Deorbiter CubeSat mission design

This paper presents the mission design for a CubeSat-based active debris removal approach intended for transferring sizable debris objects from low-Earth orbit to a deorbit altitude of 100 km. The mission consists of a mothership spacecraft that carries and deploys several debris-removing nanosatellites, called Deorbiter CubeSats. Each Deorbiter is designed based on the utilization of an eight-unit CubeSat form factor and commercially-available components with significant flight heritage. The mothership spacecraft delivers Deorbiter CubeSats to the vicinity of a predetermined target debris, through performing a long-range rendezvous maneuver. Through a formation flying maneuver, the mothership then performs in-situ measurements of debris shape and orbital state. Upon release from the mothership, each Deorbiter CubeSat proceeds to performing a rendezvous and attachment maneuver with a debris object. Once attached to the debris, the CubeSat performs a detumbling maneuver, by which the residual angular momentum of the CubeSat-debris system is dumped using Deorbiter’s onboard reaction wheels. After stabilizing the attitude motion of the combined Deorbiter-debris system, the CubeSat proceeds to performing a deorbiting maneuver, i.e., reducing system’s altitude so much so that the bodies disintegrate and burn up due to atmospheric drag, typically at around 100 km above the Earth surface. The attitude and orbital maneuvers that are planned for the mission are described, both for the mothership and Deorbiter CubeSat. The performance of each spacecraft during their operations is investigated, using the actual performance specifications of the onboard components. The viability of the proposed debris removal approach is discussed in light of the results.     

Estimating the spin axis orientation of the Echostar-2 box-wing geosynchronous satellite

For the first time, the spin axis orientation of an inactive box-wing geosynchronous satellite has been estimated from ground-based optical photometric observations of Echostar-2’s specular reflections. Recent photometric light curves obtained of Echostar-2 over four years suggest that unusually bright and brief specular reflections were occurring twice within an observed spin period. These bright and brief specular reflections suggested two satellite surfaces with surface normals separated by approximately 180°. The geometry between the satellite, the Sun, and the observing location at the time of each of the brightest observed reflections, was used to estimate Echostar-2’s equatorial spin axis orientation coordinates. When considering prograde and retrograde rotation, Echostar-2’s spin axis orientation was estimated to have been located within 30° of either equatorial coordinate pole. Echostar-2’s spin axis was observed to have moved approximately 180° in right ascension, within a time span of six months, suggesting a roughly one year spin axis precession period about the satellite’s angular momentum vector.     

河北省高校农村生源学生思想现状调查研究

河北省农村人口占总人口的79％，是一个比较典型的农业大省。农村生源大学生，是河北省在校大学生的重要组成部分，占生源的最大比例。大学生是宝贵的人才资源，他们的素质尤其是思想政治素质如何，他们能否成为社会主义事业的合格建设者和可靠接班人，是一个非常重要的问题。因而，科学分析和把握他们的思想政治状况，将会增强我们把握大学生思想脉搏的准确性和说服力。为此笔者选取了河北省八个地市的不同高校，进行了问卷调查、座谈和访谈。对河北省农村生源大学生的思想现状进行了调查。通过统计软件的录入和整理，统计结果比较真实地显示了当前河北省农村生源大学生的思想现状。     

态势评估领域知识的表示方法研究

从分析态势评估专家系统的结构出发,研究战场态势评估知识库的构建,进而对态势评估的领域知识进行归纳,并通过示例探讨对态势评估领域知识的表示方法,同时把可信度方法引入态势评估不确定性知识的表示,给出了复合条件可信度的计算方法。     

国外气象卫星发展及其趋势

综观27年气象卫星发展历程,展望未来13年前景,气象卫星的发展具有三多(多波段、多层次、多国别),三性(综合性、国际性、规范性)的特点,以保证所得资料具有连续性、可靠性和通用性。     

航天器安全防护保障探讨

把对航天器安全的威胁分为硬和软两大类，分析了对航天器产生威胁的类别，以及为保证航天器安全而需要采取的措施。介绍了研究的内容，需要建设的空间信息对抗系统和空间信息探测网。     

基于中介理论与交通特性的终端区态势评价

终端区交通态势的准确度量是制定并实施流量管理措施的重要依据之一。通过提取终端区宏观与微观的交通特性,从进离场及总量3个维度构建态势的指标描述,并进一步采用中介理论中的真值程度度量与熵权法建立了一种客观的终端区飞行区交通态势模糊综合评价方法,实现客观、准确的交通态势判别与样本间量化比较。选取国内典型繁忙终端区的实测数据,验证了评价方法与特性指标的有效性。     

Flight safety measurements of UAVs in congested airspace

Describing spatial safety status is crucial for high-density air traffic involving multiple unmanned aerial vehicles (UAVs) in a complex environment. A probabilistic approach is proposed to measure safety situation in congested airspace. The occupancy distribution of the airspace is represented with conflict probability between spatial positions and UAV. The concept of a safety envelope related to flight performance and response time is presented first instead of the conventional fixed-size protected zones around aircraft. Consequently, the conflict probability is performance-dependent, and effects of various UAVs on safety can be distinguished. The uncer-tainty of a UAV future position is explicitly accounted for as Brownian motion. An analytic approximate algorithm for the conflict probability is developed to decrease the computational consumption. The relationship between safety and flight performance are discussed for different response times and prediction intervals. To illustrate the applications of the approach, an experi-ment of three UAVs in formation flight is performed. In addition, an example of trajectory planning is simulated for one UAV flying over airspace where five UAVs exist. The validation of the approach shows its potential in guaranteeing flight safety in highly dynamic environment.     

大城市消费者对日本大米的购买意愿及其影响因素——以北京市为例

对北京市的消费者对日本大米的认知程度、接受程度和购买意愿及其影响因素等问题进行了问卷调查.通过对所得数据进行分析,得出女性消费者、购买食品时对价格较为关注的消费者更倾向于购买日本大米;消费者的学历、收入、家庭人口数、受教育程度、时间压力、对食品质量安全的关心程度、对日本大米的了解程度与是否购买日本大米、购买日本大米量的多少呈正相关关系;而消费者年龄、价格在影响消费者购买日本大米的行为上并不显著.最后,依据上述结论,给出相关的政策建议.     

飞机燃油密度实时测量及其实现方法

主要讨论了飞机燃油量实时测量的有关问题，并就其中燃油密度测量这一关键环节进行了重点论述，对密度测量的重要性、测量方法和国内外的研究状况进行了探讨。