Determination of total ionization dose by ray trace analysis based on a geodesic sphere

When designing the spacecraft, it is necessary to take into account the deleterious action of various factors in outer space. The main factor limiting active life of spacecraft is ionization radiation and it is the cause of most failures. Its influence is accompanied by ionization losses of the energy of charged particles in active and passive areas of semi- conductors and integrated circuits; that leads to emergence of radiation effects and it is characterized by the value of absorbed dose. At present there are several approaches to forecast the value of total ionization dose (TID): Monte- Carlo methods, methods that take into account only standard shield geometry (sphere, plane) and ray trace analysis (or sector-based analysis). The paper presents a modification of ray trace analysis that uses a geodesic sphere for sector construction and pro- vides regularly distribution of tracing rays in space unlike classical approach with using a parametrical representation of a sphere. Our approach enables to take into consideration real density of materials and allows using fewer sectors to meet the requirements of the method 154.PM-129 and keeping calculation accuracy. This is especially important for carrying out element-by-element radiation analysis taking into account heterogeneous protection through shielding of calculated point by elements of spacecraft design. This method is implemented as an extension for SolidWorks CAD. The input data for calculation are the following: 3d-model of equipment component as a part of spacecraft and radiation attenuation tables. The accuracy and the speed of the analysis depends on the number of tracing rays, and it is possible to carry out the calculation for several types of ionizing radiation at the same time. As an example of using the proposed method and a software module, we carried out radiation analysis of the block of the on-board digital computer for the spacecraft “Sfera”; its active life duration is 10 years on a high-elliptic orbit and 15 years on a geostationary orbit. As a result, we revealed that for the elements of the block minimum and maxi- mum total ionization doses differed substantially. It means that taking into account shielding properties of structural elements of device and blocks makes significant contribution to TID calculation.