Modelling of protons spectra encountered in space using medical accelerator and its microdosimetric characterization

Radiation environments in space are mainly composed of protons coming from the Galactic Cosmic Rays (GCRs) pervading the universe, the Solar Particle Events (SPEs) resulting from solar flares and coronal mass ejections, and the two Van Allen Belts surrounding the Earth due to the presence of the geomagnetic field trapping charged particles. Their wide spectra of energies up to hundreds of GeV imply diverse radiobiological effects to astronauts and radiation damage to electronics in the spacecraft. Even if lower in abundance, heavy ions such as He, C, O, Si, Fe are present in space and constitute an even bigger hazard due to their high penetrability and high linear energy transfer (LET). Most irradiation facilities available for research and testing worldwide provide usually only monoenergetic beams of high-energy protons or other heavier particles limiting studies of radiobiological effects and effects on electronics to a set of discrete energies.This paper introduces a procedure where a proton fluence spectra of interest for space radiation protection, previously generated by Monte Carlo simulations was delivered using a clinical proton therapy accelerator. Particularly, it reports the first results of modelling a proton radiation field in space in the energy range from 70 to 230 MeV during a single experimental session by programming a treatment planning system (TPS) to deliver required proton irradiation energies. Moreover, the angular distribution of the proton irradiation field has been varied to reproduce the isotropic exposure experienced by humans in space. The obtained proton radiation field was characterized using a 3D sensitive volume SOI microdosimeter developed by the Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia.     

Countermeasures for space radiation induced adverse biologic effects

Radiation exposure in space is expected to increase the risk of cancer and other adverse biological effects in astronauts. The types of space radiation of particular concern for astronaut health are protons and heavy ions known as high atomic number and high energy (HZE) particles. Recent studies have indicated that carcinogenesis induced by protons and HZE particles may be modifiable. We have been evaluating the effects of proton and HZE particle radiation in cultured human cells and animals for nearly a decade. Our results indicate that exposure to proton and HZE particle radiation increases oxidative stress, cytotoxicity, cataract development and malignant transformation in in vivo and/or in vitro experimental systems. We have also shown that these adverse biological effects can be prevented, at least partially, by treatment with antioxidants and some dietary supplements that are readily available and have favorable safety profiles. Some of the antioxidants and dietary supplements are effective in preventing radiation induced malignant transformation in vitro even when applied several days after the radiation exposure. Our recent progress is reviewed and discussed in the context of the relevant literature.     

K6R4016V1D芯片在低地球轨道发生单粒子效应频次的分析

俄罗斯福布斯-土壤火星探测器于2011年11月9日携带中国首个火星探测器萤火一号进入低地球轨道(LEO),但原定于159min后探测器在轨发动机点火变轨未能实施,最终探测计划失败.俄罗斯航天局研究分析认为,事故最可能是由于宇宙线重离子轰击星载计算机存储器件,导致两台计算机重启所致.但是抗辐射专家对空间辐射粒子会在如此短时间内通过单粒子效应(SEE)导致LEO探测器失效的观点并不认同.本文根据俄罗斯航天局发布的受影响器件信息,通过实验和计算,分析了K6R4016V1D芯片在低地球轨道运行时可能遇到的空间辐射粒子诱发单粒子效应的频次,探讨了单粒子效应导致福布斯-土壤火星探测器失效的可能性.      

航空电子设备NSEE试验评价方法

本文定义了航空电子设备大气中子单粒子效应(NSEE)硬失效、硬错误与软错误等大气中子辐射可靠性表征参数,提出了一套航空电子设备抗大气中子单粒子效应危害能力的试验评价方法,包括试验应力终止条件与起始条件的确定方法、M_NSEE预估方法、试验程序、试验评价方法等,并通过某航空用卫星导航接收机试验案例证明了该方法在工程应用中的可操作性与有效性,通过掌握数字信号处理(DSP)、静态随机存储器(SRAM)、现场可编程门阵列(FPGA)的NSEE敏感特性,可为航空用卫星导航接收机NSEE危害防控提供针对性的技术支持.本文为我国航空电子产品大气中子单粒子效应试验评价奠定了理论与应用基础,同时也为其他电子信息产品在大气中子单粒子效应试验评价方面提供了重要依据和参考.      

