“哈勃”的太空维修传奇

正2018年10月5日,由于哈勃空间望远镜的陀螺仪出现问题,美国宇航局(NASA)地面控制中心“哈勃”小组,宣布哈勃空间望远镜进入安全模式,暂停太空探测任务。到2018年年底,哈勃空间望远镜(以下简称“哈勃”)已经服役了整整28年,超过设计寿命13年。这可以看做是工程史上的奇迹。虽然航天飞机退役后,在轨维修“哈勃”已经是不可能的任务了,但在这20多年时间里,“哈     

“哈勃”空间望远镜将面临三种选择

“哈勃”空间望远镜将面临三种选择□□从2003年初开始,普林斯顿高等研究院的一个专家小组受美国航宇局委托,就如何让“哈勃”空间望远镜更妥善地“寿终正寝”展开调研,并于最近向美国政府呈交了报告。报告认为,美国“哈勃”空间望远镜未来可以有三种选择,其中最理想的一种是在2010年前发射两架航天飞机对其进行维修,以延长这台望远镜的寿命,最大限度利用它的科学观测能力。报告中提出的另外两种方案:一种是在2006年底前派一架航天飞机对“哈勃”空间望远镜进行维修,另一种是不发射航天飞机,在“哈勃”望远镜科学价值用尽后利用无人航天器控…     

航天简讯

哈勃空间望远镜因主镜缺陷大大影响了空间观测,科学家们强烈要求美航宇局(NASA)尽快给予维修或更换部件。现正准备用喷气推进研究所(JPL)的“广角行星摄象机(WF/PC)在轨进行交换,以便进行光学系统的修正。而对欧空局搭载在哈勃空间望远镜上的“欧洲微光天体摄象机”未打算更换,它是哈勃空间望远镜上所有探测器中析象度最高的一个,因主镜缺陷的影响使其析象本领大为降低,因此,科学家们也要求对它进行修理。     

“哈勃”维修十大要点

正哈勃空间望远镜(以下简称“哈勃”)和此前的空间望远镜有一个很大的区别,它从设计之初就考虑了周期性地接受维护。当时考虑,是依托航天飞机,每两年半到三年接受一次维护和设备升级,不断地改进观测能力。这样,“哈勃”就可以不断引入最前沿的科技成果。这种维护和升级任务称为“服务任务”,简称SM。“哈勃”的维修和维护,不但为天文界维持了一件重要的科学仪器,同样也为后续的在轨维修和维护总结出了一套行之有效的工作组     

在轨地球同步卫星自主工程测控研究

地球同步卫星在轨工程测控任务通常由地面测控系统完成. 随着技术水平的发展, 如果在轨地球同步卫星能够实现自主工程测控, 将大大减轻地面测控系统负担, 提高卫星独自生存能力, 降低系统运行成本, 并将成为卫星测控技术新的发展方向. 本文提出卫星自主在轨测控方案, 研究了当前地球同步卫星在轨工程测控的主要项目及实现算法. 对其进行的可行性分析表明, 尽管受到轨道测量能力的制约, 在轨地球同步卫星仍可实现完全或地面有限参与情况下的自主工程测控. 在此基础上, 设计了一种地球同步在轨卫星完全自主工程测控的原理方案, 通过分析其技术难点及存在的风险, 提出应对措施. 研究结果表明, 基于目前卫星制造水平和成熟的在轨测控技术, 实现在轨地球同步卫星自主工程测控技术可行, 其是解决卫星数量急剧增加与地面测控能力有限这一突出矛盾的有效途径.      

基于在轨组装维护的模块化深空探测器技术进展与应用研究

在轨组装与维护是航天器在轨服务技术的基本内容,而模块化设计则是实现航天器在轨组装与维护的一项主要支撑技术。调研总结了国外深空探测领域模块化航天器设计以及在轨组装与在轨维护实施的技术进展,主要包括模块化地外行星着陆探测器、大型在轨组装深空探测器、布置于SEL2(Sun-Earth Libration 2)等轨道的超大型在轨组装空间望远镜系统等,分析了深空探测器领域应用模块化设计实现在轨组装与维护的关键技术要素。针对深空探测航天器长寿命、高可靠、特殊推进系统及其设备配套等技术特点与需求,提出一种应用在轨组装与维护技术的火星多任务探测器系统设想,介绍了探测器系统的任务架构、基本组成、轨道策略等,为我国深空探测技术发展以及新型深空探测器研制提供参考。     

在轨3D打印及装配技术在深空探测领域的应用研究进展

以太阳帆深空探测为引子,对以在轨3D打印及装配技术为基础的在轨制造技术的必要性和可行性进行分析,分别阐述了在轨3D打印技术的技术优势、技术可行性以及在轨装配的最新研究进展,并重点研究了美国NASA资助的“蜘蛛制造”在轨制造技术,此项研究成功地将在轨3D打印和空间自主装配有机结合起来,有望突破目前空间可展开机构无法达到万米量级的技术局限性,为中国深空探测的发展提供了一种可供选择的发展思路。     

