直升机若干关键技术发展研究

近年来,直升机技术表现出跨代发展特征,以总体设计、旋翼系统、传动系统、涡轴发动机、材料和制造技术、航电技术和飞控技术为代表的各技术领域均有较大突破,部分成果已得到应用.同时,高速旋翼机和无人直升机技术领域的发展也呈现出加速态势,在不久的将来将为直升机带来革命性的变革.     

GNSS global real-time augmentation positioning: Real-time precise satellite clock estimation,prototype system construction and performance analysis

Lots of ambiguities in un-differenced (UD) model lead to lower calculation efficiency, which isn’t appropriate for the high-frequency real-time GNSS clock estimation, like 1 Hz. Mixed differenced model fusing UD pseudo-range and epoch-differenced (ED) phase observations has been introduced into real-time clock estimation. In this contribution, we extend the mixed differenced model for realizing multi-GNSS real-time clock high-frequency updating and a rigorous comparison and analysis on same conditions are performed to achieve the best real-time clock estimation performance taking the efficiency, accuracy, consistency and reliability into consideration. Based on the multi-GNSS real-time data streams provided by multi-GNSS Experiment (MGEX) and Wuhan University, GPS + BeiDou + Galileo global real-time augmentation positioning prototype system is designed and constructed, including real-time precise orbit determination, real-time precise clock estimation, real-time Precise Point Positioning (RT-PPP) and real-time Standard Point Positioning (RT-SPP). The statistical analysis of the 6 h-predicted real-time orbits shows that the root mean square (RMS) in radial direction is about 1–5 cm for GPS, Beidou MEO and Galileo satellites and about 10 cm for Beidou GEO and IGSO satellites. Using the mixed differenced estimation model, the prototype system can realize high-efficient real-time satellite absolute clock estimation with no constant clock-bias and can be used for high-frequency augmentation message updating (such as 1 Hz). The real-time augmentation message signal-in-space ranging error (SISRE), a comprehensive accuracy of orbit and clock and effecting the users’ actual positioning performance, is introduced to evaluate and analyze the performance of GPS + BeiDou + Galileo global real-time augmentation positioning system. The statistical analysis of real-time augmentation message SISRE is about 4–7 cm for GPS, whlile 10 cm for Beidou IGSO/MEO, Galileo and about 30 cm for BeiDou GEO satellites. The real-time positioning results prove that the GPS + BeiDou + Galileo RT-PPP comparing to GPS-only can effectively accelerate convergence time by about 60%, improve the positioning accuracy by about 30% and obtain averaged RMS 4 cm in horizontal and 6 cm in vertical; additionally RT-SPP accuracy in the prototype system can realize positioning accuracy with about averaged RMS 1 m in horizontal and 1.5–2 m in vertical, which are improved by 60% and 70% to SPP based on broadcast ephemeris, respectively.     

“高分五号”全谱段相机可展开定标漫反射板设计

为了对“高分五号”卫星全谱段光谱成像仪的太阳反射谱段辐射性进行长期监测与校正，并针对其谱段范围宽、精度要求高、口径大、使用寿命长等特点与要求，优化设计了可展开的漫反射板进行全光路全视场的辐射定标。定标漫反射板安装在相机光学系统的前端侧面，不影响相机正常成像，在定标时通过驱动机构展开漫反射板到相机前端，根据“高分五号”卫星轨道特点、定标能量要求及相机安装矩阵等设计定标漫反射板展开角度为39°。研制了430mm×430mm大尺寸聚四氟乙烯漫反射板组件以保证在展开时满足全光路全视场的定标，漫反射板在420～2400nm光谱范围内半球反射率高于95%，在相机观测方向BRDF变化优于25%。同时，设计了漫反射板稳定性监视辐射计用于监测漫反射板在轨性能衰减，监测精度15%。在轨定标精度分析为476%，满足指标要求。     

导引头跟踪点跳变对制导精度影响分析

针对导弹正常制导过程中导引头跟踪点突变的情况,理论分析了导引头跟踪点突变对导弹过载指令的影响;对于不同的弹体动力学模型,仿真分析了跟踪点突变对制导系统精度的影响,并分析影响制导系统精度的主要相关因素;最后,探讨了跟踪点突变影响抑制方法。仿真分析表明,文中所述的方法能够有效抑制导引头跟踪点突变对制导精度的影响。     

等离子体对GPS信号载噪比的影响

飞行器再入过程产生等离子体,等离子体中电子密度的变化对电磁波信号造成幅度衰减和相位偏移,严重时导致通信中断。理论分析了等离子体对GPS信号载噪比的影响;利用实验室环境下的等离子体模拟装置,设计了GPS二键相控(BPSK)调制信号透过等离子体的地面模拟方案,进行了等离子体对GPS接收机性能影响的实验研究,获得了不同电子密度下的衰减和导航信号载噪比的数据。实验结果与理论分析一致,不仅证明了等离子体下衰减与导航信号载噪比的变化是一致的结论,而且验证了实验方法的有效性。     