The effects of proton radiation on UHMWPE material properties for space flight and medical applications

Ultra High Molecular Weight Polyethylene (UHMWPE) is a polymer widely used as a radiation shielding material in space flight applications and as a bearing material in total joint replacements. As a long chain hydrocarbon based polymer, UHMWPE’s material properties are influenced by radiation exposure, and prior studies show that gamma irradiation is effective for both medical sterilization and increased wear resistance in total joint replacement applications. However, the effects of space flight radiation types and doses on UHMWPE material properties are poorly understood. In this study, three clinically relevant grades of UHMWPE (GUR 1020, GUR 1050, and GUR 1020 blended with Vitamin E) were proton irradiated and tested for differences in material properties. Each of the three types of UHMWPE was irradiated at nominal doses of 0 Gy (control), 5 Gy, 10 Gy, 20 Gy, and 35 Gy. Following irradiation, uniaxial tensile testing and thermal testing using Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) were performed. Results show small but significant changes in several material properties between the control (0 Gy) and 35 Gy samples, indicating that proton irradiation could have a effect on the long term performance of UHMWPE in both medical and space flight applications.     

Space weather and commercial airlines

Space weather phenomena can effect many areas of commercial airline operations including avionics, communications and GPS navigation systems. Of particular importance at present is the recently introduced EU legislation requiring the monitoring of aircrew radiation exposure, including any variations at aircraft altitudes due to solar activity. With the introduction of new ultra-long-haul “over-the-pole” routes, “more-electric” aircraft in the future, and the increasing use of satellites in the operation, the need for a better understanding of the space weather impacts on future airline operations becomes all the more compelling. This paper will present the various space weather effects, some provisional results of an ongoing 3-year study to monitor cosmic radiation in aircraft, and conclude by summarising some of the identified key operational issues, which must be addressed, with the help of the science community, if the airlines want to benefit from the availability of space weather services.     

Space weather in Japan

In Japan, Communications Research Laboratory engages in operational space environment information services as National Forecasting Center and Regional Warning Center of ISES. Data from local observations and data collected via internet from domestic and foreign institutes are used for the daily operational forecast. Fundamental research on space weather issues has been carried out at several institutes and universities, including STE Laboratory and NASDA. In this presentation, an overview of current space weather forecast operations and a system for information outreach in Japan will be presented. Current and future observation programs from ground-base and space will be also briefly reviewed.     

Onboard orbit determination using GPS observations based on the unscented Kalman filter

Spaceborne GPS receivers are used for real-time navigation by most low Earth orbit (LEO) satellites. In general, the position and velocity accuracy of GPS navigation solutions without a dynamic filter are 25 m (1σ) and 0.5 m/s (1σ), respectively. However, GPS navigation solutions, which consist of position, velocity, and GPS receiver clock bias, have many abnormal excursions from the normal error range for space operation. These excursions lessen the accuracy of attitude control and onboard time synchronization. In this research, a new onboard orbit determination algorithm designed with the unscented Kalman filter (UKF) was developed to improve the performance. Because the UKF is able to obtain the posterior mean and covariance accurately by using the second-order Taylor series expansion through the sampled sigma points that are propagated by using the true nonlinear system, its performance can be better than that of the extended Kalman filter (EKF), which uses the linearized state transition matrix to predict the covariance. The dynamic models for orbit propagation applied perturbations due to the 40 × 40 geo-potential, the gravity of the Sun and Moon, solar radiation pressure, and atmospheric drag. The 7(8)th-order Runge–Kutta numerical integration was applied for orbit propagation. Two types of observations, navigation solutions and C/A code pseudorange, can be used at the user’s discretion. The performances of the onboard orbit determination were verified using real GPS data of the CHAMP and KOMPSAT-2 satellites. The results of the orbit determination were compared with the precision orbit ephemeris (POE) of the CHAMP and KOMPSAT-2 satellites.     

