Real time estimator for control of an orbiting single tether system

A real-time estimator is developed for the control of the Tether Dynamics Explorer (TDE) system. TDE is being used in a series of tethered satellite flight experiments whose purpose is to validate existing system models and test proposed control laws. Each experiment consists of an orbiting Delta II second stage which deploys toward the Earth a small box-shaped passive endbody at the end of a flexible tether. A discrete extended Kalman filter (DEKF) is presented which can operate in real time and in conjunction with control laws. This filter estimates the in-plane and out-of-plane tether libration angles and their rates from a proposed three-axis tether tension measurement device in the Delta second stage. The simulation results indicate that the DEKF can estimate the libration angle and their rates from a three-axis tension and length measurement with an acceptable error. The relatively simple computations required make this algorithm particularly well suited for real-time operation.<>     

TDE—85/芳香族胺固化体系动力学研究

测试了TDE—85/芳香族胺体系在不同升温速率下的DTA曲线,通过Ozawa方程、Kissinger方程计算各体系的活化能,利用Crane方程计算各体系的反应级数。结果表明,DTA曲线均呈单峰,两种计算活化能的方法近似,TDE—85中两种环氧基反应活性近似,各体系反应级数均接近于1级反应。     

硼酸铝晶须增强TDE-85型环氧树脂复合材料研究

以硼酸铝晶须为增强剂，以4，5-环氧环己烷-l，2-二甲酸二缩水甘油酯(TDE-85)／甲基纳狄克酸酐(MNA)作为基体，采用浇注成型工艺制备晶须增强环氧树脂复合材料。考察了晶须尺寸、表面处理方法、含量对树脂体系力学性能和热性能的影响。结果表明，用偶联剂KH550处理晶须时，所用溶剂pH值会影响晶须的处理效果，酸化溶剂的效果更好；晶须长径比比较大、尺寸分布均匀的晶须其增强效果更好；晶须可明显改善体系的力学性能和耐热性，其中弯曲强度随晶须含量的增加而增大，当晶须含量超过一定量时，弯曲强度反而呈现下降趋势，晶须对体系冲击强度的影响较小，体系的热变形温度随晶须含量的增加而增大，在晶须添加量为15％(质量分数)左右时，所得体系的综合性能较好。     

碳纤维单轴向缝编织物及其复合材料性能影响研究

以碳纤维单轴向缝编织物为研究对象,开展了树脂体系及其复合工艺、织物结构参数和碳纤维种类对碳纤维单轴向缝编织物使用工艺性及其复合材料主要力学性能的影响研究。结果表明:经向碳纤维和衬纬材料的种类及其面密度等结构参数对织物弯曲硬挺度和织物单向渗透率的影响规律基本相似;无论是碳纤维缝编织物单向渗透率还是复合材料的主要力学强度,真空吸附工艺中,基于TDE-85环氧树脂的自制6#环氧树脂体系均明显优于市售用基于双酚A环氧树脂的环氧树脂体系;采用610A树脂预浸料工艺、或经向碳纤维的适当展纱、或干喷湿法纺丝技术制备的碳纤维,均有利于进一步提高碳纤维单轴向缝编织物复合材料的主要力学性能。这为碳纤维缝编织物结构设计、主要原材料选择、制备工艺、配套树脂体系及其复合工艺等选择优化提供一些参考,为碳纤维缝编织物、尤其是为国产碳纤维缝编织物的制备和推广应用奠定了良好基础。     

On the relation between the mass loss rate and the stellar parameters of OB-type stars

We discuss mass loss relations for OB-type stars as a function of luminosity, effective temperature, and mass. We conclude that a simple first order linear regression relation is as good as any other more sophisticated relation, with the advantage that the simple form consumes much less computer time when used in evolutionary codes.     

Estimation near "Zero Information" points: angle-of-arrival near the endfire

We examine large-sample properties of the maximum- likelihood estimator (MLE) in the vicinity of points where the Fisher information measure (FIM) equals zero. Under mild regularity conditions the MLE is asymptotically efficient and therefore lower bounded by the Cramer-Rao lower bound (CRLB) [5], which diverges for such points. When a linear sensor array is used for angle-of-arrival (AOA) estimation, the CRLB diverges as the AOA approaches pi/2. We provide new results characterizing the MLE performance in the AOA problem.     

