Genetic algorithm application to efficient utilization of the GSO

Utilization of the geostationary satellite orbit (GSO) has reached full capacity in orbital arcs at certain longitudes. A variety of proposals and regulations have already been established to increase the number of possible satellite positions. The optimum satellite arrangement carried out by considering the geographical distribution of service areas is an effective strategy for efficient utilization of the GSO. The genetic algorithm (GA) method is applied here to optimize the satellite arrangement. Initially, an example of the optimum arrangement of eight satellites is demonstrated by using the GA method to ensure accuracy of the newly developed program. Subsequently, a multiple beam satellite system concept is introduced to further improve the efficient utilization of the GSO. Finally, 80 satellites (40 service areas) in the ITU Region 1 example is solved using the GA method, resulting in a quasi-optimum satellite arrangement solution. By using the GA method, the quasi-optimum solution can be obtained by very short (e.g., several ten seconds) calculation times.     

Optical fiber geostationary tether satellite (F-GTS) system design

The geostationary satellite orbit (GSO) is a limited natural resource and its efficient utilization is very important. The geostationary tether satellite (GTS) system has a number of satellites aligned along the local vertical on either side of the nominal geostationary position. The system is synchronized with the Earth's rotation and all the various altitudes are geostationary, Furthermore, optical-fiber geostationary tether satellite (F-GTS) system has been introduced to improve the GTS system, with regard to increment of communication capacity, simplification of interference paths and intersatellite link (ISL) capability. The F-GTS system design is discussed with the purpose of achieving a realistic satellite network. Three frequency bands, i.e., the 14/11, 30/20, and 50/40 GHz bands, are examined for selection of the optimum frequency band. The F-GTS system example for covering the service areas in Japan is discussed with regard to satellite antenna diameter, communication capacities, etc. To apply the F-GTS system to the whole GSO, the diagonal azimuth orbit arrangement method is proposed for low latitude service areas. Moreover, the F-GTS communication capacity and total communication capacity, when the F-GTS systems are applied to the whole GSO, are also examined.     

The Advent of Land Mobile Satellite Service Systems

The practicality of providing cellular-type communications service to underserved remote areas of the country is now possible through the use of satellites in geostationary orbit. The advent of high-power, land-mobile satellites, coupled with high-performance, low-cost ground receivers, makes it possible to provide mobile radio, mobile telephone, data communication, and other services to large numbers of rural and suburban users. A recent Federal Communications Commission (FCC) decision has allocated L-band (1.5 GHz, 1.6 GHz) spectrum to this service. Even though there is a significant amount of spectrum available at L-band, the expected demand for this service is high and spectral efficient means must be devised to maintain sufficient capacity. Expedient means used to increase capacity, in the absence of additional spectrum, are single channel per carrier, demand assignment multiple access (SCPC-DAMA) with voice, frequency reuse via multiple beams, and orbital reuse by using multiple satellites. Some of the operational, systemic, and technological considerations of the first generation land mobile satellite service (LMSS) that would provide thin-route services to large land masses of North America are considered here.     

低轨卫星可控式冗余分包遥测技术

随着卫星功能日趋复杂,遥测参数越来越多,处理要求越来越快,遥测设计面临越来越大的压力,必须拓展新的设计思路.本文讨论了一种低轨卫星可控式冗余分包遥测技术,更好地缓解遥测信道“瓶颈”,满足用户多样化的遥测需求,提高卫星遥测能力.该设计采用PCM（Pulse Code Modulation,脉冲编码调制）遥测和分包遥测相结合的方案,在信道资源有限,遥测参数庞大、用户需求多样的约束条件下,通过星载软件模式控制的方法实现了动态可编程遥测处理和遥测数传通道的冗余处理,提高了遥测信道的资源利用率、遥测设计的灵活性和系统的可靠性,该技术已成功应用于某在轨卫星,并被多颗在研卫星所采用.     

空间信息网络中面向双卫星的频谱共享方法

认知无线电能为缓解空间信息网络中日益增长的服务需求与紧张的频谱资源之间的矛盾提供有效的解决途径。论文针对静止轨道卫星系统和低轨道卫星系统提出一种基于频率动态分配的频谱共享方法。基于用户信号质量最差场景的干扰分析，定义波束隔离区域以避免同频干扰。此外，针对卫星运动引起的时空动态性，通过卫星星历、频率配置方案以及天线方向图等共享信息来预测可能出现的干扰，在此基础上提出频率动态分配算法来实现频谱共享。仿真结果表明，频谱共享方法在保护主用户的同时可有效提高次级用户的信号质量。     

14.5-14.8 GHz Frequency Sharing by Data Relay Satellite Uplinks and Broadcasting-Satellite Uplinks

Data relay satellites are being developed to provide real-time data links between research satellites in low earth orbits and central data acquisition and processing facilities. Frequency assignments for data relay satellite links will be made in bands allocated internationally to the space research service. One of the bands which will be used lies between 14.5 and 15.35 GHz, where the space research service has had a frequency allocation as a secondary service since 1971. During the General World Administrative Radio Conference of the International Telecommunication Union, held in Geneva in 1979, a primary frequency allocation was made in the band 14.5-14.8 GHz to the fixed-satellite service, specifically for use by earth-to-space links of the broadcasting satellite service. The feasibility of shared band operation is evaluated between data relay satellite uplinks and broadcasting-satellite feeder links in the band 14.5-14.8 GHz. Relationships for predicting interference power levels are formulated, as functions of satellite separation and of earth station separation. Tradeoffs between satellite separation angle and earth station separation are explored, and conclusions are drawn regarding the feasibility of band sharing. Co-channel operation is demonstrated to be technically feasible for typical systems, provided appropriate separations are maintained.     

