Method of virtual trajectories for the design of gravity assisted missions

A method of virtual trajectories is proposed for the design of multiple gravity assist trajectories. The method comprises two principal stages. First, for a chosen planetary sequence, a database of virtual trajectories is tabulated. Then the database screening and refinement are performed. The design of trajectory to Jupiter is presented.     

Reachable domain of spacecraft with a single tangent impulse considering trajectory safety

The reachable domain of the two-body transfer orbit with a single upper-bounded tangent impulse is studied. Three cases are analyzed for either the magnitude of the tangent impulse or the initial impulse point being free, or both being free. For a fixed impulse magnitude and a free initial impulse point, the initial orbit is proved to be one of the envelopes of the reachable domain. Moreover, the trajectory safety for the transfer orbit requires a lower bound on the perigee altitude and an upper bound on the apogee altitude. Then the ranges of the impulse magnitude and the initial true anomaly can be obtained by solving quadratic and cubic inequalities, respectively. If both constraints are required for an arbitrary impulse point, the range of the impulse magnitude is obtained with impulses at the perigee and the apogee. Several numerical examples with different eccentricities are provided to show the geometry of the reachable domain and to verify the proposed method.     

应用模糊变权的启发式搜索进行飞行轨迹优化

回顾了军机轨迹优化问题的提出及研究历史，介绍了几种主要方法的特点，特别是启发式搜索算法应用于飞行轨迹优化问题时存在的主要问题。提出为了得到较好的近优路径而采取的模糊变权处理方法。通过计算不同加权下解的情况，说明模糊变权方法是使加权随具体情况作相应调整的有效手段，为提高飞行路径规划系统的有效性开辟了一个新思路。     

弹道修正执行机构综述

二维弹道修正弹是一种低成本、高精度的精确打击弹药,修正机构是弹道修正弹上的重要部件,其性能决定了弹丸的弹道修正能力。针对弹道的二维修正需求,介绍了国内外对二维弹道修正弹修正机构的研究状况;列举了应用在二维弹道修正弹上不同类型的修正机构;阐述了不同类型修正机构的工作原理、特点以及各自的局限性。最后,对不同类型修正机构特性进行了比较,给出了相关技术指标,对比了各自的优缺点。阐述了选择和设计执行机构应注意的问题。     

Disturbance observer based model predictive control for accurate atmospheric entry of spacecraft

Facing the complex aerodynamic environment of Mars atmosphere, a composite atmospheric entry trajectory tracking strategy is investigated in this paper. External disturbances, initial states uncertainties and aerodynamic parameters uncertainties are the main problems. The composite strategy is designed to solve these problems and improve the accuracy of Mars atmospheric entry. This strategy includes a model predictive control for optimized trajectory tracking performance, as well as a disturbance observer based feedforward compensation for external disturbances and uncertainties attenuation. 500-run Monte Carlo simulations show that the proposed composite control scheme achieves more precise Mars atmospheric entry (3.8?km parachute deployment point distribution error) than the baseline control scheme (8.4?km) and integral control scheme (5.8?km).     

关于外测新体制的一些分析与思考

针对外测新体制下数据处理中遇到的一些重要问题进行了较为深入的讨论。认真分析了多站测速系统的严重病态以及样条约束的EMBET算法在目标非平稳段的剩余截断误差等制约弹道处理精度的重要问题,并提出解决问题的思路与方法。     

A multi-aircraft conflict detection and resolution method for 4-dimensional trajectory-based operation

Conflict Detection and Resolution(CDR) is the key to ensure aviation safety based on Trajectory Prediction(TP). Uncertainties that affect aircraft motions cause difficulty in an accurate prediction of the trajectory, especially in the context of four-dimensional(4D) Trajectory-Based Operation(4DTBO), which brings the uncertainty of pilot intent. This study draws on the idea of time geography, and turns the research focus of CDR from TP to an analysis of the aircraft reachable space constrained by 4D waypoint constraints. The concepts of space–time reachability of aircraft and space–time potential conflict space are proposed. A novel pre-CDR scheme for multiple aircraft is established. A key advantage of the scheme is that the uncertainty of pilot intent is accounted for via a Space-Time Prism(STP) for aircraft. Conflict detection is performed by verifying whether the STPs of aircraft intersect or not, and conflict resolution is performed by planning a conflict-free space–time trajectory avoiding intersection. Numerical examples are presented to validate the efficiency of the proposed scheme.     

Backstepping sliding-mode control of stratospheric airships using disturbance-observer

In the presence of unknown disturbances and model parameter uncertainties, this paper develop a nonlinear backstepping sliding-mode controller (BSMC) for trajectory tracking control of a stratospheric airship using a disturbance-observer (DO). Compared with the conventional sliding mode surface (SMS) constructed by a linear combination of the errors, the new SMS manifold is selected as the last back-step error to improve independence of the adjustment of the controller gains. Furthermore, a nonlinear disturbance-observer is designed to process unknown disturbance inputs and improve the BSMC performances. The closed-loop system of trajectory tracking control plant is proved to be globally asymptotically stable by using Lyapunov theory. By comparing with traditional backstepping control and SMC design, the results obtained demonstrate the capacity of the airship to execute a realistic trajectory tracking mission, even in the presence of unknown disturbances, and aerodynamic coefficient uncertainties.     

Contingency target assessment,trajectory design,and analysis for NASA’s NEA scout solar sail mission

The presented study examines contingency target selection and trajectory design for NASA’s Near-Earth Asteroid Scout mission under the assumption of a missed lunar gravity assist. Two previously considered asteroids are selected as potential targets for the given scenario based on favorable orbital characteristics for launch dates ranging from June 27, 2020 through July 26, 2020. Initially, a simplified circular restricted 3-body problem + ideal solar sail model is utilized to survey trajectory options for a month-long launch window. Selected solutions from this data set are then converged in an N-body ephemeris + non-ideal sail model. Results suggest that NEA Scout can still perform asteroid rendezvous mission under the missed lunar gravity assist scenario with new targets, 2019 GF1, 2018 PK21, and 2007 UN12, based on the target launch dates. Further target assessment is carried out for 165 days beyond the current June 27, 2020 launch date.     

用RTR技术确定SRM燃烧室凝相粒子加入边界条件

由于缺乏有效的实验手段, 目前的ＳＲＭ 颗粒轨道模型很不完善, 其中粒子的加入边界条件完全是建立在人为假设的基础上。针对这种情况, 发展了一种以实验为基础的确定凝相粒子加入边界条件的方法, 首先利用ＲＴＲ技术对实验发动机热试车条件下凝相粒子的运动进行实验研究, 通过图象处理技术获得粒子的运动轨迹, 然后采用轨道模型法计算实验条件下凝相粒子的运动轨迹, 通过轨迹反推法给出了粒子加入边界条件。