Abstract

Radiation Protection at Earths Orbits and in Deep Space

Lembit Sihver

¹ NPI of the CAS, Prague, Czech Republic
² TU Wien, Vienna, Austria
³ Cosimic Shielding Corporation, Atlanta, GA, USA

lembit.sihver@tuwien.ac.at
 

Abstract

To enable the planned rapid growth of both government and private operators in space, including satellites, space tourism and manned missions to the Moon and to Mars, a realistic and holistic approach to radiation risk reduction is needed. At orbits close to Earths, the main parts of the ionizing radiation come from trapped particles. In deep space, radiation from Galactic Cosmic Rays (GCRs) and Solar Energetic Particles (SEPs) from the sun pose a critical threat to both humans and electronic equipment. GCRs provide a chronic, slowly varying, highly energetic background source of High-Z and high-Energy (HZE) particles, while the Sun's activity varies with an 11-year cycle during which the Sun produces Solar Wind (SW) at varying intensities and unpredictable bursts of SEPs. For successful missions, it is therefore very important to be able to apply the best possible radiation protection. Currently, the only proven and practical countermeasure to reduce the exposure to GCRs and SEPs is passive shielding. However, the currently used metal shielding can increase the damage to humans and electronic behind the shielding.

It is well known that low atomic number (Z) materials are most effective for shielding in space, and liquid hydrogen has the maximum theoretical performance as shield material. Hydrogen is however not a practical shield material, being a low temperature liquid associated with practical handling problems and explosion risks. Hydrogen concentrated in polymer-based composites, however, is ideal for stopping primary cosmic and solar radiation and slow fast secondary neutrons created when the HZE particles are impinging on the spacecraft. Addition of nuclides with different high capture cross sections increases the protection against different secondary particles present. By modifying the fiber/pore size and polymer chain orientation, the polymer materials can also be engineered to act as either efficient heat insulators or efficient heat conductors, providing a broad range of thermoregulation functionalities without compromising the ionizing radiation shielding properties. Polymers are also very suitable for space suits and other protection garments.The fundamental advantages of using polymers for multifunctional shielding purposes will be presented.