Precise orbit determination of high-earth elliptical orbiters usingdifferenced Doppler and ranging measurements

Recent advances in NASA's Deep Space Network station calibration methods have led to renewed interest in the use of differenced radio metric data types for interplanetary navigation, particularly differenced Doppler and range. An orbit determination error analysis is described which compares the performance of these differenced data types when used in concert with conventional two-way Doppler for precise navigation for high-earth orbiters. Three highly elliptical orbits were investigated, with apogee heights on the order of 20000, 70000, and 156000 km. The analysis assumes that each orbiter's downlink antennas has no ground footprint limitation in the near apogee regime. Results indicate that the most significant navigational accuracy improvements are seen for the lowest altitude orbit by using differenced Doppler measurements in conjunction with two-way Doppler. The results for the two higher-altitude orbits, although less dramatic, suggest accuracy improvements can also be achieved when differenced range measurements are combined with two-way Doppler     

月球探测器天文测角/单程无线电时间差分测距/差分测速导航方法

月球探测器高精度导航技术是确保月球探测任务顺利实施的关键技术之一。当前,大多数月球探测器都是利用地面无线电进行导航和控制,但存在可测控弧段短、易受干扰等局限性,且对于月球背面探测,存在无法直接测控的不足。针对上述问题,提出了一种新的基于天文测角/单程无线电差分测距/差分测速的月球探测器组合导航方法。该方法使用了天文星光角距、探测器接收到的来自地面站或中继星的单程无线电时间差分测距和时间差分多普勒测速3种量测信息,可有效抑制星上时钟和频谱仪的时间和频率测量误差。收敛后的平均位置和速度估计误差分别为902.7 m和0.12 m/s,最大的位置和速度估计误差分别为1 548.2 m和0.24 m/s。仿真分析结果表明该方法具有较高自主导航精度。     

Random Error in ARGOS and SARSAT Satellite Positioning Systems

ARGOS and SARSAT are two satellite Doppler navigation systems in which low cost ground beacons transmit bursts of stable frequency signals. The Doppler shifted signals received by the satellite provide the positions of the beacons. The positioning error is dominated by a random component, due mainly to the short-term frequency stability of the beacon oscillator. Theoretical analysis and explicit expressions of the random errors are given.     

陆基超远程无线电导航发展研究

定位导航和授时(PNT)系统是保障现代社会正常运转必不可少的基础设施,为了提供可靠的PNT信息服务,需要研发不依赖于卫星导航的PNT系统。介绍了国内外陆基超远程导航系统的发展情况,提出了发展基于甚低频无线电信号的陆基超远程无线电系统架构、关键技术及发展建议,陆基超远程导航系统可以在卫星导航不可用时提供备份,对于构建冗余可靠的国家PNT体系、保障PNT信息的安全及可靠性具有重要意义。     

DF Vectoring: Application to Stationary Synchronous Satellites

Several methods of using an earth-based radio reference signal to determine the three-axis attitude of a synchronous satellite, and two types of spacecraft electronic systems (amplitude measurement and phase measurement), which obtain attitude and pointing information from the radio reference signal for orientating the spacecraft and for directing large-aperture antennas aboard the spacecraft are described. The earth-based radio reference signal also enables the electronic systems to determine angles to other ground stations with respect to fixed (reference) stations on the earth. These attitude- and angle-determining techniques are applicable to communications satellites, navigational satellites, and intersatellite data relay systems.     

Frequency-Dependent Ionospheric Refraction Effects on the Doppler Shift of Satellite Signals

Analysis of four-frequency satellite Doppler data has allowed the separation and measurement of frequency-dependent ionospheric contributions to the Doppler shift, providing information useful in the study of errors incurred when tracking radio signals through the ionosphere. These refraction errors affect the accuracy of navigational position fixes obtained by Doppler satellite tracking systems. Some measured ionospheric refraction errors reported here are of interest because their magnitudes are significantly greater than those heretofore predicted from theoretical considerations.     

