Planetary radio astronomy experiment for Voyager missions

The planetary radio astronomy experiment will measure radio spectra of planetary emissions in the range 1.2 kHz to 40.5 MHz. These emissions result from wave-particle-plasma interactions in the magnetospheres and ionospheres of the planets. At Jupiter, they are strongly modulated by the Galilean satellite Io.As the spacecraft leave the Earth's vicinity, we will observe terrestrial kilometric radiation, and for the first time, determine its polarization (RH and LH power separately). At the giant planets, the source of radio emission at low frequencies is not understood, but will be defined through comparison of the radio emission data with other particles and fields experiments aboard Voyager, as well as with optical data. Since, for Jupiter, as for the Earth, the radio data quite probably relate to particle precipitation, and to magnetic field strength and orientation in the polar ionosphere, we hope to be able to elucidate some characteristics of Jupiter auroras.Together with the plasma wave experiment, and possibly several optical experiments, our data can demonstrate the existence of lightning on the giant planets and on the satellite Titan, should it exist. Finally, the Voyager missions occur near maximum of the sunspot cycle. Solar outburst types can be identified through the radio measurements; when the spacecraft are on the opposite side of the Sun from the Earth we can identify solar flare-related events otherwise invisible on the Earth.     

Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

The secular variation of the core field is generally characterized by smooth variations, sometimes interrupted by abrupt changes, named geomagnetic jerks. The origin of these events, observed and investigated for over three decades, is still not fully understood. Many fundamental features of geomagnetic jerks have been the subject of debate, including their origin internal or external to the Earth, their occurrence dates, their duration and their global or regional character. Specific tools have been developed to detect them in geomagnetic field or secular variation time series. Recently, their investigation has been advanced by the availability of a decade of high-quality satellite measurements. Moreover, advances in the modelling of the core field and its variations have brought new perspectives on the fluid motion at the top of the core, and opened new avenues in our search for the origin of geomagnetic jerks. Correlations have been proposed between geomagnetic jerks and some other geophysical observables, indicating the substantial interest in this topic in our scientific community. This paper summarizes the recent advances in our understanding and interpretation of geomagnetic jerks.     

Review of energetic (> 20 ke V) bremsstrahlung X-ray measurements from satellites

Worldwide maps of electron precipitation into the atmosphere can be obtained remotely with a unique separation of spatial and temporal variations by sensing from a satellite the bremsstrahlung X-rays produced in the atmosphere by the incident electrons. From X-ray measurements electron fluxes and energy spectra can be derived over a broad range of energies under both daytime and nighttime conditions. The technique was first demonstrated in 1972 and has now been used sucessfully in several programs. The most continuous and widespread coverage can clearly be achieved from high altitudes, but even at only a few hundred kilometers it has been possible to obtain mappings over a wide area since bremsstrahlung X-ray fluxes are often rather steady in time during the few minute duration of a low altitude satellite pass over the polar region. The satellite bremsstrahlung data already acquired have provided information on the long term morphology of the total fluxes and energy spectra of bremsstrahlung X-rays emitted from a large area and have shown that pronounced longitude structure commonly occurs in the X-ray emissions. The data have tended to be complementary in nature to that obtained by the more well established technique of measuring bremsstrahlung X-rays from balloons, whereby time variations can be studied in detail with more limited geographic coverage. From balloons it is known that the X-rays show a variety of time variations, but many of the faster microburst type phenomena have yet to be observed from satellites. The present status of satellite bremsstrahlung X-ray measurements is reviewed here, some of the key results summarized and suggestions made for future improvements in instrumentation. The review is limited to X-rays > 20 ke V and therefore to the associated precipitation of only the more energetic electrons.     

