Geostationary Communication Satellite Research Articles

Microwave holography measurement and adjustment of 25‐m radio telescope of Shanghai

AbstractIn an attempt to measure and correct the surface profile of the Sheshan 25‐m radio telescope, the author carried out a phase coherent holographic experiment at 12.26 GHz with a geostationary communication satellite SINO‐1 in the far field. To improve the spatial resolution, the author took the drift of the communication satellite into consideration. For the backend, a digital cross correlator was used to measure the complex beam pattern of the antenna under test. According to the data collected in the experiments, the holography software can give the energy distribution map, error map, and a suggested adjustment for every junction of the panels, after four iterations of measurement and adjustment in a week, the surface accuracy of the antenna is improved from 0.948 mm to better than 0.5 mm. The experiment shows that the microwave holography is much faster and more convenient than traditional method. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 467–470, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22171

Emerging commercial opportunities based on combined communication–navigation services

Cost reduction pressure on companies and increasing regulatory and legislative demand together with rapid technological progress in space-based communication and navigation are opening up new and exciting commercial opportunities. In this framework, a novel service for maritime applications is presented using a two-way messaging system and the global navigation satellite system (GNSS). The system implements an end-to-end solution for asset tracking and fleet management, positioning and tracing, messaging and security for all types of sea-going vessels. The service applies a vessel-based terminal hosting a GNSS receiver which transmits the navigation status together with messages to a Service Center with a flexible return-link capability. A hybrid space segment is considered comprising the Inmarsat constellation of geostationary communications satellites augmented by two highly inclined low earth orbit satellites for truly global services. Services will be offered to commercial enterprises such as fishing companies as well as public entities such as National Coast Guards. A detailed market analysis has been performed to assess these markets and to determine their penetration. Commercial viability has been proven for business models purely based on Inmarsat and a hybrid space segment using Inmarsat and dedicated micro-satellites. Both cases represent viable businesses in the range of MEUR 100 p.a. Although tailored to a specific market, the approach can be extended to other commercial opportunities requiring space-based communication–navigation services.

정지궤도 위성의 자동운용을 위한 위치결정 시스템의 개념연구

현재 240여기의 상업용 정지궤도 통신위성이 운용 중에 있지만, GPS 등의 위치항법 위성의 고도보다 높을 뿐만 아니라 나쁜 가시성으로 인하여 중궤도 위치항법시스템을 사용할 수 없으므로 반드시 지상관제소에 의해 추적되어야 한다. 또한 지상관제소에서 관측할 경우 정지궤도 위성은 거의 움직이지 않는 것처럼 보이기 때문에 수 미터급의 정지궤도위성의 위치결정 정밀도를 높이기 위해서 충분히 멀리 떨어진 2곳 이상의 추적안테나를 사용하여야 한다. 따라서 본 논문에서는 정지궤도 위성의 궤도결정과 자동운용을 위해서 정지궤도 고도보다 높은 2일 주기의 원형궤도를 사용하는 GSPS(Geostationary Satellite Positioning System)을 제안하였다. GSPS는 지상추적소에서 정밀하게 위치가 결정된 자기 자신의 위치정보 및 시각정보, 보정데이터와 정지궤도 위성의 운용을 위한 명령을 GSPS 위성에 전송하여 정지궤도위성에 위치정보를 제공하는 기능을 한다. Even more than 240 commercial geostationary communication satellites currently on orbit at the higher location than the GPS orbit altitude perform their own missions only by the support of the ground segment because of weak visibility from GPS. In addition, the orbit determination accuracy is very low without using two or more dedicated ground tracking antennas in intercontinental ground segment, since the satellite hardly moves with respect to the ground station. In this paper, we propose the GSPS(Geostationary Satellite Positioning System) in circular orbits of two sidereal days period higher than the geosynchronous orbit for orbit determination and autonomous satellite operation. The GSPS is conceived as a ranging system in that unknown positions of a geostationary satellite can be acquired from the known positions of the GSPS satellites. Each GSPS satellite transmits navigation data, clock data, correction data, and geostationary satellite command to control a geostationary satellite.

정지궤도 통신위성의 원격측정명령처리기 기술모델 열해석

정지궤도 통신위성 원격측정명령처리기의 기술인증모델 개발을 위하여 기술모델의 열 설계변경 및 해석을 수행하였다. 보드레벨의 소모전력량 측정치와 열주기시험의 결과를 활용하여 기술모텔에 대한 열해석모델을 개발하였다. 발열소자의 열소산 모델링은 인쇄회로기판에 투영된 소자의 footprint를 생성하고 그 표면의 전 영역에 균일하게 열소산량을 가하였다. 열설계변경(안)에 따라 설계변경 후 기술인증수준의 열진공환경에서 소자온도를 예측한 결과, CTU의 모든 소자들의 접합온도는 허용온도 이내로 존재하였다. Thermal design changes and analysis on the engineering model of Command Telemetry Unit(CTU) for a geostationary communications satellite arc performed for the purpose of developing an engineering qualification model. A thermal model is developed by using power consumption measurement values of each functional board and thermal cycling test results. In modeling heat dissipated EEE parts, heat dissipation is imposed evenly on the EEE part footprint area which is projected to the printed circuit board. All the EEE parts of CTU meet the requirement of their allowable temperature range when placed on the engineering qualification level of thermal vacuum environments in accordance with the proposed thermal design changes.