Range Instrumentation Radars

The history of range instrumentation radars begins at the end of World War 11, with the SCR-584 radar. Since then, the use of instrumentation radars on ranges all over the globe has expanded greatly to gather metric performance data on aircraft, projectiles, missiles, and satellites. In this paper, key subsystem-level and system-level developments during the past decade are reviewed, including pulse-Doppler, digital range systems, calibration techniques, computer usage, and dualfrequency systems. Recently developed instrumentation radars from domestic and foreign sources are described as are three unique high-power large-aperture systems used for satellite and ballisticmissile measurements. The paper concludes by examining the likely requirements for instrumentation radars of the future.     

基于通用无线电外设的北斗信号仿真系统

研究了基于通用软件无线电外设(USRP)的北斗信号仿真系统。给出了北斗卫星电文的生成方式,使用Matlab读取星历信息并定义编码产生北斗卫星信号,并利用USRP实现北斗卫星电文的调制发射,利用接收机对该信号进行捕获接收,并对信号附加的多普勒频移进行仿真。最后通过接收机对仿真系统产生的信号进行接收验证。通过此仿真系统可更直观地研究北斗卫星信号,对研究北斗卫星导航系统具有一定的参考意义。     

Performance improvement for constellation SAR using signal processing techniques

A new concept of spaceborne synthetic aperture radar (SAR) implementation has recently been proposed - the constellation of small spaceborne SAR systems. In this implementation, several formation-flying small satellites cooperate to perform multiple space missions. We investigate the possibility to produce high-resolution wide-area SAR images and fine ground moving-target indicator (GMTI) performance with constellation of small spaceborne SAR systems. In particular, we focus on the problems introduced by this particular SAR system, such as Doppler ambiguities, high sparseness of the satellite array, and array element errors. A space-time adaptive processing (STAP) approach combined with conventional SAR imaging algorithms is proposed which can solve these problems to some extent. The main idea of the approach is to use a STAP-based method to properly overcome the aliasing effect caused by the lower pulse-repetition frequency (PRF) and thereby retrieve the unambiguous azimuth wide (full) spectrum signals from the received echoes. Following this operation, conventional SAR data processing tools can be applied to focus the SAR images fully. The proposed approach can simultaneously achieve both high-resolution SAR mapping of wide ground scenes and GMTI with high efficiency. To obtain array element errors, an array auto-calibration technique is proposed to estimate them based on the angular and Doppler ambiguity analysis of the clutter echo. The optimizing of satellite formations is also analyzed, and a platform velocity/PRF criterion for array configurations is presented. An approach is given to make it possible that almost any given sparse array configuration can satisfy the criterion by slightly adjusting the PRF. Simulated results are presented to verify the effectiveness of the proposed approaches.     

Navigation and landing [A century of powered flight 1903-2003]

Navigation and landing for the first half century of aviation fundamentally relied on radio-based electronic aids. The military began serious investigation of radio navigation during World War I. Up until WW II map reading, dead reckoning, and various means of radio direction finding were the primary methods of determining aircraft position. Since WWII a number of other navigation techniques, such as Doppler radar, radio inertial, pure inertial, aided inertial, and today's integrated GPS inertial, have been developed. Most of the inertial systems evolved from the military ICBM and subsequent space programs.     

Everyman's Doppler Satellite Navigation System

This paper describes a system of navigation by measurement of the Doppler shift in the radio transmissions from a near-Earth satellite, and simple equipment for making the measurements. It also shows that the current information which is needed by the navigator can be reduced to a number containing six decimal digits. Finally, it shows that the computations needed for the navigator to obtain a fix can be performed witlh the aid of tables that can be prepared at least 18 months in advance. Using these tables and a simple slide rule, but no other computational aids, a fix accurate to about 500 meters can be obtained in about 10 minutes. More accuracy can be obtained at the expense of time, or time can be saved at the expense of accuracy.     

