Equilibrium positions of a weight on a cable fixed to a dumbbell-shaped space station moving along a circular geocentric orbit

The motion of a space object in the gravitational field of the Earth is considered. The object consists of an extended space station and a weight, which is free to move along the cable fixed to the ends of the station. It is assumed that the station is composed of two masses coupled by a weightless rod, while the cable is weightless and non-stretched. The equations of motion of such a system are derived for the case when the motion proceeds in a single plane, while the center of mass of the system moves along a circular geocentric orbit. The conditions of the cable tension (conditions of being on tie) are derived. The phase portrait of the weight motion along the cable is constructed when the station is oriented to the attracting center or is perpendicular to this position. The possibility to leave the tie in this case is analyzed. Equilibrium configurations of the system are found, i.e., such motions of the object under consideration at which the weight does not change its position relative to the station. Lyapunov stability of such configurations is analyzed for two situations: when the station is composed of equal masses and when masses at the ends of the station are different. In particular, for the case of different masses it is established that there exist such positions of equilibrium at which the dumbbell is located at an angle to the direction to the attracting center. In some cases these positions can be stabilized (if the weight is fixed on the cable).     

Force on a coil moving above a grid structure

The force on a coil moving with a high-speed parallel to a conducting grid consisting of parallel tubes is investigated. The coil performs a rebound motion or an oscillatory heave motion when pressed toward the grid by reactive on-board engines. The coil is approximated by two parallel wires moving parallel to the grid tubes. The corresponding electrodynamic problem is two dimensional and is solved by expansions in terms of Bessel functions. Expressions are derived for the lift and drag force as well as the heat generated in the tubes in the limit of strong skin effect. The dependence on the grid spacing is analysed in the approximation of no mutual inductance between the tubes. Two specific applications are a shunt deflecting the coil, and a funnel leading to multiple reflection. Finally, the varying magnetic flux threading the coil is considered and the thermal load of the coil is estimated.     

Optimal Control of a Programmed Turn of a Spacecraft

A problem of optimal turn of a spacecraft is considered. The time of turn is minimized, as well as the functional having a meaning of the propellant consumption. An analytical solution to the problem stated is derived. It is demonstrated that the solution optimal in this sense belongs to a class of two-impulse controls, under which a spacecraft executes the turn along the trajectory of its free motion. The solution obtained in this paper differs from earlier available solutions considerably. The estimations of the propellant consumption for a realization of the programmed turn are made.     

一个带间隙连接结构对梁基频漂移影响研究

文章以一端夹支、另一端带套筒连接结构的梁作为研究对象,通过在连接结构中引入间隙非线性因素,分别研究了在连接结构处有无预紧力两种情况时在均布载荷作用下梁的非线性幅频响应。同时,利用改进的振型转化法及连续振型法对系统进行建模,采用伽辽金近似得到系统的非线性受迫振动方程;针对实际算例,用龙格-库塔法得到了其数值解,讨论了此算例梁的频率漂移结果,从而得到了对研究航天器地面振动试验中的频率漂移现象有价值的结论。     

Peristaltic transport of a viscoelastic fluid in a channel

This paper is devoted to the study of the peristaltic transport of viscoelastic non-Newtonian fluids with fractional Maxwell model in a channel. Approximate analytical solutions have been constructed using Adomian decomposition method under the assumption of long wave boundary layer type approximation and low Reynolds number. The effects of relaxation time, fractional parameters and amplitude on the pressure difference and friction force along one wavelength are received and analyzed. The study is limited to one way coupling model with forward effect of the fluid on the peristaltic wall. It is evident from the result that pressure diminishes with increase in relaxation time and the effects of both fractional parameters on pressure are opposite to each other. The influences of these parameters on friction force are opposite to that of pressure.     

Application of a magnetohydrodynamic element in the control loop of a rotating spacecraft with a spike antenna

The problem of stabilization of a rotating spacecraft with a flexible spike antenna located along the axis of spacecraft rotation is considered. A magnetohydrodynamic element is used as a final-control element in the control loop of spacecraft attitude, and the solar direction sensor serves as a measuring device. At the first stage of investigation, the problem of stability is considered for stationary and non-stationary modes of rotation of the spacecraft with a flexible antenna and with a cavity partially filled with a low-viscosity liquid.     