Design of BDS-3 integrity monitoring and preliminary analysis of its performance

With the improvement in the service accuracy and expansion of the application scope of satellite navigation systems, users now have high demands for system integrity that are directly related to navigation safety. As a crucial index to measure the reliability of satellite navigation systems, integrity is the ability of the system to send an alarm when an abnormity occurs. The new-generation Beidou Navigation Satellite System (BDS-3) prioritized the upgrading of system integrity as an important objective in system construction. Because the system provides both basic navigation and satellite-based augmentation system (SBAS) services by the operational control system, BDS-3 adopts an integrated integrity monitoring and processing strategy that applies satellite autonomous integrity monitoring and ground-based integrity monitoring for both the basic navigation service and SBAS navigation service. BDS-3 also uses an improved and refined integrity parameter system to provide slow, fast and real-time integrity parameters for basic navigation, and provide SBAS-provided integrity information messages in accordance with Radio Technical Commission for Aeronautics (RTCA) specification and dual frequency, multi-constellation (DFMC) specification to support the SBAS signal frequency, single constellation operation and DFMC operation respectively. The performance of BDS-3 system integrity monitoring is preliminarily verified during on-orbit testing in different states, including normal operation, satellite clock failure and satellite ephemeris failure. The results show that satellite autonomous integrity monitoring, ground-based integrity monitoring and satellite-based augmentation all correctly work within the system. Satellite autonomous integrity monitoring can detect satellite clock failure but not satellite orbit failure. However, ground-based integrity monitoring can detect both. Moreover, the satellite-based augmentation integrity system monitors the differential range error after satellite ephemeris and clock error corrections based on user requirements. Compared to the near minute-level time-to-alert capability of ground-based integrity monitoring, satellite autonomous integrity monitoring reduces the system alert time to less than 4 s. With a combined satellite-ground monitoring strategy and the implementation of different monitoring technologies, the BDS-3 integrity of service has been considerably improved.     

Design and experiment of onboard laser time transfer in Chinese Beidou navigation satellites

High-precision time synchronization between satellites and ground stations plays the vital role in satellite navigation system. Laser time transfer (LTT) technology is widely recognized as the highest accuracy way to achieve time synchronization derived from satellite laser ranging (SLR) technology. Onboard LTT payload has been designed and developed by Shanghai Astronomical Observatory, and successfully applied to Chinese Beidou navigation satellites. By using the SLR system, with strictly controlling laser firing time and developing LTT data processing system on ground, the high precise onboard laser time transfer experiment has been first performed for satellite navigation system in the world. The clock difference and relative frequency difference between the ground hydrogen maser and space rubidium clocks have been obtained, with the precision of approximately 300 ps and relative frequency stability of 10E−14. This article describes the development of onboard LTT payload, introduces the principle, system composition, applications and LTT measuring results for Chinese satellite navigation system.     

移位损伤剂量模型及其应用

首先描述了移位损伤的机理及其影响器件性能的机制,引入了适合航天器工程抗辐射加固设计使用的移位损伤剂量模型,探讨了其在CCD器件电荷传输效率CTE,Si器件平均暗电流以太阳电池阵输出功率等工程参数衰降中的应用,介绍了建立的基于移位损伤剂量模型的空间环境中CCD器件CTE衰降预测模式,其结果与欧空局空间环境信息系统的计算结果相吻合．该程序在光电器件抗辐射加固设计中具有重要的应用价值．     

一种平面约束辅助测量的深空探测器自主天文导航方法

深空探测任务中自主导航测量误差是影响深空探测自主导航系统精度的主要影响因素。针对抑制自主导航测量误差的问题,提出一种平面约束辅助测量的深空探测器自主天文导航方法,该方法在对系统非线性不等式几何平面约束建模的基础上,利用序列二次规划(Sequential Quadratic Programming,SQP)非线性规划方法,对深空探测器自主天文导航系统的非线性不等式约束进行非线性规划,直接辅助减小深空探测器自主导航系统的量测误差;利用CKF-SQP量测优化非线性约束滤波方法,对深空探测器自主导航系统的状态进行估计,进一步减小系统随机误差。仿真结果表明:所提方法可以有效抑制测量误差,实现深空探测器高精度自主导航。该方法可为深空探测器提供一种可行的高精度自主导航方法。     

Analysis of BDS-3 distributed autonomous navigation based on BeiDou system simulation platform