卫星导航陆基增强系统设备许可体系研究

陆基增强系统(GBAS)是支持飞机精密进近的下一代无线电导航设备。目前,在世界上安装GBAS和提供GBAS服务的机场越来越多。中国已经研制了首套卫星导航GBAS着陆系统,然而并没有通过相关设备的认证许可,未投入实际的运行使用。因此,本文在分析FAA和Eurocontrol对GBAS设备许可的基础上,提出了一套完整的卫星导航路基增强系统设备许可体系的方案,为进行设备的认证许可提供引导,使得整个地面子系统满足安装选址要求、地面和飞行测试对功能和性能的验证要求,保证地面设备子系统经过安装调试后能够达到理想的工作状态。设备许可体系在未来卫星导航技术的发展中发挥着广泛的指导作用,有利于设备的运行、发展和管理。     

基于Starlink机会信号/INS的组合导航方法

针对全球卫星导航系统(GNSS)因频点单一、落地功率低、易受电磁干扰以及存在覆盖较差区域等潜在的被拒止或被干扰导致的导航系统性能降低甚至失效的问题,提出了一种基于星链(Starlink)机会信号融合惯性导航系统(INS)的飞行器动态组合导航方法。首先分析了星链信号体制,建立了基于星链星座卫星下行机会信号的瞬时多普勒定位观测模型,设计了一种基于频率细分的快速最大似然多普勒频率估计方法,然后建立了基于扩展卡尔曼滤波(EKF)的Starlink机会信号/INS的组合导航模型,并对该导航方法进行了实验及分析。结果表明,该方法可为飞行器提供长航时、连续、高精度的导航。动态飞行情况下,该方法可实现平均优于25 m的三维定位精度和平均优于0.1 m/s的速度估计精度,比相同观测时间下的惯导精度提高了1～2个数量级,显著提高了飞行器的导航精度,可为战略导航提供方法和技术支撑。     

Onboard trajectory equipment measurements

In past years, the onboard trajectory measurements complex (OTMC) was found in flight tests of flight vehicles (FV). The quick-release small-sized complex makes registration of the information of onboard systems, definition of trajectory parameters of FV, the information synchronization of onboard systems, and trajectory parameters. OTMC is used for the solution of the whole set of different tasks on estimation of the characteristics of FV and its onboard equipment. With the help OTMC in flight tests there solved the tasks of estimation: operation and accuracy characteristics of air navigation computing systems, inertial navigational systems, integrated navigational systems; SNS receivers, landing radio engineering systems, accuracy of flights under the standard takeoff patterns and landing, take-off and landing characteristics, accuracy characteristics of radars, corrections of high-altitude, fast-track parameters, systems of early warning of ground proximity etc     

Design and applications of airborne radars in the VHF/UHF band

The simultaneous need for ground penetration and high resolution dictates the use of frequencies less than 500 MHz for imaging ground penetrating radar (GPR) designs. It is possible to build such systems with good performance and yet not interfere with ground installations operating in the same bands. The total number of airborne GPR systems needed to saturate the market is small, (possibly less than ten), and so the buildup of noise in this spectral region occupied by these radars will be negligible. This is fortunate, since there is a clear need for such radars in such areas as humanitarian demining and unexploded ordnance (UXO) mapping. Some formal set of guidelines is needed beyond that given in Part 15 of the FCC regulations, which both recognizes the need for airborne UWB radar operations, and still protects licensed users in the band     

Medium PRF Performance Analysis

A discussion of various types of x-band airborne radars is presented together with their systematic development through the years to the present time. Starting with simple, low pulse-repetition frequency (PRF) radars for measuring radar-target range, airborne radar development proceeded with more sophisticated high PRF Doppler radars where radar-target range and range rate were measured simultaneously. The use of Doppler (frequency) in signal processing allowed the separation of moving from nonmoving targets (ground), enabling the detection of moving targets in the presence of ground clutter. More recent developments in waveform generation and selection has resulted in the development of medium PRF radars, whereby a greater degree of tactical flexibility in target detection is achieved by combining the desirable features of both low and high PRF radars. Part of the available literature gives an overview, together with a specific example of the design and performance of an airborne medium PRF radar. Here, however, the systematic evolution of these radars is emphasized and the necessary theoretical background is developed for their performance calculations. Modern day airborne radars may be equipped with all three modes of operation, low, medium, and high PRF, allowing the operator to utilize the mode best suited for the tactical encounter. Low PRF and high PRF radars have been described elsewhere and are given here primarily for the sake of completeness and for the necessary background for developing medium PRF radar equations. They are also needed for developing the reasons why medium PRF radars came into being.     

