Statistical validation of HZETRN as a function of vertical cutoff rigidity using ISS measurements

Measurements taken in Low Earth Orbit (LEO) onboard the International Space Station (ISS) and transit vehicles have been extensively used to validate radiation transport models. Primarily, such comparisons were done by integrating measured data over mission or trajectory segments so that individual comparisons to model results could be made. This approach has yielded considerable information but is limited in its ability to rigorously quantify and differentiate specific model errors or uncertainties. Further, as exploration moves beyond LEO and measured data become sparse, the uncertainty estimates derived from these validation cases will no longer be applicable. Recent improvements in the underlying numerical methods used in HZETRN have resulted in significant decreases in code run time. Therefore, the large number of comparisons required to express error as a function of a physical quantity, like cutoff rigidity, are now possible. Validation can be looked at in detail over any portion of a flight trajectory (e.g. minute by minute) such that a statistically significant number of comparisons can be made. This more rigorous approach to code validation will allow the errors caused by uncertainties in the geometry models, environmental models, and nuclear physics models to be differentiated and quantified. It will also give much better guidance for future model development. More importantly, it will allow a quantitative means of extrapolating uncertainties in LEO to free space. In this work, measured data taken onboard the ISS during solar maximum are compared to results obtained with the particle transport code HZETRN. Comparisons are made at a large number (∼77,000) of discrete time intervals, allowing error estimates to be given as a function of cutoff rigidity. It is shown that HZETRN systematically underestimates exposure quantities at high cutoff rigidity. The errors are likely associated with increased angular variation in the geomagnetic field near the equator, the lack of pion production in HZETRN, and errors in high energy nuclear physics models, and will be the focus of future work.     

超宽带电磁脉冲天线阵互耦效应研究

将超宽带电磁脉冲天线组阵后可提高主射方向的峰值功率及增益。但由于非线性阵元因素,必须考虑阵元间互耦效应。以恒阻抗TEM喇叭天线为阵元,通过仿真和实验研究了超宽带天线阵的互耦效应,研究表明,耦合强弱与阵元间距及频段有关,互耦增强了超宽带天线阵的低频辐射能力,使远场主射方向脉冲峰峰值有所增加。上述结论对于超宽带电磁脉冲天线阵的应用具有参考价值。     

Spectral analysis of time-integrated Konus–Wind GRBs: Implication on radiative mechanisms

We have analysed a sample of 328 time-integrated GRB prompt emission spectra taken via the Konus instrument on board the US GGS-Wind spacecraft between 2002 and 2004 using a couple of two-components models, Cut-off Power Law (CPL) + Power Law (PL) and blackbody (BB) + PL. The spectra show clear deviation from the Band function. The PL term is interpreted as the low energy tail of a nonthermal emission mechanism. The distributions of corresponding index β give values β < −2/3 consistent with synchrotron and synchrotron self-Compton mechanisms. The distribution of low energy index α associated with the CPL term shows clear discordance with synchrotron models for 31.4% of the analysed GRBs with values exceeding that for the line of death, α = −2/3. Then, a set of nonthermal radiation mechanisms producing harder slopes, i.e., α > −2/3, are presented and discussed. For the remaining majority (68.6%) of GRBs with CPL index α < −2/3, we show that optically thin synchrotron produced by a power law electron distribution of type, N(γ) ∼ γ^−p, γ₁ < γ < γ₂, for finite energy range (γ₂ ≠ ∞) is a likely emission mechanism with α ∼−(p + 1)/2 in the frequency range ν₁ ? ν ? ν₂ (where ν₂ = η²ν₁ with η = γ₂/γ₁), such that for p > 1/3, one gets α < −2/3. We also show that corresponding spectra in terms of F_ν and νF_ν functions are peaked around frequency ν₂ instead of ν₁, respectively for p < 1 and p < 3. Besides, thermal emission is examined taking a single Planck function for fitting the low energy range. It can be interpreted as an early emission from the GRB fireball photosphere with observed mean temperature, kT′ ∼ 16.8 keV. Furthermore, we have performed a statistical comparison between the CPL + PL and BB + PL models finding comparable χ²-values for an important fraction of GRBs, which makes it difficult to distinguish which model and specific radiation mechanism (possible thermal or nonthermal γ-ray emissions) are best suitable for describing the reported data. Therefore, additional information for those bursts, such as γ-ray polarization, would be highly desirable in future determinations of GRBs observational data.     

