The White Sands Range and Range-Rate System

This paper discusses the concept, design, and design verification of the White Sands Range and Range-Rate System. Development of the system has been completed only through the design phase. The system is designed to meet requirements for high-accuracy midcourse tracking under severe target dynamics at the White Sands Missile Range. It is a multistatic Doppler and range tracker which operates at X band and incorporates transmitter, transponder, receiver, and baseline subsystems. The transmitter includes specially designed digital circuitry to synthesize test signals for target simulation during checkout of the system. The transponder signal is processed by a receiver which has been established theoretically to be the optimum realizable processor of continuous tracking data. The receiver incorporates specially designed carrier acquisition circuitry and digital VCO, and directly provides digital Doppler and tone phase data to facilitate real-time processing. The system utilizes data from other tracking systems at the Range for spatial acquisition, for aiding carrier acquisition in the receiver, and for resolving range ambiguities.     

An overview by pioneers observations of the distant geomagnetic tail

Pioneer 7 and Pioneer 8 spacecraft provided the only direct observations of the geomagnetic tail at geocentric distances as large as 1000R _e and 500R _e respectively. The presence of a low density plasma flow in the region of expected tail and the intermittent and short duration character of the tail encounters suggested in the past a distant tail structure remarkably different from its near-earth and cislunar shape. However the recent discovery of the plasma mantle allows to interpret the Pioneer observations in terms of a distant tail that possibly is still preserving most of its near-earth characteristics. In particular, the region of tail encounters and the magnitude and direction of the observed magnetic field might be consistent with a cylindrical tail with a modestly increased cross-section. Neutral sheet observations also appear to be consistent with the most recent bidimensional tail models. Finally, as in the cislunar region, the double peaked proton energy spectra can be interpreted in terms of a partial intermingling of plasma sheet and plasma mantle populations.Also at Laboratorio Plasma nello Spazio, CNR, Frascati.     

Optimum Realizable Continuous Range Estimation

The ability to detect the presence or absence of a target is no longer the fundamental design criterion when the vehicle to be tracked is cooperative. In spacecraft tracking or navigation systems, for example, emphasis is placed on post-acquisition performance. Therefore, classical radar theory and design techniques are not specifically applicable. On the other hand, there are optimization techniques for extracting the tracking data from noise that are more to the point. In particular, optimum demodulation theory is directed specifically to the problem of continuously extracting data from a nonlinear modulation process. In this paper, the tracking properties of a multitone PM ranging signal are reviewed and are shown to be nearly optimum for cooperative vehicles. An optimum, but nonrealizable, maximum a posteriori (MAP) continuous estimator of range is derived for this signal. The linearized model of this receiver is the optimum nonrealizable Wiener filter for the data. Interpretation of this optimum nonrealizable estimator leads to a receiver design that is both practical and intuitively satisfying. With the aid of post-detection processing in the Wiener-Hopf sense, almost optimum performance is obtained from the resulting receiver, above threshold.     

Event-triggered adaptive control for attitude tracking of spacecraft

Plug-and-play technology is an important direction for future development of spacecraft and how to design controllers with less communication burden and satisfactory performance is of great importance for plug-and-play spacecraft. Considering attitude tracking of such spacecraft with unknown inertial parameters and unknown disturbances, an event-triggered adaptive backstepping controller is designed in this paper. Particularly, a switching threshold strategy is employed to design the event-triggering mechanism. By introducing a new linear time-varying model, a smooth function, an integrable auxiliary signal and a bound estimation approach, the impacts of the network-induced error and the disturbances are effectively compensated for and Zeno phenomenon is successfully avoided. It is shown that all signals of the closed-loop system are globally uniformly bounded and both the attitude tracking error and the angular velocity tracking error converge to zero. Compared with conventional control schemes, the proposed scheme significantly reduces the communication burden while providing stable and accurate response for attitude maneuvers. Simulation results are presented to illustrate the effectiveness of the proposed scheme.     