Evaluating sensor technology for UAS collision avoidance

The problem of "sense-and-avoid" for Unmanned Aircraft Systems (UAS) is genuinely multi-dimensional: there is a wide range of UAS sizes, speeds, and maneuverability, as well as missions for which these UAS will be used. There are also a variety of sensors that might be used for sense-and-avoid, which have widely varying capabilities to measure distance or angle to an obstacle, as well as closing rate, and time to collision. Most sensors are not able to provide all required information about the geometry of an encounter; therefore, using a combination of sensors offers one possible solution. We are investigating the concept that there may be a variety of possible sensor solutions for each distinct UAS capability or mission. By studying the breadth of UAS types and missions, and selectively testing certain sensors in the field, we are evaluating the limits to the capabilities of sensors and sensor combinations. This report is on the progress of this multi-dimensional evaluation. We have scoped the dimensions for evaluating UAS capabilities and the capabilities of sensors. We are experimentally evaluating sensor parameters on a variety of aircraft to validate the specified capabilities. This reports on our methodology for field evaluation of sensor technology and the lessons learned on evaluation platforms and capabilities.     

Pickup Ion Acceleration at the Termination Shock and in the Heliosheath

We discuss pickup ion acceleration and transport near the solar wind termination shock from the perspective of their spectral, spatial, and pitch-angle distributions. Our study is performed in the framework of a recently developed anisotropic transport model based on a Legendre polynomial expansion technique. Voyager 1 LECP angular distributions of 1 MeV protons, represented in the form of an expansion in spherical harmonics in the frame aligned with the measured interplanetary magnetic field, are used as benchmarks for our theory. We find the observed distributions consistent with our model predictions for particle acceleration and reflection at a highly oblique shock wave. It is shown that first-order (field aligned) anisotropy is a measure of shock obliquity while the second-order (transverse) anisotropy reflects the energy dependence of the particle scattering mean free path. We also discuss the role of enhanced scattering and momentum diffusion on the spectral properties of energetic charged particles.     

Reduced spatio-temporal complexity MMPP and image-based tracking filters for maneuvering targets

We present reduced-complexity nonlinear filtering algorithms for image-based tracking of maneuvering targets. In image-based target tracking, the mode of the target is observed as a Markov modulated Poisson process (MMPP) and the aim is to compute optimal estimates of the target's state. We present a reduced complexity algorithm in two steps. First, a gauge transformation is used to reexpress the filtering equations in a form that is computationally more efficient for time discretization than naive discretization of the filtering equations. Second, a spatial aggregation algorithm with guaranteed performance bounds is presented for the time-discretized filters. A numerical example illustrating the performance of the resulting reduced-complexity filtering algorithms for a switching turn-rate model is presented.     

Evaluation of built-in test

Built-in test (BIT) provides fault finding as a means to aid in system assembly, test, and maintenance. An investigation to evaluate BIT of a particular electronics board used in the in-flight entertainment system for Boeing 777s is described. We found BIT proved useful when failure occurrences were uniquely associated with the operating environment, situations which can result in no-fault found, or could-not duplicate (CND) failures upon test. We also observed cases where the BIT failed to observe failures, and in some cases pointed to the wrong cause of failure. These and other advantages and disadvantages of BIT implementation are discussed     

Choice of flight conditions and modes of engine operation for its diagnostics

We consider a method for diagnostics of the engine flow passage technical status of a maneuverable aircraft operating in a wide range of altitudes and speeds; the behavior of measured parameter deviations from throttle characteristics and calculated characteristics of the flow passage units from their initial values is used for diagnostics. We present the methods for determining these deviations as well as flight conditions and engine operation modes at which diagnostics is made possible.     

基于SNA的航空发动机空中停车文献分析

由于发动机故障引起的空中停车存在高危险性和不确定性,必须做好防范和处置。在 CNKI 数据库中以“空中停车”关键词检索相关研究文献,应用 SATI3.2 软件对检索文献数据进行数据预处理,获取高频关 键词并构建共词矩阵;应用 Ucinet6.0 软件对关键词进行社会网络分析和聚类分析。结果表明:航空发动机空中停车研究领域热点集中于管理、维修、人员及企业运营等方面;民用航空与军用航空在该领域的研究重点存在差异;非常规类飞机的空中停车受到关注,无人机空中停车研究将成为该领域的热点问题;军用飞机空中停车研究成果相比民用飞机存在一定差距,随着军用飞机适航工作的开展和推进,军用飞机空中停车研究将在该领域占据重要地位。     

The Plasma Environment of Comet 67P/Churyumov-Gerasimenko Throughout the Rosetta Main Mission

The plasma environment of comet 67P/Churyumov-Gerasimenko, the Rosetta mission target comet, is explored over a range of heliocentric distances throughout the mission: 3.25 AU (Rosetta instruments on), 2.7 AU (Lander down), 2.0 AU, and 1.3 AU (perihelion). Because of the large range of gas production rates, we have used both a fluid-based magnetohydrodynamic (MHD) model as well as a semi-kinetic hybrid particle model to study the plasma distribution. We describe the variation in plasma environs over the mission as well as the differences between the two modeling approaches under different conditions. In addition, we present results from a field aligned, two-stream transport electron model of the suprathermal electron flux when the comet is near perihelion.     

