Inverse free steering law for small satellite attitude control and power tracking with VSCMGs

Recent developments in integrated power and attitude control systems (IPACSs) for small satellite, has opened a new dimension to more complex and demanding space missions. This paper presents a new inverse free steering approach for integrated power and attitude control systems using variable-speed single gimbal control moment gyroscope. The proposed inverse free steering law computes the VSCMG steering commands (gimbal rates and wheel accelerations) such that error signal (difference in command and output) in feedback loop is driven to zero. H_∞ norm optimization approach is employed to synthesize the static matrix elements of steering law for a static state of VSCMG. Later these matrix elements are suitably made dynamic in order for the adaptation. In order to improve the performance of proposed steering law while passing through a singular state of CMG cluster (no torque output), the matrix element of steering law is suitably modified. Therefore, this steering law is capable of escaping internal singularities and using the full momentum capacity of CMG cluster. Finally, two numerical examples for a satellite in a low earth orbit are simulated to test the proposed steering law.     

提高光学遥感卫星图像几何精度总体设计分析

针对如何提高我国光学遥感卫星图像几何定位精度问题,从影响几何成像质量的关键要素——内外方位元素出发,介绍地面几何处理方法,并基于多颗卫星研制、地面量测试验及在轨验证情况,对高分辨率光学遥感卫星和多线阵观测卫星的几何精度的星-地全链路影响误差项进行对比分析,通过理论分析找出了约束我国高分辨率遥感卫星几何精度的关键问题,最后探讨了如何通过星上设计配合地面处理提高高分辨率遥感卫星的几何精度。     

一种针对分离模块航天器系统的分层优化方法

针对分离模块航天器系统优化中存在计算量大、算法复杂度高的问题,提出了一种基于分层的分离模块航天器系统优化方法。该方法将系统优化问题分解为三个层次进行,顶层规划模块数和轨道高度,中间层优化组件配置,底层优化运载发射方案。其中顶层嵌套调用中间层,中间层嵌套调用底层,底层直接计算求解最优运载发射方案,避免了直接基于分离模块航天器全寿命周期仿真来优化运载发射方案。应用该方法对虚拟对地遥感分离模块航天器进行优化,结果表明,优化过程简单,计算量小,算法复杂度低,优化效果显著。     

星载低复杂度Turbo译码器的实现技术研究

针对航天测控通信系统中微弱信号处理的实际应用需求,研究了Turbo译码算法在星载平台上的低复杂度实现技术。基于折线近似的Log_MAP算法,提出了一种新的基于FPGA的译码器实现方案,一方面简化了迭代译码过程中分支度量的计算存储方法,有效减少了存储容量及算法复杂度;另一方面采用半并行化及流水的数据处理方式,提高了译码处理速度。利用CCSDS标准建议的交织器和生成矩阵进行了仿真和实测,结果表明相较于其它结构,采用本文设计方案实现的Turbo译码器在Slice资源没有增加的条件下存储复杂度降低了29.6%,且在输出误码率<10 -6 时编码增益达到了9.9dB,保持了良好的译码性能。本文译码器已成功应用于某航天型号工程。     

中长期轨道预报中大气阻力系数补偿算法的研究

利用地磁平静期的CHAMP卫星精密星历对多个弧段的大气阻力系数进行解算,找到了适用于轨道预报的最优系数,分析了最优阻力系数与地磁指数、迹向残差的关系,利用线性回归分析建立了大气阻力系数补偿算法。针对中长期轨道预报的需求,该算法能够降低定轨弧段较短条件下阻力系数的解算误差。将该补偿算法应用于不同时期CHAMP卫星和天宫一号的轨道预报,验证了该算法的正确性和普遍适用性,结果表明预报精度能够提高20%以上。     

气闸舱泄复压热力过程研究

为满足航天员出舱活动的需要,出舱活动飞船气闸舱在满足载人飞船密封舱一般要求外,还需经历泄压和复压两个热力过程。伴随气闸舱的泄复压过程,舱内空气因泄压而发生热力膨胀降温现象,因复压而出现热力压缩升温现象;复压用气瓶在气闸舱复压过程中压力急剧降低也出现降温现象,其降温程度将影响气闸舱复压后舱内温度水平。运用热力学方法对气闸舱泄复压热力过程进行分析,并通过地面和在轨飞行试验验证了分析的正确性,本文工作将为后续载人航天器气闸舱的热控设计提供参考。     

