解析计算在月球中继卫星Halo轨道设计中的应用

面向月球中继卫星工程轨道设计需求,研究解析计算方法在地月系L2点halo轨道设计中的应用问题。在讨论圆型限制性三体问题三阶解析近似计算方法的基础上,分析了解析计算与数值计算的差异,给出了解析近似计算在工程约束下的适用范围,进而提出了基于解析计算的轨道设计和特征筛选方法。分别采用解析初值和数值初值进行halo轨道外推,比对验证采用解析计算设计轨道的可行性。研究结果表明,解析计算方法适用于月球中继卫星轨道的初步设计、特征分析和构型筛选。     

国内民航客运需求价格点弹性与弧弹性研究

采用微观经济学的点弹性和弧弹性理论,对国内民航客运需求价格弹性进行初步对比研究.结合民航客运的自身特点,提出适用于民航客运需求价格弹性的点弹性和弧弹性分析方法,并采用此方法对国内民航客运市场进行分析,得出国内民航整体市场是富于弹性的和旺盛需求的结论,最后给出点弹性与弧弹性对比.     

运输机空投起始点研究

根据货物空投着陆点及空投轨迹,计算出运输机空投起始点,并将所计算的空投起始点信息提供给航电系统,引导运输机执行空投点航线。空投起始点的研究对运输机实现空投功能及提高空投精度具有重要的理论意义和现实意义。     

一种利于交班的舰空导弹最优中制导律设计

针对舰空导弹超视距拦截低空飞行目标问题,在复合制导的中制导段,建立了导弹拦截目标的相对运动模型,依据制导平台无线电指令修正信息,考虑舰空导弹拦截低空目标时的飞行速度特性,给出了预测遭遇点的实时解算模型,并确定了利于中末制导交班的中制导终端约束条件。基于拦截预测遭遇点,引入伪控制量的概念,应用线性二次型最优控制理论,设计了一种基于拦截预测遭遇点的利于制导交班的最优中制导律,仿真结果验证了预测遭遇点实时解算模型和最优中制导律的正确性与有效性。     

Libration point orbits for lunar global positioning systems

With the development of lunar exploration, a lunar global positioning system (LGPS) is demanded for both on-ground and in-flight lunar exploration missions. The traditional configuration of constellation requires at least eighteen satellites to cover the whole lunar surface continuously. In this paper, the configurations of the libration point orbits (LPOs) constellations are investigated. By using the constellations on the Earth–Moon _L1$L_1$ and _L2$L_2$ LPOs, the basic functions of the LGPS can be realized by using eight to fourteen satellites. First, the LPO and the combinations of LPOs, which can be used in the constellations of the LGPS, are investigated. The criteria and procedures of the configuration design are introduced. Second, the configurations of LPOs constellations are investigated in the Earth–Moon circular-restricted three-body problem (CR3BP). The size of the LPOs and the distribution of the satellites on these LPOs are determined by using an exhaustive algorithm and a global optimization method, respectively. The key performance parameters of these constellations are computed. Third, the constellations with good performance in the CR3BP are redesigned in the more accurate Earth–Moon based Sun-perturbed bicircular four-body problem (B4BP). Moreover, in order to avoid the ground coverage problem caused by the perturbation of the Sun, some modifications are implemented, and the configuration of the no blind area LGPS in the B4BP is obtained.     

Symmetry and asymmetry of ionospheric weather at magnetic conjugate points for two midlatitude observatories