Precision large scale air traffic surveillance using IMM/assignmentestimators

We present the development and implementation of a multisensor-multitarget tracking algorithm for large scale air traffic surveillance based on interacting multiple model (IMM) state estimation combined with a 2-dimensional assignment for data association. The algorithm can be used to track a large number of targets from measurements obtained with a large number of radars. The use of the algorithm is illustrated on measurements obtained from 5 FAA radars, which are asynchronous, heterogeneous, and geographically distributed over a large area. Both secondary radar data (beacon returns from cooperative targets) as well as primary radar data (skin returns from noncooperative targets) are used. The target IDs from the beacon returns are not used in the data association. The surveillance region includes about 800 targets that exhibit different types of motion. The performance of an IMM estimator with linear motion models is compared with that of the Kalman filter (KF). A number of performance measures that can be used on real data without knowledge of the ground truth are presented for this purpose. It is shown that the IMM estimator performs better than the KF. The advantage of fusing multisensor data is quantified. It is also shown that the computational requirements in the multisensor case are lower than in single sensor case, Finally, an IMM estimator with a nonlinear motion model (coordinated turn) is shown to further improve the performance during the maneuvering periods over the IMM with linear models     

时间依赖边界条件在亚声速自由射流数值模拟中的应用

对亚声速自由射流进行数值模拟时，无法预先给定远场边界和无反射入流边界上的速度值。以往采用的黎曼不变量在自由边界上给定无反射条件的处理方法，只给出了这些边界法线方向上的一维特征关系。时间依赖边界条件是一种高精度的边界处理方法，可以很方便地处理计算中遇到的各种边界，广泛地应用于DNS中。我们将这种边界条件用于定常流动的计算中，计算了出口马赫数为0．4和0．7的轴对称自由射流，获得了与实验结果吻合的数值模拟结果。     

Optimal sensor selection strategy for discrete-time stateestimators

A novel sensor selection strategy is introduced, which can be implemented on-line in time-varying discrete-time system. We consider a case in which several measurement subsystem are available, each of which may be used to drive a state estimation algorithm. However, due to practical implementation constraints (such as the ability of the on-board computer to process the acquired data), only one of these subsystems can actually by utilized at a measurement update. An algorithm is needed, by which the optimal measurement subsystem to be used is selected at each sensor selection epoch. The approach described is based on using the square root V-Lambda information filter as the underlying state estimation algorithm. This algorithm continuously provides its user with the spectral factors of the estimation error covariance matrix, which are used in this work as the basis for an on-line decision procedure by which the optimal measurement strategy is derived. At each sensor selection epoch, a measurement subsystem is selected, which contributes the largest amount of information along the principal state space direction associated with the largest current estimation error. A numerical example is presented, which demonstrates the performance of the new algorithm. The state estimation problem is solved for a third-order time-varying system equipped with three measurement subsystem, only one of which can be used at a measurement update. It is shown that the optimal measurement strategy algorithm enhances the estimator by substantially reducing the maximal estimation error     

Aircraft maintenance jacking problem via optimization

We address the problem of assigning forces to jacking positions in order to weaken stress at points where an aircraft maintenance operation has to be performed. We introduce a mixed-integer linear programming model and report encouraging computational experiments on historical data. Our methodology is currently under the process of industrial implementation at Airbus, where it will be used as a maintenance decision-analysis tool.     

On the Effective Single Trial Probability of Success

Define the cumulative probability Pn of occurence of some event as the probability that it occurs at least once in n trials. If the single trial probabilities are not fixed, but are drawn from a distribution of their own, or are dependent on some other nonfixed variable, then it would be convenient to have an ?effective single trial probability (esp)? for use in the simple Bernoulli model which would give the same cumulative probability of occurence as actually observed. We show here that the esp can be interpreted as a kind of average, and that its value is given by 1 minus the geometric mean of 1-d(p), where d(p) is the probability density function of the single trial probabilities, the p's. We further define this geometric mean for both discrete and continuous distributions and evaluate the esp for several cases. These results are compared with earlier ones which suggest that the esp is given by the (arithmetic) average or expectation of the single trial probabilities, and we determine under what conditions this simpler result can be used.     

Correlation of Binarized Images

Correlator technique has been used in pattern recognition applications. We introduce a correlation performance measure, peak to background ratio (PBR), defined as the ratio of the peak intensity to the average background variation in a single correlation output. Using this performance measure, we analyze the binary correlator and show that the binarization of the images can result in better performance. We consider a real-time implementation of the binary correlator, using VLSI technology. The analytical results are supported by computer simulations.