北斗/GPS双频载波相位单点定位模型及精度分析

针对海洋工程实时米级绝对定位需求,利用双频伪距、载波相位观测量和同时估计接收机位置、接收机钟差和载波相位模糊度,构建了一种双频载波相位实时单点定位方法.亚太区域14个测站试验结果显示:北斗水平和高程定位RMS分别为1.33m和1.81m,GPS为0.60m和0.85m,北斗/GPS组合为0.56m和0.72m;船载动态...     

Indirect optimization for finite thrust orbit transfer and cooperative rendezvous using an initial guess generator

In this paper, the finite thrust nonplanar transfer and cooperative rendezvous are investigated. The indirect method is adopted in the optimization process. The energy-optimal to fuel-optimal continuation is performed by using the homotopy method. An initial guess generator (IGG) is designed based on a simplified dynamical model to overcome the difficulty in providing the initial guess. Some reasonable simplifications on the dynamical model are applied based on the near-circular near-coplanar transfer. The initial guess can be obtained by analytically solving a system of linear equations. Therefore, the IGG has high computational efficiency. Moreover, the terminal time and state are estimated by IGG to deal with the cooperative rendezvous problem. Numerical examples are presented and the validity of the “IGG-Homotopy” combined algorithm is verified.     

BeiDou-3 orbit and clock quality of the IGS Multi-GNSS Pilot Project

Within the Multi-GNSS Pilot Project (MGEX) of the International GNSS Service (IGS), precise orbit and clock products for the BeiDou-3 global navigation satellite system (BDS-3) are routinely generated by a total of five analysis centers. The processing standards and specific properties of the individual products are reviewed and the BDS-3 orbit and clock product performance is assessed through direct inter-comparison, satellite laser ranging (SLR) residuals, clock stability analysis, and precise point positioning solutions. The orbit consistency evaluated by the signal-in-space range error is on the level of 4–8 cm for the medium Earth orbit satellites whereas SLR residuals have RMS values between 3 and 9 cm. The clock analysis reveals sytematic effects related to the elevation of the Sun above the orbital plane for all ACs pointing to deficiencies in solar radiation pressure modeling. Nevertheless, precise point positioning with the BDS-3 MGEX orbit and clock products results in 3D RMS values between 7 and 8 mm.     

Improving the low orbit satellite tracking ability using nonlinear model predictive controller and Genetic Algorithm

The satellite motion on the reference orbit (RO) with less energy consumption has always persuaded researchers to design optimal control systems. The nonlinear nature and time-varying equations of motion make this quest more challenging. The present study proposes a novel control system for satellite motion on the RO by considering a comprehensive model of its dynamics in orbit and a Nonlinear Model Predictive Controller (NMPC). The NMPC calculates the sub-optimal control inputs of satellite motion reference on the elliptic orbit by minimizing a convex cost function at each stage. Moreover, all weighting parameters of the cost function are optimized by the Genetic Algorithm (GA) to produce less perturbation and guarantee the best NMPC performance. Finally, the implemented NMPC has been compared to a Linear MPC (LMPC). The results show that not only can the NMPC resist against larger errors and perturbations, but it can also compensate for those errors by returning the satellite to its main orbit and maintaining it.     

Error modeling and compensating of a novel 6-DOF aeroengine rotor docking equipment

In the docking process of aeroengine rotor parts, docking accuracy that indicates the gaps between the end faces is strictly required. A key issue is improving docking accuracy using automated docking equipment. In this paper, a systematic study is carried out on the error modeling and compensation of a novel six-degrees-of-freedom(6-DOF) docking equipment for aeroengine rotors. First, a new model for indicating the main indexes of docking accuracy is proposed. Then, the error model of a special...     

利用姿态机动的绳系卫星编队系统轨道协同控制

为克服绳系卫星编队系统在轨道机动过程中的系绳摆动现象，提出一种通过调整领航星推力方向进而实现编队系统轨道跟踪的控制算法。由于推力方向角与状态量互相耦合且少于系统自由度个数，轨道协同控制属于典型的非仿射欠驱动控制问题。针对此问题，首先采用升阶法将角速度作为虚拟控制输入；然后为各子系统设计子滑模面后加权得到高层滑模面和等效控制输入律，并设计观测器估计系统非线性项；其次基于模型预测控制算法优化得到最高层滑模面的趋近控制律；最后采用MATLAB/Simulink验证了所提控制算法的有效性。     

An atmosphere-breathing propulsion system using inductively coupled plasma source

CubeSats have attracted more research interest recently due to their lower cost and shorter production time. A promising technology for CubeSat application is atmosphere-breathing electric propulsion, which can capture the atmospheric particles as propulsion propellant to maintain long-term mission at very low Earth orbit. This paper designs an atmosphere-breathing electric propulsion system for a 3 U CubeSat, which consists of an intake device and an electric thruster based on the inductively coupled plasma. The capture performance of intake device is optimized considering both particles capture efficiency and compression ratio. The plasma source is also analyzed by experiment and simulation. Then, the thrust performance is also estimated when taking into account the intake performance. The results show that it is feasible to use atmosphere-breathing electric propulsion technology for CubeSats to compensate for aerodynamic drag at lower Earth orbit.     

有限元仿真模型V&V技术研究

仿真模型建模过程存在多种误差输入，将引起仿真预测结果的不精确性。采用仿真模型V&V（Verification and Validation,验证与确认）技术，进行仿真模型的建模误差分析与控制。利用物理试验数据进行仿真模型的精度评估，基于模型修正算法进行仿真建模参数的自动修正，提升仿真和试验结果的一致性，帮助设计师基于精确的仿真模型进行产品的虚拟性能预示，提升仿真技术在产品研制流程中的地位和作用。阐述了模型V&V的概念和流程，对模型V&V的关键技术和原理进行了详细论述,以NASA Rotor37转子验模为例进行了V&V案例说明。