Conical Scanning System for Pioneer Jupiter Spacecraft

The concept, operation, and predicted performance of an RF tracking control system used to point the Pioneer F/G spacecraft at the Earth is described. This system employs a modified conical scanning technique called Conscan. The signal processor, the most interesting unit of the system, is described in detail to show that it approximates a maximum likelihood estimator. The dynamic behavior of the spacecraft and the stability analysis of the system are presented, demonstrating that the system performance is basically determined by the open-loop phase and amplitude errors introduced by the antenna, receiver, and signal processor. A detailed error budget shows that the phase and amplitude errors are small. Finally, closed-loop simulation and test data are presented to verify the error budget.     

非合作航天器姿态接管无辨识预设性能控制

在对非合作航天器进行姿态接管控制时,可能面对目标航天器参数未知、构型改变引起的不确定性及目标施加的非合作控制输入等挑战。针对上述问题提出了一种基于预设性能控制理论的非合作航天器姿态接管控制方法。首先,建立了姿态跟踪运动的非奇异拉格朗日型模型;然后,利用跟踪微分器构造不包含角速度信息的广义状态量,设计无需参数辨识的非奇异预设性能控制器,并证明了系统状态变量的有界性和控制系统在预设的性能指标以内。最后,通过数值仿真验证了所提出方法的有效性及其对时变参数不确定性和非合作控制输入的鲁棒性。     

航天器多普勒测速平均误差的分析与修正

对航天器多普勒测速平均误差进行了分析,详细推导了圆轨道和椭圆轨道时该误差的计算公式,计算了不同采样周期和轨道高度时的误差大小。经过分析指出,该项误差对于高轨航天器影响较小,对于低轨航天器可以通过缩短采样周期或利用3个点或多个点的连续测量数据进行修正。     

Extended Area Range Instrumentation System Utilizing DME Links

Updated and expanded range instrumentation installations require a system capable of actually tracking and controlling large numbers of vehicles over expanded areas. A range instrumentation system is discussed based on distance measurement equipment (DME) coupled with high performance data links which satisfies these requirements. Previously developed DME systems utilized a single frequency data link, required a low sample rate, and accomodated only a few vehicles. The DME range instrumentation system described will handle a large number of test vehicles and accomodate high data rates without performance degradation. This is accomplished by incorporating surface acoustic wave (SAW) devices and microprocessors with previous developed technology. A system performance analysis for various configurations of the range instrumentations system design is also presented.     

基于新型终端滑模的航天器执行器故障容错姿态控制

针对受干扰的刚体航天器冗余执行器存在故障与控制受限的姿态跟踪控制问题,提出一类基于新型指数形式的非奇异快速滑模面（ENFTSM）与趋近律的姿态容错控制器设计方法。当部分推力器发生故障时,假设剩余推力器具有输出饱和特性且能提供足够推力保证航天器执行任务,相比一般终端滑模控制器,本文设计的控制器不仅能使系统状态以更快的速度到达平衡点,且不需要在线对执行器故障信息进行检测和分离。基于Lyapunov方法证明本文设计的控制器能保证闭环系统稳定,且能有效地抑制外部干扰、控制受限和执行器故障等约束。最后对提出的控制算法进行了数值仿真,其结果表明了该控制器的有效性。     

航天器自适应快速非奇异终端滑模容错控制

针对存在外部干扰、转动惯量矩阵不确定、控制器饱和以及执行器故障的航天器姿态跟踪控制问题,提出了基于自适应快速非奇异终端滑模的有限时间收敛控制方案。通过引入能够避免奇异点的具有有限时间收敛特性的快速非奇异终端滑模面,设计了满足多约束的有限时间姿态跟踪容错控制器,并利用参数自适应方法使控制器设计不依赖于系统惯量信息和外部干扰的上界。此外,所设计的控制器显式考虑了执行器输出力矩的饱和幅值特性,使航天器在饱和幅值的限制下完成姿态跟踪控制任务,并且无须进行在线故障估计。Lyapunov稳定性分析表明：在外部干扰、转动惯量矩阵不确定、控制器饱和以及执行器故障等约束条件下,所设计的控制器能够保证闭环系统的快速收敛性,而且对控制器饱和与执行器故障具有良好的容错性能。数值仿真校验了该控制器在姿态跟踪控制中的优良性能。     