基于中继测量的环月探测器定轨能力分析

嫦娥四号月球探测拟首次实现月球背面的软着陆,测控与数传依赖地月L2平动点的中继卫星,并有望获取四程测量与星间测量数据。对基于中继测量的环月探测器测定轨能力进行了仿真分析,结果表明,中继卫星可较好地实现环月探测器连续跟踪;在定轨能力方面,中继卫星自身轨道精度是制约环月探测器定轨精度的重要因素,当跟踪弧段达到5h以上时,定轨精度趋于稳定,但轨道精度较中继卫星的轨道精度相差1个量级;对于星间链路测量,除中继卫星自身的轨道精度外,星钟的稳定性是制约定轨精度的另一个重要因素,如果辅助以每天1h的地基跟踪亦可实现优于百m的定轨精度。     

关于大行星（或月球）轨道器的冻结轨道

关于人造地球卫星的冻结轨道问题早已为人们所熟知，而且已有相应的卫星在轨运行。在考虑该冻结轨道形成时，主要依据地球扁率J3项与J2项的相对关系，这是由地球非球形引力场的特征所决定的，原理十分清楚，但其原理和结论不能随意地用于其他大行星(或月球)的轨道器。在一般情况下，对于低轨卫星形成冻结轨道的条件，非球形引力位中的奇次带谐项(J21 1，l≥1)将起重要作用。不仅仅是一个J3项，例如月球轨道器，J3，J5，J7和J9均有不可忽视的影响，而且与轨道倾角有一定的关系。为此，本文根据轨道理论对冻结轨道的存在性及其有关问题作进一步的分析，给将来的深空探测提供轨道设计的有关信息和依据。     

Overview of Commercial Satellite Communications

The period from Arthur Clarke's 1945 prediction of geosynchronous satellite communications covering the entire planet until satellites were stationed over the Atlantic, Pacific, and Indian Oceans was less than 25 years. In the following 15 year period, satellite communications has affected all of us. Most international calls are carried by satellite. Much of the television that we watch has been relayed, processed, or distributed by satellite. In fact, many of us who live in cabled cities can choose among 50 channels or more for viewing on a particular night, largely brought to us by satellite. Some morning papers, radio programs, and basic weather data appear coast to coast rapidly because of the satellite. Even while we sleep, computers in an increasing number of business offices are talking to each other by satellite. Virtually the whole world, from the busiest urban center to the most remote island, can be interconnected by satellite communications networks capable of providing economical and reliable transmission of communications signals, including voice, data, electronic mail, and video. The satellite's advantages of distance insensitivity, point-to-multipoint capability, and improved quality over long distances are unique. These facts have led Clarke to speculate on the future impact of satellite communications in The View from Serendip (1977): I submit . . . that the eventual impact of the communications satellite upon the whole human race will be at least as great as that of the telephone upon the so-called developed societies.     

The W-band data collection experiment of the DAVID mission

The data collection experiment (DCE) of the scientific mission DAVID (DAta and Video Interactive Distribution) of the Italian Space Agency (ASI) will pioneer the use of the W-band for telecommunications experiments. In particular the collection of high volumes of data from remote or virtually remote sites will be achieved through the exploitation of a W-band link in a time window of a few minutes per satellite pass. The experiment will hence demonstrate the capability of the W-band channel to be used reliably for a telecommunication link. At the same time, the experiment will provide useful elements for the characterisation of the W-band channel, in order to be able to design properly future operational systems working at W-band.     

A data transmission scheduling algorithm for rapid-response earth-observing operations

With the development of rapid-response Earth-observing techniques, the demand for reducing a requirements-tasking-effects cycle from 1 day to hours grows rapidly. For instance, a satellite user always wants to receive requested data in near real-time to support their urgent mis- sions, such as dealing with wildfires, volcanoes, flooding events, etc. In this paper, we try to reduce data transmission time for achieving this goal. The new feature of a responsive satellite is that users can receive signals from it directly. Therefore, the traditional satellite control and operational tech- niques need to be improved to accommodate these changes in user needs and technical upgrading. With that in mind, a data transmission topological model is constructed. Based on this model, we can deal with the satellite data transmission problem as a multi-constraint and multi-objective path- scheduling problem. However, there are many optional data transmission paths for each target based on this model, and the shortest path is preferred. In addition, satellites represent scarce resources that must be carefully scheduled in order to satisfy as many consumer requests as possible. To efficiently balance response time and resource utilization, a K-shortest path genetic algorithm is proposed for solving the data transmission problem. Simulations and analysis show the feasibility and the adaptability of the proposed approach.     