Geostationary tether satellite system and its application tocommunication systems

The geostationary tether satellite system expands the geostationary orbit resource from a one-dimensional arc into a two-dimensional disk. The tethered satellites, each several thousand kilometers apart and aligned along the local vertical, are stabilized at the altitude of the geosynchronous orbital speed. When this system is applied to communications systems, it is estimated that the number of satellites can be increased as much as thirteenfold and the communication capacity can be increased more than seventeenfold, compared with a conventional geostationary satellite orbit system     

Optical Calibration of Geostationary Satellite Tracking Systems

A precise calibration method for range and angle observation has been developed for eliminating the systematic error of tracking systems, thus improving the accuracy of orbit determination for geostationary satellites. The principle of calibration is based on an orbit determination employing a point of optical angle observation in addition to radio tracking observation, in which we estimate observation bias parameters simultaneously with orbital elements, including the effects of geodetic mismodelings. As shown by an actual calibration experiment in our ground station, orbit determinations is sufficiently accurate that the error of predicting satellite range falls within a few meters at four days after the day of orbit determination.     

Satellite communication system integrated into terrestrial ISDN

This paper presents an advanced satellite communication system named DYANET II. This system uses satellite channels as subscriber lines for ISDN customers as well as trunk circuits for overflow traffic. The system can offer the same ISDN services to satellite customers as those available to terrestrial subscribers in terms of numbering, signaling, and charging systems as well as user-network interfaces. It can also set up satellite channels on a demand assignment basis to achieve efficient satellite channel utilization, and to connect customers by single-hop satellite connections. A compact, lightweight Earth station has been developed for remote customers and temporary demands such as exhibitions.     

Collision between Satellites in Stationary Orbits

The collisions between stationary satellites, and those between a stationary satellite and abandoned stationary satellites which have nearly synchronous orbits with relatively large inclination are discussed. A general formula is introduced for calculating the probability of collision, as a function of time, three-dimensional sizes, orbital bounds, and numbers of satellites. Numerical calculation shows that the probability of collision is negligible if the sizes and numbers are comparable to those of existing satellites, whereas collision is possible for larger size, e.g., for a huge hypothetical gigawatt solar power satellite. The possibility would become large if the satellites continued to increase in number and to be abandoned in the stationary orbit at the present rate over a century, even if the size is ordinary, such as several meters.     

双线程滑动窗口多系统GNSS超快精密定轨实现及评估

全球导航卫星系统（GNSS）超快精密定轨为GNSS实时应用提供了高精度空间基准。基于天地协同定位、导航与授时（PNT）网络服务中心实现了四系统GNSS卫星超快精密定轨,并对定轨结果进行精度评价。介绍了天地协同PNT网络的概念内涵以及网络服务中心部署的超快精密定轨软件架构和详细功能,并针对实时应用需求提出了一种双线程滑动窗口超快精密定轨策略。最后利用重叠弧段比较、与外部轨道产品比较以及卫星激光测距（SLR）检核3种方式对定轨结果进行了精度评价。结果表明,与武汉大学分析中心的最终事后精密轨道产品相比,四系统GNSS MEO卫星预报6 h弧段的径向均方根（RMS）误差整体在2~5 cm水平,BDS2 IGSO卫星最小一维RMS误差在10~15 cm水平;GPS和Galileo卫星的SLR检核残差均值在1~3 cm水平,标准差在3~6 cm水平,能够满足后续厘米级实时应用对空间基准的精度需求。     

基于非合作低轨卫星的测向交叉定位技术

根据非合作低轨卫星的特点，可以被动测量多颗卫星信号的来向，通过测向交叉的方式进行定位。但是通过星历解算出的卫星位置位于地心地固坐标系，用户测量的方位角和俯仰角基于站心坐标系。针对非合作低轨卫星测向交叉定位时目标用户角度信息与卫星位置基于不同坐标系的问题，提出了一种迭代最小二乘定位算法，通过迭代的方式不断收敛定位结果，能够在目标用户角度信息与卫星位置基于不同坐标系的情况下，解决非合作低轨卫星的测向交叉定位问题。仿真结果表明，基于迭代最小二乘定位算法能够实现非合作低轨卫星仅利用角度定位，并分析了测角精度、卫星轨道高度、参与定位卫星数与定位误差之间的关系。针对迭代的计算方法，分析了迭代过程中不同收敛条件下迭代次数与定位误差之间的关系。在保证定位精度的情况下，将迭代收敛范围设置为8~30 km，可以降低2~3次迭代次数。     

Basic performance of BeiDou-2 navigation satellite system used in LEO satellites precise orbit determination

The visibility for low earth orbit（LEO） satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system（GPS）. In addition, the spaceborne receivers＇ observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satellites orbits. The precise orbit determination（POD） results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional（3D） accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about30 cm. As for the precise relative orbit determination（PROD）, the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demonstrates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit（GEO） satellites is illustrated for POD.     