Flexible loop filter design for spacecraft phase-locked receivers

A flexible loop filter design for spacecraft phase-locked receivers is proposed. The loop filter is implemented as digital hardware with coefficients that are set by registers. Either a perfect or an imperfect integrating loop filter can be effected. This flexibility is important since not one type of loop filter is preferred for all circumstances. An imperfect integrator is preferred when, as is often the case for spacecraft receivers, it is important to minimize the best-lock frequency drift of an idling loop. A perfect integrator is preferred when the tracking performance of the loop is the most important consideration     

基于新型终端滑模的航天器执行器故障容错姿态控制简

 针对受干扰的刚体航天器冗余执行器存在故障与控制受限的姿态跟踪控制问题,提出一类基于新型指数形式的非奇异快速滑模面（ENFTSM）与趋近律的姿态容错控制器设计方法。当部分推力器发生故障时,假设剩余推力器具有输出饱和特性且能提供足够推力保证航天器执行任务,相比一般终端滑模控制器,本文设计的控制器不仅能使系统状态以更快的速度到达平衡点,且不需要在线对执行器故障信息进行检测和分离。基于Lyapunov方法证明本文设计的控制器能保证闭环系统稳定,且能有效地抑制外部干扰、控制受限和执行器故障等约束。最后对提出的控制算法进行了数值仿真,其结果表明了该控制器的有效性。     

连续地月转移系统动力学研究与能量分析

为了研究新型连续地月转移系统的动力学及能量需求,采用Lagrange方法,在系绳为刚性杆假设的前提下,同时忽略第三体引力、地球扁率和系绳轴向变形等扰动因素的影响,建立了驱动型动量交换绳系卫星(MMET)系统的三维刚性动力学模型。对所建立的动力学模型进行了数值仿真及对比分析,仿真结果验证了所建模型的正确性。研究表明,外力矩对系统轨道运动参数影响甚小,对姿态运动参数影响明显。采用MMET方式进行载荷转移,推导出了实现载荷地月轨道转移所需的入口速度条件以及时间周期条件,并求解出了载荷在2次任务之间的时间间隔。给定初始条件下,当MMET系统以0.231 6 rad/s的旋转角速度绕其质心旋转1 448.5圈,其绕地心刚好运行5圈时,载荷可顺利进入地月转移轨道。最后,对连续地月转移系统实现载荷的地月转移进行了能量对比分析,结果表明,相同条件下,MMET载荷转移方式相比于传统脉冲变轨方式在载荷转移过程中消耗更少的能量。     

The Orbiting Geophysical Observatories

The Orbiting Geophysical Observatories and the supporting ground checkout equipment, data acquisition and tracking stations and data processing equipment are designed to conduct large numbers of diverse experiments in space. Measurements will be made within the earth's atmosphere, ionosphere, exosphere, magnetosphere, and in cislunar space to obtain a better understanding of earth-sun relationships and of the earth as a planet. Configured to meet scientific requirements, the observatories include six booms to support detectors away from disturbances generated in the main body. Five degrees of freedom allow the orientation of experiments relative to three references — the earth, the sun, and the orbital plane. Power, thermal control, and data handling subsystems provide for the proper operation of the experiments and telemetry of the data. Ground stations receive these data, which are then processed into a form suitable for use by the experimenters. The systems have been designed to make available a standard spacecraft and support equipment which can be used repeatedly to carry large numbers of easily integrated experiments in a wide variety of orbits.     

