Preparation and Properties of Smart Thermal Control and Radiation Protection Materials for Multi-functional Structure of Small Spacecraft

Considering the unique properties of small spacecraft,such as light weight,low power-consumption and high heat flux density,a new kind of lightweight boron carbide(B 4 C) radiation-protection coating material was proposed.New techniques for preparing LSMO thermal control coating and B 4 C radiation-protection coating were developed.The sample piece of multi-functional structure was manufactured by using the proposed materials,and a series of performance tests,such as thermal control and radiation-protection behaviors were evaluated.Test results show that:the emissivity of the multi-functional structure varies from 0.42 to 0.86 at 240 K to 353 K and the phase transition temperature is about 260 K.The electron radiation-protection ability of the multi-functional structure is 3.3 times better than that of Al material.The performance index of this multi-functional structure can meet the requirements for space application in on-board electronic equipment.     

Improvement of the Parameterized Identification Model Using Quasi-Steady and Nonuniform Inflow Aerodynamic Model

Compared with those of a fixed-wing aircraft, the dynamics of a rotorcraft are significantly more complex. One of the major challenges in the design of an autonomous helicopter is the development of a flight dynamic model, which can be useful for simulation studies and for the design of control law and navigational aspects. There is always a trade-off from the accuracy of the mathematical model to the more simplified model required for a control design as far as the helicopter rotor/fuselage dynamics is concerned. Small-scale helicopters posses a higher bandwidth of dynamics; hence, models developed from the first principle alone do not fulfill the needs, and more-sophisticated mathematical models are thus required. The main objective of the present work is to improve the parameterized identification model by replacing it with a most-general flight dynamic model for a minihelicopter. This model includes the rotor blade flap dynamics, stabilizer bar dynamics, and vehicle dynamics, which will be applicable for a general maneuvering flight. A systematic study is undertaken to analyze the influence of inflow models and flap response on the helicopter trim. Stability of the minihelicopter is also analyzed; except for phugoid, all other modes are stable in hover and high forward flight conditions.     

An architecture and protocol for communications satellite constellations regarded as multi-agent systems

This paper presents an architecture for satellites regarded as intercommunicating agents. The architecture is based upon a postmodern paradigm of artificial intelligence in which represented knowledge is regarded as text, inference procedures are regarded as social discourse and decision-making conventions, and the semantics of representations is grounded in the situated behaviour and activity of agents. A particular protocol is described for agent participation in distributed search and retrieval operations conducted as joint activities.     

Optimizing Launch‐on‐Time Probability

Future space projects such as space stations, large unmanned space structures, interplanetary spacecraft, and lunar and Mars bases will require highly reliable launch systems for their construction and logistic support. It may also be necessary to provide “guaranteed” commercial launches. These needs will place increased emphasis on mastering every aspect of launch‐vehicle operations, particularly a launch‐on‐time capability. Causes for delay during launch, i.e., unplanned “holds,” are attributable to several sources: weather, range activities, vehicle conditions, human performance, and so forth. In this paper, actual launch data on unscheduled hold distributions of various launch vehicles are presented. The data were supplied by industrial associate companies of the Center for Space Construction of the University of Colorado, Boulder. Probability models that can describe these historical data and be used for several purposes are determined: (1) As inputs to broader simulations of launch‐vehicle logistic space construction support processes; (2) to determine which launch operations sources cause the majority of the unscheduled holds; and (3) to suggest changes that might improve launch on time. The paper demonstrates the ability of a compound distribution probability model to fit the actual data. This model is then manipulated to develop a method for optimally improving launch‐on‐time probability.     

基于STK/X的远程导引变轨方案修正

远程导引多脉冲式变轨方案一般基于二体模型进行设计,设计结果存在摄动模型误差.当飞行时间较长时,由摄动模型误差带来的交会误差会达到上百公里甚至上千公里的量级,从而在实际摄动条件下难以实现追踪航天器和目标航天器的交会.采用L-BFGS-B优化算法,对初始的设计结果进行修正,以达到消除摄动模型误差的目的.优化过程中需要的真实摄动模型下的轨道预报,使用STK/X技术通过调用STK/Astrogator模块进行仿真得到.算例表明,初始设计的多脉冲式变轨方案经过修正后,能够在实际摄动条件下实现追踪航天器和目标航天器的交会.     

Research on Robust Control of Nonlinear Fuzzy VSS for Spacecraft

The nonlinear dynamic system of spacecraft with uncertainty and coupling is analyzed and its general dynamical equation is given. The decoupling-ability and controllability are proved. Aiming at this system, a new nonlinear decoupling controlling method is put forward by synthetically using the variable structure and fuzzy theory. The simulation results show that this method is effective in tracking performances under the existence of uncertainty and outer disturbance.     