基于伪距信息的COMPASS-MEO导航卫星单星定轨分析

COMPASS-MEO导航卫星的伪距观测量包含星站距离、接收机钟差和卫星钟差以及各种噪声。本文首先分析了接收机钟差和卫星钟差在一定间隔内主要表现为线性变化的特性,可以考虑将接收机和卫星钟差作为测距的偏差和偏差变化率和轨道一起进行求解。其次,利用实测的MEO导航单星伪距数据,进行了数据预处理和定轨试验,分别对站间无时间同步信息和有时间同步信息两种情况进行定轨、残差分析和参数解算。使用重叠弧段、轨道预报和激光观测数据验证定轨结果的精度。结果表明,两种情况下的定轨结果无明显差别。该定轨方法可以运用于MEO导航单星精密轨道的计算。     

高轨目标掩星成像相位恢复技术研究

高轨目标掩星成像通过观测高轨卫星对恒星的遮掩过程,实现对高轨目标的成像.该方法采用望远镜线性阵列观测高轨目标遮掩恒星过程中恒星亮度变换,获得高轨目标在地面的投影,通过相位恢复方法可计算得到卫星轮廓图样,具有成像分辨力高,设备制造难度小等优点,在高轨目标成像领域具有较好应用前景.本文分析利用掩星成像方法对高轨目标成像的可行性,重点对掩星成像过程的相位恢复方法进行改进,根据掩星成像特点对输入输出算法进行优化,仿真结果表明：改进后的相位恢复方法可显著提高图像恢复质量和掩星成像方法的空间分辨力.     

基于双星系统的卫星几何学精密定轨方法研究

双星导航系统的建立，为我国实现自主的卫星天基测控技术提供了可能。同时由于其全天候、全天时、相对定轨精度高等特点可望成为一种低、中轨卫星精密定轨的有效手段。但由于双星系统中静止卫星数目仅有两颗，要得到低、中轨卫星的三维定位信息，还需要额外的第三维观测量。本文根据双星系统的现状，结合国内对低、中轨卫星精密定轨的要求，提出了一种基于双星系统的卫星几何学精密定轨的方法，概述了其基本原理及其组成，给出了卫星定轨的方法和数学模型，同时根据数据仿真分析了该定轨系统的定轨精度，为下一步工程实现提供了理论基础。     

A method for satellite time series anomaly detection based on fast-DTW and improved-KNN

In satellite anomaly detection, there are some problems such as unbalanced sample distribution, fewer fault samples, and unobvious anomaly characteristics. These problems cause the extisted anomaly detection methods are difficult to train accurate classification model, and the accuracy of anomaly detection is hard to improve. At the same time, the monitoring data of satellite has high dimension and is difficult to extract effective features. Based on the DTW over-sampling method, this paper realizes the over-sampling of fault samples in satellite time series, and constructs a distributed and balanced time series data set. The Fast-DTW method is applied to calculate the distance between different time series, which can improve the speed of similarity calculation. KNN (K-Nearest Neighbor) method is applied for classification and the best classification result is obtained by search the optimal hyper-parameters k. The results show that the proposed method has high anomaly detection accuracy and consumes short calculation time.     

Polarization Loss of a Satellite: Data Collection Sensor Link

Economy of data collection systems consisting of several widely dispersed sensor platforms monitored by satellite can be realized by using an inexpensive linearly polarized antenna on each platform. The polarization loss of such an antenna is calculated.     

ATS-6 Significance

The Applications Technology Satellite (ATS-6), the most powerful, most sophisticated, most versatile communications satellite flown to date, is the last of NASA's experimental satellites intended to demonstrate major advances in communications and spacecraft technology. It is a multipurpose, multidisciplinary spacecraft whose principal objectives were to demonstrate a large, unfurlable antenna structure and precise pointing and attitude control in the synchronous orbit The spacecraft carries 27 different experiments, 3 of which demonstrate users' applications of satellite communications. Significant advances in antenna technology, precise attitude control, materials technology, spacecraft structures, and thermal control have been successfully demonstrated. The most significant accomplishments of the ATS-6 mission are the demonstration of the practicality of satellite broadcasting to small, simple, inexpensive ground stations and the uses of this potential service in the solution of social problems involving education and health care. The success of these initial demonstrations has led ATS-6 experimenters and potential users to incorporate a Public Service Satellite Consortium dedicated to the provision of satellite broadcasting services for educational and health-care applications.     