小推力航天器的地月低能转移轨道

 在限制性四体模型下研究基于小推力方式的地月低能转移问题,通过借助于平动点轨道的相空间结构来揭示小推力转移的机理。重点研究了小推力转移自由飞行段的构造：经由LL₁点穿越获得最小能量的低能转移;而经由LL₁点Halo轨道穿越,得到(M,N)圈穿越轨道;由于Halo轨道相对于平动点增加了一维度的选择,根据(2,2)圈穿越轨道构造该转移的自由飞行段。在地球势阱逃逸和月球势阱捕获段,分别设计了合适的小推力的控制律及发动机开/关机时间,成功实施近地球段的小推力加速和近月球段的减速。尽管未对所得到的结果进行优化,所得转移轨道的燃料消耗也与类似边界条件的SMART-1轨道基本一致。     

Rejection of Multipath Interference in Satellite Communications by Use of Narrow-Band Filters

Earth-reflected multipath interference can be serious for communication between near-earth spacecraft and stationary satellites. It is shown that both the depth and rate of fading are reduced by using narrow-band filters. Curves demonstrate the saving in fading margin; this saving may be crucial in an emergency.     

Velocity changes of the Giotto spacecraft induced during the flybys of the comets P/Halley and P/Grigg-Skjellerup

The Giotto Radio-Science Experiment (GRE) was designed to measure the reaction of the spacecraft to its close encounters with the comets P/Halley and P/Grigg-Skjellerup. Radio frequency and signal level data of the downlink carrier signals at X- and S-band, recorded at many ground-based tracking stations, were used for the previous analysis. These signals were transmitted in “one-way” mode (Giotto - Earth) during a few hours about closest approach and in “two-way” mode (Earth - Giotto - Earth) during the adjacent pre-encounter and post-encounter tracking intervals. Unexpectedly large differences for the comet-induced Doppler shift residual of the Giotto signal were implied by the one-way versus the two-way data, a discrepancy which was attributed to instabilities of the on-board oscillator during the encounter. The analysis to date assumed that the two-way Doppler shift residual is exactly twice the one-way residual. As shown in this note, this is not generally the case. The spacecraft's change in velocity, which is measured in a rotating (non-inertial) system, must first be determined in the non-rotating frame by applying the appropriate coordinate transformation. The GRE results should be reinvestigated to account for this previously unrecognized effect.     

Tracking and data acquisition for space exploration

The tracking and data acquisition systems provide the key link between the remote spacecraft and the scientific experimenter on the ground. The operation of the space experiment takes place through the links of command, telemetry and tracking. The evolution from the early very simple spacecraft missions toward more complex and sophisticated missions has been paralleled by a similar evolution in the tracking and data acquisition systems. The early Minitrack interferometer tracking system still carries the major tracking workload for space missions; however greater tracking accuracy requirements for more recent missions, such as the Orbiting Geophysical Observatory and the Apollo mission, have brought about the development of unified tracking and data acquisition systems which utilize hybrid pseudo-random code/sidetone ranging techniques. The data acquisition has evolved from analog telemetry systems to the present day heavy use of PCM digital telemetry. Likewise the command systems have evolved from early simple on/off command systems into PCM digital command data systems. The trend is toward greater real time control of more complex functions on board the spacecraft. Newer spacecraft are incorporating computer-type systems in the spacecraft which require programming and memory load through the ground command link. The most attractive concept for the next generation network for tracking and data acquisition is a network consisting of synchronous-orbit Tracking and Data Relay Satellites for covering launches and low-orbit earth satellites plus a few selected ground stations for supporting spacecraft in high earth orbit and lunar orbit.     

基于“虚拟范围”的多机器人围捕算法

 讨论了基于SQL Server数据库的栅格地图建立方法。介绍了一种建立在势场法和栅格地图上的室外多机器人路径规划方法，分析了在已知地图中应用势场法进行路径规划时的路径死点和规划失败问题，并给出了解决方法。以势场栅格法为基础探讨了多机器人协作围捕动态目标的策略。在围捕算法中，根据室外机器人工作环境的特点，提出了“虚拟范围”的概念，以减少动态规划次数，提高围捕速度。介绍了机器人以“虚拟范围”为基准，在各种状态之间的转换机制。利用基于无线局域网的室外多机器人系统进行了试验，试验表明引入“虚拟范围”之后能有效缩短围捕时间，并且存在最短时“虚拟范围”。
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