Nonlinear receding horizon guidance for spacecraft formation reconfiguration on libration point orbits using a symplectic numerical method

This paper studies a nonlinear receding horizon control guidance strategy for spacecraft formation reconfiguration on libration orbits in the Sun–Earth system. For comparison, a linear quadratic soft terminal control strategy is also considered for the same reconfiguration missions. A novel symplectic iterative numerical algorithm is proposed to obtain the optimal solution for the nonlinear receding horizon control strategy at each update instant. With the aid of the quasilinearization method, a high-efficiency structure-preserving symplectic method is introduced in the iterations, and the optimal control problem is replaced successfully by a series of sparse symmetrical linear equations. Several typical spacecraft formation reconfiguration missions including resizing, rotating and slewing reconfigurations and their combinations are numerically simulated to show the effectiveness of the nonlinear receding horizon guidance strategy based on the proposed symplectic algorithm. Through these simulations, the nonlinear receding horizon control strategy is shown to have obvious advantages in convergence and parameter sensitivity compared with a linear quadratic soft terminal control strategy. Monte Carlo stochastic simulations are used to test the robustness of the nonlinear receding horizon control guidance in dealing with measurement and execution errors.     

神舟飞船关键链项目管理贝叶斯网络模型

在研究关键链项目管理和贝叶斯网络技术的基础上,结合神舟飞船项目进度管理的特点,建立了神舟飞船关键链项目管理贝叶斯网络模型.首先详细描述了如何将关键链中的每个工序按照时间和资源约束的条件分解成贝叶斯网络模型中的6个节点,并进一步简化为4个节点.然后,以神舟飞船研制网络计划图为依据,说明了关键链项目管理贝叶斯网络模型的建立过程.最后,基于贝叶斯网络推理成功识别出影响神舟飞船项目进度推迟的关键工序.     

Finite element design of manipulator-coupled spacecraft for a research testbed

This paper describes the design and analysis of a research testbed developed to study the control of manipulator-coupled spacecraft with independent attitude control systems. This scenario could present itself in the assembly of Space Station Freedom (SSF). SSF assembly calls for a rendezvous of the Space Shuttle (SS) with SSF. Part of the assembly process requires that both spacecraft be coupled via the Space Shuttle Remote Manipulator System. An additional criterion that poses increased complexity is that the Space Shuttle controls and Space Station controls can not communicate. The technical issue involved is unwanted vibrations of the coupled-configuration that occur retraction and the complications due to non-interacting control systems. To understand these vibrations and possible complications, a research testbed has been built at the Marshall Space Flight Center in Huntsville, AL.To build the testbed, the manipulator links joints, and vehicles that represent the Space Shuttle and Space Station had to be designed. Pre-design simulation studies using ANSYS [1] (a Finite Element Computer Code) is used to size and design the manipulator links for the experimental facility. The ANSYS results were verified by the development of the Lagrangian Equations of motion. The Harmonic drives used as joints for the two link, three joint manipulator have been dissected into free body diagrams to ensure proper load paths in the ANSYS models. Accurate simulation of manipulator-coupled spacecraft is an important technology for NASA to understand. This paper outlines the methodology behind the preliminary design of a research testbed developed to help NASA gain knowledge in this area.     

Development of a Centrifugal Oil Lubricator for Long-Term Lubrication of Spacecraft Attitude Control Systems—Experimental Evaluation

The success of a spacecraft mission depends to a great extent on the performance of the moving mechanical systems. The most common mode of failure in these systems is tribological. Tribological failures occur mainly due to nonavailability of lubricant at the working zone of the bearings as a result of degradation, evaporation, and creep. The life of these moving mechanical systems could be extended if lubricant is replenished by some means. Therefore, to ensure long-term uninterrupted performance of these systems, an efficient lubricant replenishment system is essential. This article describes the development of a novel lubricant supply system that can supply lubricant for more than 30 years at a controlled rate of a few micrograms/hour. Experimental evaluation of the lubricator was carried out under different operating conditions experienced in a spacecraft. The results of the experiments are compared with the theoretical results obtained from the mathematical model and computational fluid dynamics (CFD) simulation. The lowest flow rate obtained was 3.5 μg/h from a lubricator with a flow control orifice diameter of 2.3 μm. The results of the study show that the lubricator can provide a long-term uninterrupted supply of lubricant to the moving mechanical systems for a period of more than 30 years. An outstanding and most promising feature of this lubricator is that the flow rate at various stages of the life can be theoretically predicted using the developed mathematical model and the prediction can be experimentally verified before the system is put into service.