We found that it is possible to improve the shielding properties of a monomaterial absorber by using an optimized multilayer, multimaterial shield.

Radiation shielding is generally assumed to be a cost prohibitive means of mitigating radiation damage. This is true when considering any one of the main three methods of radiation shielding as a stand-alone system. However a synergistic design that utilizes the strong points of all methods, while reducing their weakness can be a cost-effective means of reducing the radiation threat. Radiation Shielding Overview The three main schools of thought on radiation shielding are Material, Magnetic and Electrostatic Shielding. Material Shielding requires a lot mass to be effective, which is a major drawback for space exploration. Material shielding protects against the greatest range of cosmic radiation. Magnetic Shielding has weak points at the poles, much like the Earth does, allowing radiation in at those spots. Most artificial magnetic field designs require a large power supply as well as complex wiring. Magnetic shielding works best against charged particles. Electrostatic Hull Shielding works by giving the hull a large electrostatic charge, which repels particles with the same charge, but attracts particles of the opposite charge. So electrostatic hull shielding can only protect against particles of a single charge, but is weak against particles of the opposite charge. Electrostatic systems however are low cost, simple designs with relatively small power requirements. Radiation Shielding Improvements for Spacecraft/Space Stations The solution is to combine the strengths of each of these methods, while reducing their drawbacks, in a single design. This can give us a reduction in mass and energy requirements over any stand-alone system. Lets start with electrostatic shielding and how it can be improved. Instead of applying a single charge to the entire ship, use both a positive and negatively charged region at the ends of the ship. The crew area in the middle of the ship should not have a charge. This will attract all charged particles away from the crew area.

1976

The computing software that was used to perform the charged particle radiation transport analysis and shielding design for the Mariner Jupiter/Saturn 1977 spacecraft is described. Electron fluences, energy spectra and dose rates obtained with this software are presented and compared with independent computer calculations.