Mapping lightning channels in a thunderstorm by radar

The state of Georgia has experienced a number of tornados that occur without warning, and, in several cases have caused fatalities. Researchers at the Severe Storms Research Center (SSRC) of the Georgia Tech Research Institute (GTRI), Georgia Institute of Technology are attempting to detect tornado formation within severe thunderstorms occurring in the vicinity of Atlanta, Georgia, using non-radar sensors that may provide early tornado warning and provide cueing to existing National Weather Service (NWS) radars. The goal of these studies is to increase the warning time of tornado formation within the parent thunderstorm. GTRI researchers use real-time S-band Doppler weather radar data from three National Weather Service WSR-88D NEXRAD radars to complement the development of the non-radar tornado sensors. Three NWS Doppler radars provide severe weather surveillance coverage of the north Georgia area to determine if a thunderstorm contains the Doppler signature that indicates tornado formation. The radar data, displayed on a work station developed and optimized for tornado detection by the National Severe Storms Laboratory (NSSL), serves as ground truth data for the non-radar sensor development. GTRI can display cloud to ground (CG) lightning strikes, a capability provided by overlaying data from a national monitoring network onto the radar reflectivity map. GTRI also uses a local lightning direction finder (DF) system that supplies azimuth and range to the lightning strike. This paper discusses the early lightning channel research and the passive parasitic radar system being operated by the SSRC.     

Application of the Concept of Referenced Radio Navigation

This paper discusses referenced radio navigation, the concept whereby monitoring stations at known locations are used to calibrate out systematic errors in a navigation system. This concept is implemented by broadcasting calibration data to the navigating user for application as real-time corrections to the position fixes made by the user's basic navigation equipment. A method is suggested for the automatic transmission and receiver processing of the correction data. Referenced radio navigation overcomes many of the shortcomings generally associated with long-distance navigation systems, and can increase accuracy and repeatability significantly. The concept is particularly applicable to global navigation systems such as OMEGA, in which propagation or synchronization errors can contribute substantially to the system error budget.     

Precision Synchronization of Satellites in Inclined Orbits

Synchronization between an Earth station and a satellite in geostationary orbit can be accomplished by repeatedly transmitting sync burst signals and making small timing corrections. However, when a satellite is in an inclined nonsynchronous orbit, such as a navigation satellite, the problem is more complex due to the high relative velocity of the navigation satellite relative to the ground. One possible solution to the problem is examined by employing a satellite in geostationary orbit to communicate with the navigation satellite. It is shown that the uplink delay to the navigation satellite can be deduced to an accuracy of about 1 ns by making a single round trip transmission.     

基于PSO-ELM的卫星导航欺骗式干扰检测CSCD

近年来,卫星导航系统在军事监测、精细农业、交通监控、资源勘探、灾害评估等领域得到了广泛应用,但由于卫星导航信号结构公开且到达地面时强度微弱,卫星导航系统极易受到各种各样的干扰,其中欺骗式干扰因具有较强的隐蔽性,对卫星导航系统构成巨大的安全威胁。传统的欺骗式干扰检测方法大多采用单一参数进行检测,具有一定局限性。考虑到欺骗干扰源在欺骗过程中会引起一系列参数变化,构造了一个多参数输入的卫星导航欺骗式干扰检测模型,即将多个特征参数作为极限学习机(ELM)的输入,并通过训练和学习将真实信号与欺骗信号区分开,从而实现欺骗式干扰检测。同时,利用粒子群优化(PSO)算法优化ELM中的输入权值矩阵和隐层偏置,改善由于网络参数随机生成导致分类精度低的问题。仿真实验证明了该方法在卫星导航欺骗干扰检测方面的可行性和有效性。