Optimal satellite formation reconfiguration actuated by inter-satellite electromagnetic forces

The inter-satellite electromagnetic forces generated by the magnetic dipoles on neighboring satellites provide an attractive control actuation alternative for satellite formation flight due to the prominent advantages of no propellant consumption or plume contamination. However, the internal force nature as well as the inherent high nonlinearity and coupling of electromagnetic forces bring unique dynamic characteristics and challenges. This paper investigates the nonlinear translational dynamics, trajectory planning and control of formation reconfiguration actuated by inter-satellite electromagnetic forces. The nonlinear translational dynamic model is derived by utilizing analytical mechanics theory; and analysis on the dynamic characteristics is put forward. Optimal reconfiguration trajectories of electromagnetic force actuated formation are studied by applying optimal control theory and the Gauss pseudospectral method. Considering the high nonlinearity and uncertainty in the dynamic model, an inner-and-outer loop combined control strategy based on feedback linearization theory and adaptive terminal sliding mode control is proposed with finite-time convergence capability and good robust performance. Theoretical analysis and numerical simulation results are presented to validate the feasibility of the proposed translational model, reconfiguration trajectory optimization approach and control strategy.     

Blue and red supergiants and the age structure of the NGC 330 region

We analysed new UBVRI CCD photometry of the massive, blue SMC cluster NGC 330 and its surrounding field. The age structure and a new reddening value for the stellar population in this region of the SMC are derived and the implications for star formation in this part of the SMC and for stellar evolution are discussed.Based on observations obtained at ESO, La Silla     

The entropy in groups – a clue to galaxy formation

The entropy in the hot X-ray gas in groups of galaxies is a fossil of the process of galaxy formation The amount of entropy in these low mass systems considerably exceeds that predicted from structure formation models. To explain these results requires “extra” energy which is a relic of the process of star formation and active galaxy heating. We present new XMM results on the entropy and entropy profiles. These results are inconsistent with pre-heating scenarios which have been developed to explain the entropy floor in groups but are broadly consistent with models of structure formation which include the effects of heating and/or the cooling of the gas. The total entropy in these systems provides a strong constraint on all models of galaxy and group formation, and on the poorly defined feedback process which controls the transformation of gas into stars and thus the formation of structure in the universe.     

VPTIG焊接机器人在铝合金贮箱箱底生产中的应用

简要介绍了焊接机器人系统结构特征,采用VPTIG单面焊双面成型技术进行2A14铝合金焊接试验,获得良好的焊接接头性能,总结出可靠的工艺控制方法.并应用于铝合金贮箱箱底的生产中,产品焊缝经过RT探伤、液压气密试验、氦质谱检漏等检测方法,各项技术指标满足设计要求.     

简化导航算法在导弹飞行试验安全分析中的应用

安全分析是反舰导弹飞行试验前必须开展的一项重要工作,安全分析以导弹弹道数据为基础,而弹道仿真模型获取不易。基于此,提出了一种可用于反舰导弹飞行试验安全分析并能取代弹道仿真的简化导航算法,对其实现原理和实现方法进行了阐述。经过实践检验,此种算法计算简单、效率高,其精度满足导弹飞行试验安全分析要求。     

考虑避免碰撞的编队卫星自适应协同控制

基于势函数法研究具有模型不确定性的编队飞行卫星避免碰撞的自适应协同控制.势函数法的思想为设计碰撞区域势函数值较大,所设计的控制律使得系统势函数具有减小的趋势,从而实现避免碰撞的编队飞行任务.首先,在无外部参考轨迹的情况下,通过引入避免碰撞势函数,提出一种自适应协同控制器,编队卫星最终实现速度一致和避免碰撞.进一步,考虑已知外部参考轨迹的情形,基于新的势函数方法,设计新的自适应协同控制器,能够同时实现避免碰撞、速度一致、卫星跟踪参考轨迹的目的.对于所提出的两种控制方法,均通过合理地应用Lyapunov稳定性理论分析了闭环系统的稳定性.仿真结果表明了所设计控制方法的有效性.     

