Space Radiation Analysis Based On Geant4

Space radiation is a key parameter for orbital operations safety,and the analysis of space radiation is an indispensable part of space engineering.In this paper,we focus on atmospheric neutron simulation,spacecraft modeling and shielding analysis based on Geant4 toolkit.New space environment and radiation effect analysis tool is developed based on the commonly-used space environment and radiation effect models,which is verified by the radiation effect level analysis in all-electric propulsion transfer orbit.Firstly,based on the measured data and Geant4,the simulation of cosmic ray transport from outer boundary of the magnetosphere to 10-km altitude is completed,and the real-time calculation of atmospheric neutrons with 1-hour resolution is realized.Using Galactic Cosmic Ray Model-Bon14 and the various fitting functions of solar proton events,the real-time calculation of cosmic ray energy spectra is realized by using ACE/CRIS and GOES measured data,and compared with the measured data.Taking aim at low computational efficiency of geomagnetic cutoff,starting from the Lorentz equation of charged particles in magnetic field,using IGRF12 and Tsy05 geomagnetic field models,the modified MAGNETOCOSMICS is used to calculate the global geomagnetic cut-off at 100 km altitude.This paper develops a Geant4 based application for the propagation of protons and ? particles,which geometry model is established at intervals of 1 km using NLRMSISE-00 model.Using this application,the atmospheric neutron spectrum at aviation altitude caused by single energy particles and typical solar proton events is analyzed,and then an atmospheric neutron database is formed.Without considering the geomagnetic cut-off,the atmospheric neutron database was compared with similar models.The maximum error of total effective dose was 16.47% at the altitude of 10,20 and 60 km.Based on the above research,the real-time calculation of global atmospheric neutron energy spectrum and effective dose with 1 hour resolution is realized by interpolating inatmospheric neutron database and combining with fluence to effective dose conversion coefficients given by ICRP103 publication,which lays a foundation for radiation effect analysis in near space.Secondly,with the development of civil aerospace,space engineers urgently need to ensure the safe operation of spacecraft in orbit while reducing engineering costs.In this paper,the GDML language is used for modeling and extended according to the actual requirement.Considering the lack of data conversion between commercial CAD software such as Pro/Engineer,SolidWorks and Geant4,this paper uses open-source geometric modeling platform(Open Cascade)to load STEP files,tessellate solids into triangular mesh by Netgen Mesh Generator,then convert those mesh to GDML format.STEP-GDML Conversion can make up for the time-consuming and error-prone shortcomings of manually writing GDML,and support the establishment of complex geometric models.In order to meet the demand of three-dimensional Monte Carlo simulation of deep charging,this paper convert geometry into Elmer finite element mesh by Netgen,and realize the function of acquiring physical quantities in complex geometric structures which lays a good foundation for deep charging simulation.Based on FREECAD framework,the software for spacecraft modeling and shielding analysis with friendly user interface has been developed,which has the functions of creating simple geometry,import&export module,sector analysis module and calculating particle flux behind the shielding.Taking Laser Interferometer Space Antenna(LISA)as an example,the functions of the software are verified.The results show that the three-dimensional shielding analysis is more realistic than the one-dimensional model.It can be used to identify the weak shielding position,optimize the shielding protection and reduce the shielding weight.Finally,the latest radiation belt model Ap9Ae9 is compared with Ap8Ae8,which is commonly-used in engineering.In this paper,the energy spectra of radiation belt particles and dose shielded by 3mm aluminum in typical orbits,such as low earth orbit(LEO),solar synchronous orbit(SSO),geosynchronous transfer orbit(GTO),medium earth orbit(MEO)and geosynchronous orbit(GEO)are calculated by usingthe above two models.Based on the above results,some preliminary Guideline for selection of Ap9Ae9 model are given.In this paper,a Geant4 based application G4 Upset is developed to evaluate single event upsets using multi-sensitive volumes model.Taking AT60142 F SRAM as an example,the modeling of multi-sensitive volumes and the calculation process of on-orbit single event upset rate are introduced.According to the process of radiation effect Analysis,new space environment and radiation effect analysis tool is developed based on the commonly-used space environment and radiation effect model.Combined with the equivalent aluminum shielding thickness distribution calculated by Sector Analysis module,this tool can calculate space radiation environment,shielding energy spectrum,single event upset rate,total dose,displacement damage and solar cell damage.In addition to conventional radiation effect analysis,the latest Ap9-mean model is used to predict the anomaly of LEO satellites crossing South Atlantic Anomaly(SAA),which has served many satellites such as QUESS and DAMPE Satellite.The radiation level of all-electric propulsion satellite in transfer orbit is calculated by using radiation effect evaluation software.The results show that the single event effects and solar cell damage in All-electric propulsion satellite are very serious because of a prolonged time spent within the radiation belts,and need special attention.