Achieving higher levels of electronic integration throughsystem-on-chip

All aerospace vehicles have the common constraint of limited space for the electronic systems. The challenge has always been how to pack effective electronic systems into the space available. Higher levels of electronic integration can give a competitive advantage; for example, by providing extra channels in a communications satellite thereby increasing revenue to the operator. Today's deep sub-micron manufacturing processes for integrated electronics offer an opportunity for a step change for electronic functionality that can be packaged in a given space. This technology makes possible, for the first time, a true system-on-chip approach to electronic systems, which is already being exploited by the commercial sector in products such as the mobile telephone     

Global Gravity Field Recovery Using Solely GPS Tracking and Accelerometer Data from Champ

A new long-wavelength global gravity field model, called EIGEN-1, has been derived in a joint German-French effort from orbit perturbations of the CHAMP satellite, exploiting CHAMP-GPS satellite-to-satellite tracking and on-board accelerometer data over a three months time span. For the first time it becomes possible to recover the gravity field from one satellite only. Thanks to CHAMP'S tailored orbit characteristics and dedicated instrumentation, providing continuous tracking and on-orbit measurements of non-gravitational satellite accelerations, the three months CHAMP-only solution provides the geoid and gravity with an accuracy of 20 cm and 1 mgal, respectively, at a half wavelength resolution of 550 km, which is already an improvement by a factor of two compared to any pre-CHAMP satellite-only gravity field model. This revised version was published online in August 2006 with corrections to the Cover Date.     

发展单兵星敏导航装备的必要性及技术特点

星光导航不受电磁干扰、能提供绝对姿态信息，具有重大战略意义。目前的星敏主要是为空天基导航而发展的，将其应用于单兵导航是否必要、需克服哪些技术难点、能达到怎样的效果等，都是值得探索的问题。为此，首先论述了发展单兵星敏导航装备的必要性，包括：不受电磁干扰破坏，是其他单兵导航装备失效时的保底装备；定向精度高，能弥补单兵卫星导航装备无法定向的缺陷；已突破部分气象因素限制，具备了全天时导航条件等。然后探讨了单兵星敏导航与空天基星敏导航、卫星导航、天文大地测量等比较所具有的不同技术特点。提出了发展单兵星敏导航装备需解决的关键技术问题，包括：气象因素影响的消减、时间基准和电源的长期维持、系统探测性能与系统小型化的平衡等。研究结果可为发展单兵星敏导航技术、设计研制单兵星敏导航系统提供参考。     

Argos海洋浮标多普勒定位原理与方法

通过对海洋浮标进行定位,Argos系统在海洋科学方面得到较为广泛的应用。但Argos系统卫星过顶弧段甚短,加之信号发射周期较长,测量资料甚为稀疏,给海洋浮标的定位造成很不利的影响,容易出现矩阵奇异情况,造成定位失败。文章给出了有效的基于多普勒测量的用于数据收集发射平台的定位算法,并利用参考椭球面约束定位目标,从而改进定位算法,计算结果显示如果能有效的使用约束条件,可以使：①原先定位失败的情形成功解算;②原先定位成功的情形定位精度得到改进。文章还给出了针对海洋目标信标运动以及卫星星历误差等因素对定位结果造成的误差影响的统计分析。     

恒定应力无失效加速寿命试验可靠性分析方法

针对工程中缺少有效方法处理加速寿命试验中出现的无失效数据的情况,提出一种恒定应力水平下的无失效加速寿命试验可靠性分析方法.该方法首先将各个加速应力水平下的无失效寿命试验数据转换到正常应力水平,然后通过对正常应力水平下的无失效寿命数据进行分析,实现产品的可靠性评估与寿命预测.利用该方法对某型号卫星地球敏感器扰性枢轴的无失效加速寿命试验数据进行分析处理,结果表明该方法切实可行,能够充分利用各个加速应力水平下产品的无失效试验数据,较好地解决了产品进行无失效加速寿命试验的可靠性评估和寿命预测问题.