Tangent-impulse transfer from elliptic orbit to an excess velocity vector

The two-body orbital transfer problem from an elliptic parking orbit to an excess veloc-ity vector with the tangent impulse is studied. The direction of the impulse is constrained to be aligned with the velocity vector, then speed changes are enough to nullify the relative velocity. First, if one tangent impulse is used, the transfer orbit is obtained by solving a single-variable function about the true anomaly of the initial orbit. For the initial circular orbit, the closed-form solution is derived. For the initial elliptic orbit, the discontinuous point is solved, then the initial true anomaly is obtained by a numerical iterative approach; moreover, an alternative method is proposed to avoid the singularity. There is only one solution for one-tangent-impulse escape trajectory. Then, based on the one-tangent-impulse solution, the minimum-energy multi-tangent-impulse escape trajectory is obtained by a numerical optimization algorithm, e.g., the genetic method. Finally, several examples are provided to validate the proposed method. The numerical results show that the minimum-energy multi-tangent-impulse escape trajectory is the same as the one-tangent-impulse trajectory.     

基于汇聚点观测的天基光学监视星座设计

针对地球静止轨道目标监视问题,提出了一种基于汇聚点观测的天基光学监视星座设计方法.研究分析了地球静止轨道目标分布特性,针对静止轨道目标在特定位置分布密度较大的特点,设计了监视星座对汇聚点区域进行重点观测的策略.分析了监视星座的轨道类型和传感器观测策略,提出采用太阳同步轨道设计监视星座和相应的汇聚点区域观测的方法.在满足对汇聚点观测要求及同步带重访周期为1d的条件下,对星座进行了设计.仿真结果表明：设计的4颗卫星组成的观测星座,对同步带目标的重访周期小于1d,24 h内的平均观测时间约为900 s,且能观测到更多的同步带目标.该方法可供工程应用参考.     

考虑卫星轨道运动和像移影响的星敏感器星图模拟方法

星图模拟技术是星图识别算法和星敏感器性能测试的基础.提出一种新的高精度星图模拟方法.该方法分为三个步骤:首先,利用两行轨道数据(TLE,Two-Line Orbital Element)与简化常规/深空扰动的近似解模型(SGP4/SDP4)计算出卫星在轨运行参数,进而获得卫星姿态矩阵;然后,根据星敏感器的方位和俯仰角度,确定星敏感器视场中的导航星及星敏感器安装矩阵,利用小孔成像模型,获得导航星在星敏感器成像面的投影位置;最后,为更准确模拟实际星像点的灰度扩散,在考虑卫星运动引起的恒星像移的基础上,按照二维高斯分布规律置灰度值来模拟星像点像素.在此基础上,还详细分析了不同曝光时间下,恒星像移对恒星位置测量的影响.     

一种适用于小推力轨控发动机“二次变轨”机动突防方案

针对突防发动机轨控推力较小,难以产生在拦截器末制导段内成功突防所需的机动过载的实际情况,提出避开拦截器机动性能最强的末制导段,而选择在拦截器自由飞行段和末制导结束后实施“二次机动变轨”的突防方案,旨在解决弹道中段机动突防方案的有效性问题.建立了推力方向、推力持续时间等轨控发动机主要控制参数的优化规划模型,提供了基于遗传...     

Impact of covariance information of kinematic positions on orbit reconstruction and gravity field recovery

Gravity missions are equipped with onboard Global Positioning System (GPS) receivers for precise orbit determination (POD) and for the extraction of the long wavelength part of the Earth’s gravity field. As positions of low Earth orbiters (LEOs) may be determined from GPS measurements at each observation epoch by geometric means only, it is attractive to derive such kinematic positions in a first step and to use them in a second step as pseudo-observations for gravity field determination. The drawback of not directly using the original GPS measurements is, however, that kinematic positions are correlated due to the ambiguities in the GPS carrier phase observations, which in principle requires covariance information be taken into account. We use GRACE data to show that dynamic or reduced-dynamic orbit parameters are not optimally reconstructed from kinematic positions when only taking epoch-wise covariance information into account, but that essentially the same orbit quality can be achieved as when directly using the GPS measurements, if correlations in time are taken into account over sufficiently long intervals. For orbit reconstruction covariances have to be considered up to one revolution period to avoid ambiguity-induced variations of kinematic positions being erroneously interpreted as orbital variations. For gravity field recovery the advantage is, however, not very pronounced.