Solar sail near the Sun: Point-like and extended models of radiation source

Some modifications of solar sail radiation pressure forces on a plate and on a sphere for use in the numerical simulation of ‘local-optimal’ (or ‘instantaneously optimal’) trajectories of a spacecraft with a solar sail are suggested. The force model development is chronologically reviewed, including its connection with solar sail surface reflective and thermal properties. The sail surface is considered as partly absorbing, partly reflective (specular and diffuse), partly transparent. Thermal balance is specified because the spacecraft moves from circular Earth orbit to near-Sun regions and thermal limitations on the sail film are taken into account. A spherical sail-balloon can be used in near-Sun regions for scientific research beginning with the solar-synchronous orbit and moving outward from the Sun. The Sun is considered not only as a point-like source of radiation but also as an extended source of radiation which is assumed to be consequently as a point-like source of radiation, a uniformly bright flat solar disc and uniformly bright solar sphere.     

空间光学遥感器天然辐射效应数据库研究

空间环境是诱发卫星异常和故障的主要原因之一。光学遥感器作为卫星最重要的有效载荷之一，在空间会受到空间辐射环境的影响。因此在研制光学遥感器的同时，需要同时考虑空间辐射环境因素，文章就空间光学遥感器天然辐射效应数据库的设计和应用进行了介绍。     

星载反射阵天线形变对其辐射特性的影响

高增益、低剖面、低质量的平面反射阵天线广泛应用于卫星通信及空间探测领域.目前虽有多种新型星载反射阵天线设计,但尚未大规模实际应用.反射阵天线在加工、组装过程中出现的误差以及在空间高低温环境中产生的形变误差都会对其电特性产生影响.为验证反射阵天线大规模实际应用于空间探测的可行性,研究了反射阵天线可能出现的形变误差对其辐射特性的影响,从理论上分析了反射阵单元发生位移、旋转、变形时反射相位的变化规律,并且从反射阵天线设计实例出发,利用科学计算和电磁仿真软件对天线的方向图、增益等特性进行仿真分析,研究形变对反射阵天线电性能的影响.     

基于混响室的电磁环境及自然环境综合试验箱设计和仿真技术

本文提出一种基于混响室平台将电磁环境和自然环境结合的综合试验箱集成技术,该试验箱集成了环境试验条件和电磁辐射敏感度试验条件,可以在高低温、湿热、温度循环、温度冲击等多种环境条件下同时对电子设备施加电磁辐射干扰,考核电子设备在同施加环境应力和电磁应力的复杂条件下的适应性。经过设计、建造和测试,该集成技术满足各项预期指标并容易进行推广,可进一步降低设备试验成本。     

北斗MEO卫星辐射剂量探测数据缺失值处理方法

针对北斗MEO卫星辐射剂量探测数据出现连续性缺失的问题,开展缺失值处理方法研究.提出一种叠加正弦波的线性样条回归方法,即引入样条函数,对各数据连续缺失的时间段进行分段处理,每段样条采用叠加正弦波的线性方程填充缺失值.结果表明：利用该方法处理缺失值,每段样条中填充曲线与探测曲线在增长趋势、周期性波动等方面具有较高的一致性;相比前向插值法和线性插值法,其填充值与真实值误差更小,关联性更高.该方法较好地解决了数据连续缺失的问题,形成了完整性好、准确性高的北斗MEO卫星辐射剂量数据集,为后续数据的发布、建模和可视化展示等奠定了基础.     

临近空间太阳紫外辐射环境模拟与地区差异

太阳紫外辐射是临近空间能量输入的主要来源之一,对其在中层大气的辐射特性进行研究,是研究临近空间大气成分与密度变化、光化学反应以及动力学过程的重要基础。依托“鸿鹄”临近空间探测专项计划,利用MODTRAN5辐射传输模型及卫星实测数据,模拟并对比中国11个主要地形区上空临近空间（20~50 km）紫外辐射（200~400 nm）垂直分布和季节演变的异同,计算了臭氧含量、太阳天顶角和日地距离等关键因素对辐射强度的影响。结果表明,各地形区的辐射流量垂直分布廓线和年较差垂直分布廓线较为一致,在地理位置上毗邻的地区辐射特性及季节演变较为接近,但在太阳紫外的不同波段之间区别较大。研究成果为临近空间探测实验提供了数据支撑,为大气反演等相关领域提供参考。     

“风云一号”(B)星对内辐射带质子的观测结果

本文介绍“风云一号”(B)星上的“宇宙线成份监测器”于1990年11月19至24日对内辐射带质子的观测结果。通过对这些结果的分析, 本文获得了4—23MeV能量范围内辐射带质子垂直强度在磁坐标内的分布特征。同时, 本文还给出了100°E子午面内质子垂直强度的分布。分析表明, 所得结果与辐射带理论一致。