Simulation of ASTROD I test mass charging due to solar energetic particles and interplanetary electrons

As ASTROD I travels through space, its test mass will accrue charge due to exposure of the spacecraft to high-energy particles. This test mass charge will result in Coulomb forces between the test mass and the surrounding electrodes. In earlier work, we have used the GEANT 4 toolkit to simulate charging of the ASTROD test mass due to cosmic-ray protons of energies between 0.1 and 1000 GeV at solar maximum and at solar minimum. Here we use GEANT 4 to simulate the charging process due to solar energetic particle events and interplanetary electrons. We then estimate the test mass acceleration noise due to these fluxes. The predicted charging rates range from 2247 e⁺/s to 47,055 e⁺/s, at peak intensity, for the four largest SEP events in September and October 1989. Although the noise due to charging exceeds the ASTROD I budget for the two larger events, it can be suppressed through continuous discharging. The acceleration noise during the two small events is well below the design target. The charging rate of the ASTROD I test mass due to interplanetary electrons in this simulation is about −11% of the cosmic-ray protons at solar minimum, and over −37% at solar maximum. In addition to the Monte Carlo uncertainty, an error of ±30% in the net charging rates should be added to account for uncertainties in the spectra, physics models and geometry implementations.     

Evidence for a Two-Stage Acceleration Process in Large Solar Energetic Particle Events

Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we surveyed the event-averaged ∼0.1–60 MeV/nuc heavy ion elemental composition in 64 large solar energetic particle (LSEP) events of cycle 23. Our results show the following: (1) The Fe/O ratio decreases with increasing energy up to ∼10 MeV/nuc in ∼92% of the events and up to ∼60 MeV/nuc in ∼64% of the events. (2) The rare isotope ³He is greatly enhanced over the corona or the solar wind values in 46% of the events. (3) The heavy ion abundances are not systematically organized by the ion’s M/Q ratio when compared with the solar wind values. (4) Heavy ion abundances from C–Fe exhibit systematic M/Q-dependent enhancements that are remarkably similar to those seen in ³He-rich SEP events and CME-driven interplanetary (IP) shock events. Taken together, these results confirm the role of shocks in energizing particles up to ∼60 MeV/nuc in the majority of large SEP events of cycle 23, but also show that the seed population is not dominated by ions originating from the ambient corona or the thermal solar wind, as previously believed. Rather, it appears that the source material for CME-associated large SEP events originates predominantly from a suprathermal population with a heavy ion enrichment pattern that is organized according to the ion’s mass-per-charge ratio. These new results indicate that current LSEP models must include the routine production of this dynamic suprathermal seed population as a critical pre-cursor to the CME shock acceleration process.     

低轨航天器运行环境质子通量预测模型对比研究

辐射带粒子环境是导致航天器故障和异常的重要因素。为此,需要对辐射带粒子环境及其通量分布进行研究。文章主要研究低地球轨道（LEO）环境辐射带质子分布情况。分析了目前用来计算质子通量的几种常用模型的优缺点;利用各模型计算了不同轨道的质子通量,对计算结果进行了比较;总结了进行不同高度、不同能量范围的质子通量计算时,选择不同模型的依据原则。     

固态颗粒空间环境下升华过程数值分析

在轨液体的排放将产生毫米级固态颗粒空间碎片,由于其升华耗散过程具有不确定性,若长期留轨将产生危害。文章以水为例,通过数值模拟对冰粒在轨升华过程进行分析。结果表明,冰粒的太阳吸收比是影响其升华的重要因素,采取措施提高颗粒的太阳吸收比和减少单个颗粒的平均质量都可有效加快颗粒的升华耗散。     

2DEM—二维欧拉多流体计算方法

本文计算采用欧拉坐标系,在物质界面两侧布不同的标志点来描述界面的位置。每一个时间步长分解为拉氏计算、物质输运及扩散三步来完成。文中给出对平板凹槽问题及冲出波绕角问题的计算结果。     