航天器两自由度扫描镜图像运动补偿技术研究

研究航天器的两自由度扫描镜图像运动补偿问题。在姿态估计信息的基础上,给出了一种运动补偿算法。算法中不仅补偿了姿态估计信息,还同时考虑了姿态信息中的长周期系统误差。利用扫描镜在特定工作模式下相对惯性空间的准确定向能力和系统误差的长周期特性,给出了一种系统误差的估计和补偿算法,每隔一定的时间段对系统误差估计值进行更新并加以补偿,进一步提高了扫描精度。基于一颗地球静止轨道卫星的数值仿真结果验证了补偿算法的有效性。     

Spreading and break-up of a drop in a gas stream

Based on the expansion of unknown functions in a series of a small parameter, an analytical method is developed for calculating the time-dependent motion and a spreading (up to the break-up) of a plane and axisymmetric drop in a gas stream. It is shown that the zero-order terms of expansion define a clear retardation of a drop as a solid sphere. The next terms of the series characterize deformation and spreading of the drop.Based on the solution of the boundary-value problem of drop spreading the infinite system of linear differential equations with constant coefficients is obtained. It is established that without viscosity the system contains a finite number of equations and permits an exact solution. The spreading of an ideal liquid drop with the surface tension force taken into account was investigated in detail. In the case of a water drop placed in nitrogen a comparison was made between the calculated results on drop shapes and experimental data obtained at different moments of time. The theory agrees with the experiment both qualitatively and quantitatively.     

Mass determination of a small body in solar system by using a test-mass during a fly-by

The mass estimation of small bodies in the solar system—such as comets or minor planets—with an accuracy sufficient to get scientific information is difficult. The ground-based range-rate measurements are not practicable for bodies smaller than 100 km diameter.A proof mass, ejected from the spacecraft before the flyby and whose relative trajectory is determined with onboard measurements can give very good results even for small bodies. This paper presents the expected accuracy of mass determination depending on ballistic conditions (relative velocity and closest approach), type and accuracy of measurements (range, optical).     

Station keeping of a solar sail around a Halo orbit

Solar sails are a concept of spacecraft propulsion that takes advantage of solar radiation pressure to propel a spacecraft. Although the thrust provided by a solar sail is small it is constant and unlimited. This offers the chance to deal with novel mission concept. In this work we want to discuss the controllability of a spacecraft around a Halo orbit by means of a solar sail. We will describe the natural dynamics for a solar sail around a Halo orbit. By natural dynamics we mean the behaviour of the trajectory of a solar sail when no control on the sail orientation is applied. We will then discuss how a sequence of changes on the sail orientation will affects the sail's trajectory, and we will use this information to derive efficient station keeping strategies. Finally we will check the robustness of these strategies including different sources of errors in our simulations.     

Stabilization of a Reentry Vehicle by a Partial Spin-up during Uncontrolled Descent

Stabilization of a reentry vehicle (RV) by a partial spin-up of it is considered for the case of uncontrolled descent into the atmosphere. In this case, the vehicle is a composite construction consisting of two rigid bodies, a return capsule and a stabilizing block, which is put in rotation. A model is developed for the spatial motion of the reentry vehicle considered as a system of coaxial rigid bodies rotating about a common axis of symmetry. The free motion is studied, and the stability of steady-state regimes is analyzed. The spatial motion of the system is considered for the case of a small asymmetry due to displacement of the axes of dynamic symmetry of the bodies with respect to the spin axis, and approximate solutions for the motion parameters of the free system are found.     

发散波束在媒质界面上的Goos-H(a)nchen位移与焦移

在全反射中研究了发散波束在两种不同媒质界面上Goos-H(a)nchen位移与焦移.首先,通过建立发散光束全反射简单光线模型来显示焦移的形成.然后,从波动光学出发,利用Fourier光学中的角谱法推导出Gauss发散波束入射下Goos-H(a)nchen位移和焦移的近似关系式.结果表明,由Carniglia 和 Brownstein 针对于均匀波束提出的Goos-H(a)nchen位移和焦移的微分关系式同样也适用于Gauss发散波束入射的情况.最后,通过数值模拟总结出了焦移的一些不同于Goos-H(a)nchen位移的特殊性质.这些特殊性质的发现为改善现有实验和工程精度提供了新路径.     

Guidance of a spacecraft with low lift-to-drag ratio to a landing point

The problem of terminal control over a deorbiting spacecraft at the stage of its flight after leaving plasma (altitude of ∼40 km) is considered, the aim being to guide it to a preset landing point. The algorithm is based on a modification of the well-known method of proportional navigation, when a fixed point is the target. It is suggested to use satellite navigation systems (of the GLONASS or GPS types) and/or radio beacons, which should allow one to determine the spacecraft trajectory parameters with high precision. Single-channel control is performed by changing the roll angle according to current parameters of the trajectory, which ensures adaptability of the method. Examples of three-dimensional trajectories of flight are presented for a manned spacecraft with low lift-to-drag ratio (∼0.5), currently under design in Russia. The results of statistical modeling taking into account initial deviations of the trajectory parameters and wind disturbances are presented. A method of statistical choice of a reference trajectory for the guidance stage is suggested. A theoretical possibility of using the algorithm of spacecraft guidance (in case of in-light accident with a carrier launcher) to preset regions in the vicinity of launching route is demonstrated. A qualitative analysis of proportional navigation with a fixed target is presented.     