The first results from the Herschel-HIFI mission

This paper contains a summary of the results from the first years of observations with the HIFI instrument onboard ESA’s Herschel space observatory. The paper starts by outlining the goals and possibilities of far-infrared and submillimeter astronomy, the limitations of the Earth’s atmosphere, and the scientific scope of the Herschel-HIFI mission. The presentation of science results from the mission follows the life cycle of gas in galaxies as grouped into five themes: Structure of the interstellar medium, First steps in interstellar chemistry, Formation of stars and planets, Solar system results and Evolved stellar envelopes. The HIFI observations paint a picture where the interstellar medium in galaxies has a mixed, rather than a layered structure; the same conclusion may hold for protoplanetary disks. In addition, the HIFI data show that exchange of matter between comets and asteroids with planets and moons plays a large role. The paper concludes with an outlook to future instrumentation in the far-infrared and submillimeter wavelength ranges.     

Exploration life support technology challenges for the Crew Exploration Vehicle and future human missions

As NASA implements the U.S. Space Exploration Policy, life support systems must be provided for an expanding sequence of exploration missions. NASA has implemented effective life support for Apollo, the Space Shuttle, and the International Space Station (ISS) and continues to develop advanced systems. This paper provides an overview of life support requirements, previously implemented systems, and new technologies being developed by the Exploration Life Support Project for the Orion Crew Exploration Vehicle (CEV) and Lunar Outpost and future Mars missions. The two contrasting practical approaches to providing space life support are (1) open loop direct supply of atmosphere, water, and food, and (2) physicochemical regeneration of air and water with direct supply of food. Open loop direct supply of air and water is cost effective for short missions, but recycling oxygen and water saves costly launch mass on longer missions. Because of the short CEV mission durations, the CEV life support system will be open loop as in Apollo and Space Shuttle. New life support technologies for CEV that address identified shortcomings of existing systems are discussed. Because both ISS and Lunar Outpost have a planned 10-year operational life, the Lunar Outpost life support system should be regenerative like that for ISS and it could utilize technologies similar to ISS. The Lunar Outpost life support system, however, should be extensively redesigned to reduce mass, power, and volume, to improve reliability and incorporate lessons learned, and to take advantage of technology advances over the last 20 years. The Lunar Outpost design could also take advantage of partial gravity and lunar resources.     

基于网络同步的航天器编队飞行姿态控制方法

航天器编队飞行需要协同控制系统进行统一的协调管理,以实现协同工作。文章将网络同步控制理论应用于航天器编队飞行姿态控制,以提高航天器编队飞行姿态控制的协同性。首先,采用修正的罗德里格斯参数描述航天器姿态动力学;然后,基于网络同步控制算法,设计航天器编队飞行的非线性姿态协同控制律;考虑成员航天器间姿态变化的差异,采用混合控制技术,设计航天器编队飞行混合控制策略。仿真结果验证了控制方法和控制律的有效性,并且相比单一反馈机制,混合控制具有更好的控制品质。     

多航天器编队在轨自主协同控制研究

提出一种基于信息一致性的分布式协同控制策略,该策略可自主实现多航天器编队 的 构型建立、保持与整体机动。在该策略中,编队内各航天器均具有局部的分层控制结构：参 考点一致性估计层根据各航天器初始状态与编队内信息拓扑,协商估计出多航天器编队整体 系统基准参考点;协同制导层根据编队整体系统模型预测控制方程,采用并行计算方式,规 划各航天器从初始状态到期望构型的期望重构机动路径;协同控制层采用基于二阶一致性算 法的协同反馈控制律,使各航天器彼此协同地跟踪期望路径和整体机动参考信息。仿真结果 表明:当信息拓扑中存在最大生成树时,该策略能够实现多航天器编队构型建立、保持与整 体机动的协同控制,并具有较好鲁棒性。〖JP〗