宇航员妙手回春 哈勃望远镜复明

1999年12月19日美国东部时间晚上7点50分,发现号航天飞机从肯尼迪航天中心起飞。发现号这次飞行的主要任务是为“患病”的哈勃空间望远镜实施手术。 “千里眼”积劳成疾 哈勃空间望远镜以著名天文学家、星系天文学的奠基人哈勃的名字命名,是迄今为止在轨运行的最大的天文望远镜,价值30亿美元,可以观测到140亿光年远的天体,被称为“太空千里眼”。1990年4月24日,它由     

未来的天文卫星

1989年,美国研制的,价值12亿美元的哈勃空间望远镜将进入太空,开始它历时15年的探测使命。哈勃望远镜能使用可见光、近紫外线/红外线(1200～11000埃)进行观测,能为理论宇宙学家、行星际专家等所有的天文学家提供极为丰富的数据。哈勃望远镜的发射将标志天文卫星发展到一个崭新阶段。今后10年,人们将发射各种类型的自由飞行天文卫星,采用各种观测技术,探测宇宙中大量的γ射线,x射线、紫外线、红外线、微波以及无线电波,因此天文科学将会有新的发展。     

"哈勃"的新图像太空中的蝌蚪和老鼠

今年3月份,美国航宇局派出7名航天员乘坐哥伦比亚号航天飞机升到太空,对哈勃空间望远镜进行了第四次大的维修。维修项目中包括为它安装了一架价值7600万美元的先进测绘照相机,换下了原来的暗天体照相机。4月初,“哈勃”恢复     

Research on the Relation Between the Seeker's Handover and the Geometrical Position of the Missile and the Target

 研究了雷达导引头的交班误差以及截获概率与交班时刻弹目几何位置的关系,提出了单个误差角的导引头天线指向角误差模型,它与两个误差角的导引头指向角误差模型相比可以更好地分析天线指向角误差,并得到使指向角误差最小的弹目几何位置;然后进一步得到使多普勒频率误差最小的弹目几何位置;给出了最终的截获概率的表达式,截获概率由目标处于导引头天线主波束的概率、目标回波多普勒频率落入接收机频带内的概率和目标的检测概率组成的;最后分析了一种典型的中末交班情况.     

火星地形对火星大气运动的影响及火星尘暴发生的可能机制

本文在准地转模式的假定下,讨论了火星地形对火星大气的影响,并根据文章所提供的信息对火星尘暴发生的物理机制作了粗略的解释。      

Comparison of the magnetic field before the subsolar magnetopause with the magnetic field in the solar wind before the bow shock

Crossings of the magnetopause near the subsolar point are analyzed using data of THEMIS mission. Variations of the magnetic field near magnetopause measured by one of THEMIS satellites are studied and compared with simultaneous measurements in the solar wind by another THEMIS satellite. The time delay of the solar wind arrival at the subsolar point of the magnetopause is taken into account. 30 and 90 s averaging of the magnetic field in the magnetosheath is produced. The results of averaging are compared with the results of measurements in the solar wind before the bow shock and foreshock. It is shown, that _Bx$B_x$ component of the magnetic field near magnetopause is near to zero, which supports the possibility to consider the magnetopause as the tangential discontinuity. Comparatively good correlation of _By$B_y$ component in the solar wind and near the magnetopause is observed. The correlation of _Bz$B_z$ component near the magnetopause and IMF is practically absent, the sign of the _Bz$B_z$ near the subsolar point does not coincide with the sign of IMF _Bz$B_z$ in ∼$\sim$30% cases.     

陀螺仪短周期性能测试方法研究

讨论了陀螺仪短周期重复性能的标定测试方法,即极轴翻滚试验方法。该方法以地球极轴为基准,通过对一周过程的电流值进行离散傅立叶分析,经过相应的运算处理求出误差模型参数的估计值。试验结果表明,该方法辨识参数多,全面反映了陀螺仪性能,可以科学地考察陀螺仪的短周期重复性。     

地磁暴恢复相中间层低热层高纬温度响应

利用TIMEGCM模拟了2005年9月10日至20日由日冕物质抛射引起的地磁暴事件,研究了此地磁暴恢复相高纬度中间层低热层（MLT）区域温度的变化,揭示了磁暴恢复相时温度、垂直风、总加热项和NO辐射冷却的内在联系.结果表明:地磁暴恢复相刚开始时,温度对磁暴的响应在晨侧为负扰动（降温）,在其他地区都为正扰动（增温）;随着磁暴的恢复,整个北半球都变为正的温度扰动（增温）.这种高纬MLT区域的温度响应主要与垂直风密切相关.当垂直风为正时,总加热为负,增温减弱;当垂直风为负时,总加热为正,增温变强.辐射冷却特别是NO辐射冷却作用在热层被称为恒温器,降低了磁暴期间80%的热层增温.但是,在MLT区域NO辐射冷却作用不明显,一般比总加热项小一个量级,对温度响应造成的影响较小.      