Satellite autonomous navigation is an important function of the BeiDou-3 navigation System (BDS-3). Satellite autonomous navigation means that the navigation satellite uses long-term forecast ephemeris and Inter-Satellite Link (ISL) measurements to determinate its own spatial position and time reference without the support of the ground Operation and Control System (OCS) for a long time to ensure that the navigation system can normally maintain the time and space reference. This paper aims to analyze the feasibility of distributed autonomous navigation algorithms. For the first time, a ground parallel autonomous navigation test system (GPANTS) is built. The performance of distributed autonomous navigation is then analyzed using the two-way ISL ranging of BDS-3 satellites. First, the BDS simulation platform and the GPANTS are introduced. Then, the basic principles of distributed satellite autonomous orbit determination and time synchronization based on ISL measurements are summarized. Preliminary evaluation of the performance of the BDS-3 constellation autonomous navigation service under ideal conditions through simulation data. Then the performance of autonomous navigation for 22 BeiDou-3 satellites using ISL measurements is evaluated. The results show that when satellites operate autonomously for 50 days without the support of any ground station, the User Range Error (URE) of autonomous orbit determination is better than 3 m, and the time synchronization accuracy is better than 4 ns.     

Animal studies of life shortening and cancer risk from space radiation.

The U.S. Air Force study of the delayed effects of single, total body exposures to simulated space radiation in rhesus monkeys is now in its 21st year. Observations on 301 irradiated and 57 age-matched control animals indicate that life expectancy loss from exposure to protons in the energy range encountered in the Van Allen belts and solar proton events can be expressed as a logarithmic function of the dose. The primary causes of life shortening are cancer and endometriosis (an abnormal proliferation of the lining of the uterus in females). Life shortening estimates permit comparison of the risk associated with space radiation exposures to be compared with that of other occupational and environmental hazards, thereby facilitating risk/benefit decisions in the planning and operational phases of manned space missions. Calculations of the relative risk of fatal cancers in the irradiated subjects reveal that the total body surface dose required to double the risk of death from cancer over a 20-year post exposure period varies with the linear energy transfer (LET) of the radiation. The ability to determine the integrated dose and LET spectrum in space radiation exposures of humans is, therefore, critical to the assessment of lifetime cancer risk.     

基于稀疏表示和字典学习的地磁基准图构建方法

地磁匹配导航在导航制导领域具有重要作用，地磁基准图的构建精度决定了地磁匹配导航的有效性。针对现有地磁基准图构建精度难以满足实际应用需求的问题，提出了基于稀疏表示和字典学习的高精度地磁基准图构建方法。首先，利用矩谐分析(RHA)进行稀疏字典的初始化；其次，利用K-SVD算法对稀疏字典进行训练；最后，利用低分辨率和高分辨率基准图具有相同稀疏系数的特点重建高分辨率地磁基准图。实验结果表明:所提方法对地磁基准图具有更高的构建精度，对训练所需的数据集有更低的需求，同时对噪声有更好的鲁棒性。与PSO-Kriging插值法相比，在4倍放大倍数下峰值信噪比(PSNR)由26.31 dB提高至26.73 dB，结构相似度(SSIM)由0.498提高至0.524，均方根误差(RMSE)由14.96 nT减小至13.78 nT。      

The features of radiation dose variations onboard ISS and Mir space station: comparative study.

The dynamics of the ISS-measured radiation dose variations since August 2000 is studied. Use is made of the data obtained with the R-16 instrument, which consists of two ionization chambers behind different shielding thicknesses. The doses recorded during solar energetic particle (SEP) events are compared with the data obtained also by R-16 on Mir space station. The SEP events in the solar maximum of the current cycle make a much smaller contribution to the radiation dose compared with the October 1989 event recorded on Mir space station. In the latter event, the proton intensity was peaking during a strong magnetic storm. The storm-time effect of solar proton geomagnetic cutoff decreases on dose variations is estimated. The dose variations on Mir space stations due to formation of a new radiation belt of high-energy protons and electrons during a sudden commencement of March 24, 1991 storm are also studied. It was for the first time throughout the ISS and Mir dose measurement period that the counting rates recorded by both R-16 channels on ISS in 2001-2002 were nearly the same during some time intervals. This effect may arise from the decreases of relativistic electron fluxes in the outer radiation belt.     