Particle Acceleration by the Sun: Electrons, Hard X-rays/Gamma-rays

Observations of hard X-ray (HXR)/γ-ray continuum and γ-ray lines produced by energetic electrons and ions, respectively, colliding with the solar atmosphere, have shown that large solar flares can accelerate ions up to many GeV and electrons up to hundreds of MeV. Solar energetic particles (SEPs) are observed by spacecraft near 1 AU and by ground-based instrumentation to extend up to similar energies, but it appears that a different acceleration process, one associated with fast Coronal Mass Ejections (CMEs) is responsible. Much weaker SEP events are observed that are generally rich in electrons, ³He, and heavy elements. The energetic particles in these events appear to be similar to those accelerated in flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission provides high-resolution spectroscopy and imaging of flare HXRs and γ-rays. The observations of the location, energy spectra, and composition of the flare accelerated energetic particles at the Sun strongly imply that the acceleration is closely related to the magnetic reconnection that releases the energy in solar flares. Here preliminary comparisons of the RHESSI observations with observations of both energetic electrons and ions near 1 AU are reviewed, and the implications for the particle acceleration and escape processes are discussed.     

Relative ion Fe,C and O abundances in quiet time particle fluxes in the 23 SC

Using ACE and SOHO data the origin of quiet-time low-energy particle fluxes at 1 AU is studied in the 23rd solar cycle. One of the selection criteria of quiet-time periods is to demand that H/He < 10 provided that periods with noticeable contribution of remnants of gradual events have been excluded from consideration. Our results suggest different origin of 0.03–3 MeV/nucleon particles – different seed populations accelerated and different acceleration processes. During the ascending, maximum and descending phases of solar activity quiet-time ions consist of coronal particles accelerated to suprathermal energies in about a half of the quiet periods, the rest of quiet-time fluxes originates from particle acceleration in processes similar to those in small impulsive solar flares rich in Fe. At solar minimum the bulk solar wind particles serve as seed population.     

Neuroimmune response and sleep studies after whole body irradiation with high-LET particles

In order to investigate the biological effects of galactic rays on astronaut cerebral functions after space flight, mice were exposed to different heavy ions (HZE) in whole-body conditions at doses comparable to the galactic flux: ¹²C, ¹⁶O and ²⁰Ne (95 MeV/u, at 42–76 mGy). Animals were also exposed to 42 mGy of ⁶⁰Co radiation for comparison with HZE. The neuroimmune response, evaluated by interleukin-1 (IL-1) measurement, showed that this cytokine was produced 3 h after irradiation by ¹⁶O or ⁶⁰Co. In contrast, neither ¹²C (56.7 mGy) nor ²⁰Ne (76 mGy) induced IL-1 production. However, immunohistochemical staining of ¹²C-irradiated mouse brain tissue showed 2 months later a marked inflammatory reaction in the hippocampus and a diffuse response in parenchyma. Sleep studies were realized before and after exposure to 42 mGy of ¹⁶O and 76 mGy of ²⁰Ne: only the ²⁰Ne radiation displayed a small effect. A slight decrease in paradoxical sleep, corresponding to a reduction in the number of episodes of paradoxical sleep, was manifested between 8 and 22 days after exposure. Exposure to ¹²C and ¹⁶O induced no changes either in cellularity of spleen or thymus, or in caspase 3 activity (as much as four months after irradiation). Taken together, these data indicate that the CNS could be sensitive to heavy ions and that responses to HZE impact depend on the nature of the particle, the dose threshold and the time delay to develop biological processes. Differences in responses to different HZE highlight the complex biological phenomena to which astronauts are submitted during space flight.     

多相流环境下绝热材料烧蚀试验方法研究

为深入了解高温多相流环境中绝热材料烧蚀规律，以氧-煤油烧蚀试验系统为基础，采用氧化硼(B2O3)粉末为添加粒子，发展了一种用于绝热材料烧蚀性能测试的新方法，并进行了验证测试。结果表明：氧-煤油烧蚀试验系统的温度为500~2700 K，射流速度为200~1500 m/s，可通过调整燃烧室压力、烧蚀距离和粒子浓度等参数适应各种烧蚀工况；B2O3颗粒在高温射流中发生熔化、蒸发等相变，可用于模拟火箭发动机中的凝聚相粒子；验证试验中绝热材料的烧蚀率和烧蚀规律与其他多相流烧蚀试验结果相近。结果证明该装置可用于开展多相流环境下绝热材料烧蚀试验研究。     

SAA drift: Experimental results

According to the paleomagnetic analysis there are variations of Earth’s magnetic field connected with magnetic moment changing. These variations affect on the South Atlantic Anomaly (SAA) location. Indeed different observations approved the existence of the SAA westward drift rate (0.1–1.0 deg/year) and northward drift rate (approximately 0.1 deg/year).