Orbital stability of planar oscillations of a satellite in a circular orbit

We consider the attitude motion of a satellite with a circular orbit in a central Newtonian gravitational field. The satellite is a solid body whose mass geometry is that of a plate. A nonlinear analysis is made of orbital stability of planar oscillations of the satellite at which its middle or major axis of inertia is perpendicular to the orbit plane. At small amplitudes of oscillations the analysis of stability was made analytically, while for arbitrary amplitudes the numerical analysis was performed.     

Optimization Problem in Control over a Programmed Turn of a Spacecraft

The problem of spacecraft reorientation from its initial angular position into a desired final position within a given time interval with a minimum value of the angular moment is considered and solved analytically in this work. It is shown that the control over the spacecraft reorientation, optimal in this sense, might be defined in the class of a regular precession performed by the spacecraft. The moment of the start of deceleration is determined from the principles of the terminal control by using real kinematic parameters of apparatus motion, which increases significantly the accuracy of reorientation. The results of mathematical modeling are presented, showing a high efficiency of the proposed way of reorientation.     

缝隙平面天线与TEM喇叭组合的超宽带馈源

根据紧缩场天线测试系统对馈源的要求,选择缝隙平面馈电结构与TEM喇叭组合的新颖技术实现馈源的超宽带、电小尺寸、天线的E面和H面方向图3dB波束宽度等化,从而使馈源达到高性能、体积小、重量轻和容易安装等目的,满足低频紧缩场天线测试系统的要求。     

某型卫星有效载荷支架振动抑制

某型号卫星的有效载荷支架结构在验收级振动试验时振动超标。在对结构不做大的修改的前提下，采用约束阻尼层用对原结构进行处理。对不同的约束阻尼层方案采用有限元方法进行计算，综合考虑各种影响因素，如阻尼比和附加质量等，得到合理的约束阻尼减振方案，并在结构星上进行试验，确定最终实施方案。实施方案后，正样星在0．1g振动条件下，最大振动幅值下降了22．3％，保证了卫星的顺利发射。该卫星已经成功发射，并且在轨运行正常。该问题的成功解决和解决问题的方法与过程为今后解决类似问题提供了经验。     

通过纯软件的方法测试数字处理器的故障敏感性

对于工作在高辐射太空中的飞行器而言，它不可避免会受到单粒子效应的影响。因此，如何预测飞行器中单粒子效应敏感区域以便加强保护措施是一件很重要的工作。但事实上，要预测单粒子效应对飞行器的影响并不容易。本文给出了一种通过纯软件来评测飞行器系统对单粒子效应的敏感程度的方法——软件故障注入法——这也是评测微电子电路可靠性极具前景的方法。该方法采用高效的汇编语言在汇编级实现，对目标系统不会造成损伤，并且使用方便。试验的结果表明，目标处理器对于单粒子翻转的敏感性大约为1．38％到2．35％，且寄存器的敏感性要高于内存区。     

落压式供应发生器试验系统动态仿真

某上面级液氧/煤油补燃发动机的发生器拟采用落压式挤压供应试验系统方案,为了验证其单独热试方案的可行性,建立发生器热试系统的动态数学模型,并进行数值仿真计算,确认了试验系统方案的可行性,同时提出了分级起动方式并确定了起动工况。试验取得了成功,试验结果与仿真吻合,验证了仿真计算的正确性。     

Selecting a reference frame

Reference frames are representations that parse space. In the case of spatial terms, reference frames mediate the mapping of linguistic expressions onto spatial configurations of objects. In the sentence ``The fly is above the cat,' ``above' is defined with respect to a reference frame that is imposed on the cat. Different types of reference frames can be used to define spatial terms, each based on a different source of information. For example, gravity, the orientation of objects in the scene or the orientation of the viewer can all be used to set the orientation of a reference frame. When these reference frames disagree (because the viewer is reclining or because the objects in the scene are overturned), there are competing definitions for the spatial term, resulting in the need for reference frame selection. The purpose of this paper is to review a line of research that examines reference frame selection in the context of spatial language. This work shows that all reference frames are initially active and assign a direction to a spatial term. Moreover, this activation is automatic, and is followed by the selection of a single reference frame, with selection accompanied by inhibition of the non-selected frames. Parallels between reference frame selection in language and in perception and attention are discussed.