Method for the prediction of the effective dose equivalent to the crew of the International Space Station

This paper describes a methodology for assessing the pre-mission exposure of space crew aboard the International Space Station (ISS) in terms of an effective dose equivalent. In this approach, the PHITS Monte Carlo code was used to assess the particle transport of galactic cosmic radiation (GCR) and trapped radiation for solar maximum and minimum conditions through an aluminum shield thickness. From these predicted spectra, and using fluence-to-dose conversion factors, a scaling ratio of the effective dose equivalent rate to the ICRU ambient dose equivalent rate at a 10 mm depth was determined. Only contributions from secondary neutrons, protons, and alpha particles were considered in this analysis.     

Consequences of the application of the streamer fluid model to the study of the sprite inception mechanism

We present the results of a streamer-fluid model used to investigate the electrodynamical coupling between the troposphere and upper atmosphere due to the penetration of lightning electric fields into the mesosphere and the lower ionosphere, generating sprites. The model solves the continuity equation for electrons and ions coupled to Poisson equation. The dominant physical response of the atmosphere is the formation of a screening-ionization wave. The wave shields the atmosphere above it from the action of the lightning field and, together with the conductivity reduction below it due to attachment, the wave amplifies the total field below it, allowing for the penetration of intense electric fields in the mesosphere as it propagates downwards into regions of higher density that compress the wave. This is the key physical mechanism for sprite inception. We evaluated the effects of the thundercloud charge geometry, lightning current waveshape, atmospheric conductivity, via different electron density profiles, and the effect of ionization, attachment and electron mobility coefficients in the electrical breakdown process, related to halo production, and sprite streamer initiation. The results showed that electrons with higher mobility are more efficient in shielding the lightning electric field before breakdown, causing delay, and they contribute to the formation of the streamer seed after breakdown, anticipating the sprite streamer inception. Similarly, a higher effective ionization rate, produced by modifications in the attachment and ionization coefficients, anticipates sprite inception. The simulations with 6 different electron density profiles, and therefore conductivities, spanning 4 orders of magnitude, showed that the altitude of breakdown and sprite initiation, as well as their time delays from the lightning discharge are directly related to atmospheric conductivity: higher conductivities produce halo and sprite inception at lower altitudes with longer delays and may hinder sprite formation. We document that variations of 30 times in the lightning current leads to sprite initiation altitudes in the range 66.0–73.5 km, with delays between 1.550 and 34.500 ms, while variations of 4 orders of magnitude in the conductivity profile lead to initiation altitudes 61.0–70.6 km, with delays in the range 3.825–9.825 ms. Consequently, we suggest that lightning characteristics dominate over atmospheric parameters in determining sprites’ initiation altitude and delay. The simulation of a −CG, with a constant current of 30 kA, did not produce a sprite seed, confirming an asymmetry in the response of the atmosphere to positive and negative lightning. This is due to the free electron drift direction that is away from the screening ionization wave, preventing the formation of the streamer seed for the great majority of −CGs. The same does not apply to halos, which depend on the occurrence of breakdown and can be produced by discharges of both polarities.     

Influence of the Ionosphere on the Observation of the Mid-Latitude Pi2 Pulsations at the Global Scale

Results of our investigation showed that occurrence frequency of Pi2 over a 24 hour period undergoes seasonal variations in time coincidence with foF2. In the winter months, at sunrise and sunset (when foF2gradients are the largest) the observation probability of these oscillations is minimal. At periods of summer solstice when the F2-layer persists almost round the clock, no effect of Pi2 pulsation attenuation is observed at sunrise and sunset. The pulsation amplitudes behave in a similar manner. Results of this study suggest the conclusion that the propagation of signal from the Pi2 sourse into the mid-latitudes, and also the parameters of these pulsations are essentially affected by electron density in the ionospheric F2-layer.      

On the correlation of the solar wind observed at the L5 point and at the Earth

The L5 point is a promising location for forecasting co-rotating high-speed streams in the solar wind arriving at the Earth. We correlated the solar wind data obtained by the Nozomi spacecraft in interplanetary space and by the Advanced Composition Explorer (ACE) at the L1 point, and found that the correlation is significantly improved from that of the 27-day recurrence of ACE data. Based on the correlation between the two spacecraft observations, we estimated the correlation of the solar wind velocity between the L5 point and at the Earth, and found that the correlation coefficient was about 0.78 in late 1999, while that of the 27-day recurrence was 0.51. Eighty-eight percent of the velocity difference falls within 100 km/s between the L5 point and the Earth. This demonstrates the potential capability of solar wind monitoring at the L5 point to forecast the geomagnetic disturbances 4.5 days in advance.     

辐射变色薄膜剂量计性能测试及加速器应用

本课题的目的是建立用于辐射加工高剂量水平吸收剂量测量的辐射变色薄膜剂量计。通过系统研究,批量制备了以尼龙为基材,副品红氰化物为染料的辐射变色薄膜剂量计。为了验证批制辐射变色薄膜剂量测量的可靠性,选择了国际上应用较广的FWT-60膜及丙氨酸薄膜剂量计与本实验室批制的辐射变色薄膜开展实验室内剂量比对,比对结果均在±4%内符合,归一化偏差En绝对值均小于1。通过在加速器上进一步应用实验表明批制辐射变色薄膜可用于电子束辐照参数测量。