地月平动点拟周期轨道探测器自主导航方法研究

地月L2点的拟周期轨道可以用于实现与月球背面的持续通信,具有重要的科学研究价值和广阔的应用前景。针对地月L2点探测器所处的弱稳定拟周期轨道,论证了基于日地月信息的自主导航方法的可行性,并进行了深入分析。首先,推导了会合坐标系下带有星历的精确导航动力学方程;其次,针对弱稳定轨道不同于近地强稳定轨道的特性,在基于日地月方位信息导航的基础上,提出了三种敏感器组合方案。使用迭代最小二乘方法给出导航仿真结果,并结合非线性可辨识性理论对这三种情况下历元状态的可辨识性及可辨识度进行分析。最后,仿真结果表明,使用日地月敏感器以及对地多普勒雷达可以满足历元状态的可辨识性、导航的收敛性以及系统经济性的要求。     

Severe disruption of the cytoskeleton and immunologically relevant surface molecules in a human macrophageal cell line in microgravity—Results of an in vitro experiment on board of the Shenzhou-8 space mission

During spaceflight the immune system is one of the most affected systems of the human body. During the SIMBOX (Science in Microgravity Box) mission on Shenzhou-8, we investigated microgravity-associated long-term alterations in macrophageal cells, the most important effector cells of the immune system. We analyzed the effect of long-term microgravity on the cytoskeleton and immunologically relevant surface molecules. Human U937 cells were differentiated into a macrophageal phenotype and exposed to microgravity or 1g on a reference centrifuge on-orbit for 5 days. After on-orbit fixation, the samples were analyzed with immunocytochemical staining and confocal microscopy after landing. The unmanned Shenzhou-8 spacecraft was launched on board a Long March 2F (CZ-2F) rocket from the Jiuquan Satellite Launch Center (JSLC) and landed after a 17-day-mission. We found a severely disturbed actin cytoskeleton, disorganized tubulin and distinctly reduced expression of CD18, CD36 and MHC-II after the 5 days in microgravity. The disturbed cytoskeleton, the loss of surface receptors for bacteria recognition, the activation of T lymphocytes, the loss of an important scavenger receptor and of antigen-presenting molecules could represent a dysfunctional macrophage phenotype. This phenotype in microgravity would be not capable of migrating or recognizing and attacking pathogens, and it would no longer activate the specific immune system, which could be investigated in functional assays. Obviously, the results have to be interpreted with caution as the model system has some limitations and due to numerous technical and biological restrictions (e.g. 23 °C and no CO₂ supply during in-flight incubation). All parameter were carefully pre-tested on ground. Therefore, the experiment could be adapted to the experimental conditions available on Shenzhou-8.     

载荷—火箭分离导向机构参数设计及动力学分析

针对载荷—火箭分离中易碰撞以及载荷部姿态的问题,以多体系统动力学理论为基础,在ADAMS中建立了针对一种新型分离导向机构的载荷—火箭分离虚拟样机模型,分别就分离导向机构支柱刚度、高度、滚轮与载荷部之间预载对分离结果的影响进行了计算分析。结果表明：刚度与高度的取值越大,分离过程中的分离最小间隙就越大,越有利于火箭与载荷部的成功分离;预载主要影响载荷部的姿态。基于此结果,设计了一套分离导向机构的匹配参数,并结合姿态控制律,利用ADAMS与Simulink软件包进行联合仿真,校验了这套设计参数可以保证火箭与载荷部的正常分离,姿控系统可以纠正载荷部的姿态偏差。本文采用的研究方法以及所获得的结论对采用该形式分离导向装置的载荷—火箭分离问题具有普适性。     

类HTV-2横侧向稳定性研究

针对HTV-2类飞行器存在的横侧向稳定性差的问题,通过风洞试验、模态分析和参数敏感性分析方法研究了类HTV-2飞行器的横侧向稳定性。研究结果表明：与偏航方向相比,滚转静、动稳定性都更弱,表现为：攻角小于10°滚转方向是静不稳定的;在滚转动态试验中,振动曲线随时间不是呈现收敛趋势,而是出现明显非线性多频谱周期性特征。通过在模型前体布置顺气流纵向绊线促使流动对称转捩的方法,增加了滚转曲线的线性和横侧向稳定性。横侧向模态和参数敏感性分析表明,滚转模态随时间缓慢发散,系统对偏航静稳定性等参数比较敏感。