Variations of the ionospheric weather W-index for two midlatitude observatories, namely, Grahamstown and Hermanus, and their conjugate counterpart locations in Africa are studied for a period from October 2010 to December 2011. The observatories are located in the longitude sector, which has consistent magnetic equator and geographic equator so that geomagnetic latitudes of the line of force are very close to the corresponding geographic latitudes providing opportunity to ignore the impact of the difference of the gravitational field and the geomagnetic field at the conjugate points on the ionosphere structure and dynamics. The ionosondes of Grahamstown and Hermanus provide data of the critical frequency (foF2), and Global Ionospheric Maps (GIM) provide the total electron content (TECgps) along the magnetic field line up to the conjugate point in the opposite hemisphere. The global model of the ionosphere, International Reference Ionosphere, extended to the plasmasphere altitude of 20,200 km (IRI-Plas) is used to deliver the F2 layer peak parameters from TECgps at the magnetic conjugate area. The evidence is obtained that the electron gas heated by day and cooled by night at the summer hemisphere as compared with the opposite features in the conjugate winter hemisphere testifies on a reversal of plasma fluxes along the magnetic field line by the solar terminator. The ionospheric weather W-index is derived from NmF2 (related with foF2) and TECgps data. It is found that symmetry of W-index behavior in the magnetic conjugate hemispheres is dominant for the equinoxes when plasma movement along the magnetic line of force is imposed on symmetrical background electron density and electron content. Asymmetry of the ionospheric storm effects is observed for solstices when the plasma diffuse down more slowly into the colder winter hemisphere than into the warmer summer hemisphere inducing either plasma increase (positive phase) or decrease (negative phase of W-index) in the ionospheric and plasmaspheric plasma density.     

一种弹目遭遇点预测方法

为充分利用舰空导弹中制导段所获信息并减小导弹中制导段的弹道曲率,给出一种弹目预测遭遇点的解算方法,并据此设计比例导引制导律。在初始发射坐标系中,假设目标由当前位置以当前速度大小沿当前速度方向匀速运动至遭遇点,导弹由当前位置以当前速度大小按照一定的导引规律匀速运动至遭遇点。在该假设条件下,导弹到达遭遇点的总航路大小一方面...     

小推力航天器的地月低能转移轨道

 在限制性四体模型下研究基于小推力方式的地月低能转移问题,通过借助于平动点轨道的相空间结构来揭示小推力转移的机理。重点研究了小推力转移自由飞行段的构造：经由LL₁点穿越获得最小能量的低能转移;而经由LL₁点Halo轨道穿越,得到(M,N)圈穿越轨道;由于Halo轨道相对于平动点增加了一维度的选择,根据(2,2)圈穿越轨道构造该转移的自由飞行段。在地球势阱逃逸和月球势阱捕获段,分别设计了合适的小推力的控制律及发动机开/关机时间,成功实施近地球段的小推力加速和近月球段的减速。尽管未对所得到的结果进行优化,所得转移轨道的燃料消耗也与类似边界条件的SMART-1轨道基本一致。     

基于标准弹道点的最优制导方法

由于基于需要速度的显式制导方法要确定虚拟目标点,虚拟目标点的确定要对地球扁率和再入阻力的影响进行修正,存在着百米以上的修正误差,为此提出了基于标准弹道点的最优制导方法,即将标准弹道的某点作为目标点进行需要椭圆轨道计算及最优入轨控制。提供了采用弹上迭代制导方法实现最优控制,同时给出了预测关机参数的需要椭圆轨道终端约束校正方法。该制导方法无需进行地球扁率和再入阻力的影响修正,可以减少方法误差,仿真计算证明了这一点。     

结构可靠性分析的拟蒙特卡罗方法

由于蒙特卡罗(MC)方法具有程序结构简单,收敛速度与问题维数无关等优点,故其在结构可靠性分析中得到了广泛应用。但是对于小失效概率等问题,计算效率低这一主要缺点限制了该方法的应用范围。为了解决MC方法存在的问题,通过引进单位超立方体中不同的低偏差点集代替伪随机数序列,并结合了重要抽样技术建立了结构可靠性分析的拟蒙特卡罗(QMC)方法。该方法不但可以大幅度减少抽样点数目,还能够得到确定性的估计值, 避免传统MC方法只能得到概率意义下误差的缺陷。通过数值算例可以看出本文方法具有较高的计算精度和效率,因此适用于结构可靠性分析问题。