Position-fixing using the USSR's GLONASS C/A code

The possibility of the USSR's global satellite navigation system GLONASS and the NAVSTAR Global Positioning System using a common navigation system can only be determined following exhaustive testing of two systems in a variety of satellite and receiver modes and configurations. The authors describe their first attempts to carry out basic position-fixing and timing measurements with a single-channel, sequencing digital receiver in a C/A code phase-measurement mode using the GLONASS satellites. The receiver used to produce the fixes was a digital sequencing unit with a single stage of downconversion and followed by 1-bit quantization. Code acquisition was accomplished using 1-Q channels measuring code phase. The number of satellites available in the present preoperational phase heavily restricts the time and satellite configurations which can be tested. However, the results have encouraged the authors to propose a range of experiments aimed at evaluating the two systems and eventual integration     

北斗实时精密轨道和钟差产品解算策略及精度评定

随着北斗卫星导航系统全球星座部署即将完成，其应用领域不断扩大，实时精密服务性能受到了极大关注。基于动力学精密定轨方法，设计了北斗卫星实时轨道、钟差算法流程和解算策略。利用不同频点信号，分别计算了BDS-2和BDS-3卫星的实时精密轨道和钟差，建立了完整的轨道和钟差精度评定方法，重点对解算的实时产品的精度进行了评定。结果表明：BDS-2和BDS-3实时精密轨道和钟差产品精度均可满足大部分实时用户的需求。对于B1IB3I频点，BDS-3 MEO卫星的实时轨道精度约为26cm，径向精度约为6cm，实时钟差精度约为0.45ns，且相较于BDS-2，性能更加稳定；对于B1CB2a频点，BDS-3 MEO卫星的实时轨道精度优于20cm，精度和稳定性较高。     

Irregular Satellites in the Context of Planet Formation

All four giant planets in the solar system possess irregular satellites, characterized by large, highly eccentric and/or highly inclined orbits. These bodies were likely captured from heliocentric orbit, probably in association with planet formation itself. Enabled by the use of large-format digital imagers on ground-based telescopes, new observational work has dramatically increased the known populations of irregular satellites, with 74 discoveries in the last few years. A new perspective on the irregular satellite systems is beginning to emerge.We find that the number of irregular satellites measured to a given diameter is approximately constant from planet to planet. This is surprising, given the radically different formation scenarios envisioned for the gas giants Jupiter and Saturn compared to the (much less massive and compositionally distinct) ice giants Uranus and Neptune. We discuss the new results on the irregular satellites and show how these objects might be used to discriminate amongst models of giant planet formation.     

面向高轨空间的北斗导航性能增强星座选型研究

由于高轨空间超出北斗卫星导航系统的正常服务区域,导航信号微弱、可见性差,难以实现高轨飞行器全程稳定可靠的导航定位服务。提出了以空间卫星为时空基准传递平台,向高轨空间区域发射导航信号,从而提高高轨飞行器导航性能的方法,并展开面向高轨空间的北斗导航性能增强星座选型研究。基于卫星可见性、精度衰减因子（DOP）、信号接收门限和所需增强卫星数目等评估指标,仿真分析了基于LEO星座、MEO星座和HEO星座的北斗导航增强性能。     

太阳同步卫星双星组网维持策略

某准共面星座由两颗相位差为 180°的太阳同步卫星组成。在对其进行轨道维持时 ,需综合考虑相位差和地面轨迹范围两方面的限制。然而 ,由于这两颗卫星的轨道倾角存在差异 ,使得在轨道维持过程中不能同时满足相位差和地面轨迹的要求。为解决上述问题 ,本文提出了调整地面参考轨迹的方法 ,实践证明有效。     

ATS-6 Radio Frequency Interference Measurement Experiment

The frequency band from 5.925 to 6.425 GHz is served by fixed satellites and by terrestrial microwave links. There is a possibility of microwave links pointed at the horizon causing interference to the uplinks of domestic and international communications satellites sharing the same frequency band. A mathematical model has been derived for predicting the fields at geostationary orbit based on the known characteristics and known distribution of the terrestrial microwave relay system. The Applications Technology Satellite-6 (ATS-6) is sensitive to signals in the range of 10 dBW radiated in the direction of the satellite. Signals in the range of 10-30 dBW have been recorded over various parts of the United States.     

Detecting near collisions for satellites

A highly efficient algorithm is presented for detecting near collisions involving satellites. Rather than examine all possible pairings of a satellite with another orbiting object, the new approach examines trajectories at a sequence of coarse time steps. Objects which are spatially isolated cannot be involved in a collision, and are discarded. The time steps, orbit calculations, and discarding are repeatedly refined until the only remaining objects experience near collisions.