Design and performance of a vacuum-UV simulator for material testing under space conditions

This paper describes the construction and performance of a VUV-simulator that has been designed to study degradation of materials under space conditions. It is part of the Complex Irradiation Facility at DLR in Bremen, Germany, that has been built for testing of material under irradiation in the complete UV-range as well as under proton and electron irradiation. Presently available UV-sources used for material tests do not allow the irradiation with wavelengths smaller than about 115 nm where common Deuterium lamps show an intensity cut-off. The VUV-simulator generates radiation by excitation of a gas-flow with an electron beam. The intensity of the radiation can be varied by manipulating the gas-flow and/or the electron beam.     

Creation of model of quasi-trapped proton fluxes below Earth’s radiation belt

The object of investigation is the phenomenon of proton (from tens keV to several MeV) flux enhancement in near-equatorial region (L < 1.15) at altitude up to ∼1300 km (the storm-time equatorial belt). These fluxes are quite small but the problem of their origin is more interesting than the possible damage they can produce. The well known sources of these protons are radiation belt and ring current. The mechanism of transport is the charge-exchange on neutral hydrogen of exosphere and the charge-exchange on oxygen of upper atmosphere. Therefore this belt is something like the ring current projection to low altitudes. Using the large set of satellites data we obtain the average energy spectrum, the approximation of spectrum using kappa-function, the flux dependence on L, B geomagnetic parameters. On the basis of more than 30 years of experimental observations we made the empiric model that extends model of proton fluxes below 100 keV in the region of small L-values (L < 1.15). The model was realized as the package of programs integrated into COSRAD system available via Internet. The model can be used for revision of estimation of dose that low-orbital space devices obtain.     

MONITORING OF ENERGETIC PARTICLE ENVIRONMENT INSIDE THE CHINA-BRAZIL EARTH RESOURCE SATELLITE

On 14 October 1999, the Chinese-Brazil earth resource satellite (CBERS-1) was launched in China. On board of the satellite there was an instrument designed at Peking University to detect the energetic particle radiation inside the satellite so the radiation fluxes of energetic particles in the cabin can be monitored continuously. Inside a satellite cabin, radiation environment consists of ether penetrated energetic particles or secondary radiation from satellite materials due to the interactions with primary cosmic rays.Purpose of the detectors are twofold, to monitor the particle radiation in the cabin and also to study the space radiation environment The data can be used to study the radiation environment and their effects on the electronics inside the satelhte cabin. On the other hand, the data are useful in study of geo-space energetic particle events such as solar proton events, particle precipitation and variations of the radiation belt since there should be some correlation between the radiation situation inside and outside the satellite.The instrument consists of two semi-conductor detectors for protons and electrons respectively. Each detector has two channels of energy ranges. They are 0.5-2MeV and ≥2MeV for electrons and 5-30MeV and 30-60MeV for protons. Counting rate for all channels are up to 104/(cm2@s)and power consumption is about 2.5 W. There are also the additional functions of CMOS TID (total integrated dose) effect and direct SEU monitoring. The data of CBMC was first sent back on Oct. 17 1999 and it's almost three years from then on. The detector has been working normally and the quality of data is good.The preliminary results of data analysis of CBMC not only reveal the effects of polar particle precipitation and radiation belt on radiation environment inside a satellite, but also show some important features of the geo-space energetic particle radiation.As one of the most important parameters of space weather, the energetic charged particles have great influences on space activities and ground tech nology. CBMC is perhaps the first long-term on-board special equipment to monitor the energetic particle radiation environment inside the satellite and the data it accnmulated are very useful in both satellite designing and space research.     

Instantaneous BeiDou–GPS attitude determination: A performance analysis

The advent of modernized and new global navigation satellite systems (GNSS) has enhanced the availability of satellite based positioning, navigation, and timing (PNT) solutions. Specifically, it increases redundancy and yields operational back-up or independence in case of failure or unavailability of one system. Among existing GNSS, the Chinese BeiDou system (BDS) is being developed and will consist of geostationary (GEO) satellites, inclined geosynchronous orbit (IGSO) satellites, and medium-Earth-orbit (MEO) satellites. In this contribution, a BeiDou–GPS robustness analysis is carried out for instantaneous, unaided attitude determination.