静止衛星通信回線を利用したネットワークRTK-GPSシステムの構築に関する研究

The accuracy of a few centimeters can be easily obtained in 2drms of the horizontal positions by RTK-GPS positioning. It is necessary, however, to provide the carrier phase data from a reference station located at a known position, to a user receiver. It is hard to purchase the expensive GPS receiver for RTK-GPS. So, the RTK-GPS users in Japan have desired the development of a more flexible, wider and less expensive carrier phase data dissemination service for a long time. In Japan, the area correction parameter FKP (flachen-korrectur-parameter; Geo++ in Germany) method has been well tested and evaluated through many projects nationwide, such as the mobile/cellular phone of the dual directional communication. Now, using the SuperBird geostationary satellite communication line, correction data transfer for the user station has tested on the RTK-GPS positioning at a fixed point before for the network-based RTK-GPS test. The SuperBird line can be disseminated the data for the wider area and the great many users simultaneously. The authors tried the RTK-GPS positioning using the correction data transmission via the SuperBird line. The investigated the RTK-GPS positioning at a fixed point in the Tokyo University of Marine Science and Technology about 5 km from the reference station. The 2drms in the horizontal positions are similar to the traditional RTK-GPS. And we must improve for the network-based RTK-GPS precise positioning in order for it to be used by the most people more easily.

통신탑재체와 소프트웨어 위성버스체를 통합한 HITL 시뮬레이터의 설계 및 구현

국가우주개발 중장기 계획의 일환으로 "통신방송위성(CBS: Communications and Broadcasting Satellite) 탑재체 개발 사업"이 한국전자통신연구원을 중심으로 국내산업체와 공동으로 추진되었다. 통신탑재체는 Ku대역 및 Ka대역 통신중계기와 안테나로 구성되며, 2000년 5월부터 2003년 4월까지 3년 동안 기술검증모델 탑재체가 개발되었다. 본 사업에서 통신방송위성을 위한 위성버스체는 개발되지 않으므로 위성을 이루는 통신탑재체와 버스체의 구성이 완벽하지 않았다. 이러한 문제를 해결하기 위해 위성버스체를 대신할 소프트웨어 위성시뮬레이터의 개발이 요구되었다. 개발에 적용된 위성버스체는 무궁화위성 버스체를 그 대상 모델로 가정하였다. 독립적으로 존재하는 하드웨어 통신탑재체와 소프트웨어 위성시뮬레이터의 연동은 통신탑재체의 기능 시험 및 검증을 목적으로 개발된 전기적 지상시험장치(EGSE: Electrical Ground Support Equipment)의 전력, 원격명령 및 원격측정 시스템(PCTS: Power, Command and Telemetry System)을 통해 이루어지도록 설계되었다. 이러한 시스템 개발을 통해 하드웨어 통신탑재체와 실시간으로 연동되는 Hardware-in-the-loop(HITL) 통신방송위성 시뮬레이터(CBSSIM: CBS Simulator)를 구현하였다. CBSSIM의 위성버스체 모델은 모멘텀 바이어스 삼축 안정화 방식의 정지궤도 위성이고, CBSSIM은 PCTS와 TCP/IP로 연결되고, 통신탑재체는 DC하니스 및 MIL-STD-1553B로 PCTS와 연결된다. CBSSIM은 실시간 처리부을 통해 통신탑재체와 위성버스체 모델로 원격명령을 전송하며, 통신중계기로부터 실제 원격측정 자료와 위성버스체 모델로부터 생성된 원격측정 자료를 수집한다. CBSSIM은 다양한 그래픽 사용자 인터페이스(GUI: Graphic User Interface)를 통해 위성의 상태를 감시할 수 있으며, 통신위성의 발사 전후 및 궤도 운용시의 상태를 모사할 수 있다. 본 논문에서는 객체지향 기법에 의해 위성버스체를 모사한 CBSSIM과 통신탑재체 및 통신탑재체와 CBSSIM을 연동시키는 PCTS를 포함한 HITL시뮬레이터의 설계 및 구현 내용에 관해 기술한다.에 관해 기술한다. Engineering qualification model payload for a communications and broadcasting satellite(CBS) was developed by ETRI from May, 2000 to April, 2003. For. the purpose of functional test and verification of the payload, a real-time hardware-in-the-loop(HITL) CBS simulator(CBSSIM) was also developed. We assumed that the spacecraft platform for the CBSSIM is a geostationary communication satellite using momentum bias three-axis stabilization control technique based on Koreasat. The payload hardware is combined with CBSSIM via Power, Command and Telemetry System(PCTS) of Electrical Ground Support Equipment(EGSE). CBSSIM is connected with PCTS by TCP/IP and the payload is combined with PCTS by MIL-STD-1553B protocol and DC harness. This simulator runs under the PC-based simulation environment with Windows 2000 operating system. The satellite commands from the operators are transferred to the payload or bus subsystem models through the real-time process block in the simulator. Design requirements of the CBSSIM are to operate in real-time and generate telemetry. CBSSIM provides various graphic monitoring interfaces and control functions and supports both pre-launch and after-launch of a communication satellite system. In this paper, the HITL simulator system including CBSSIM, communications payload and PCTS as the medium of interface between CBSSIM and communications payload will be described in aspects of the system architecture, spacecraft models, and simulator operation environment.

정지궤도 통신위성의 CCSDS 원격명령 암호복호기 구현

본 연구에서는 정지궤도 통신위성의 보안을 위해 CCSDS 원격명령(Telecommand) 암호복호기를 구현하였다. CCSDS 원격명령 데이터링크(Datalink)의 보안 기밀성(Confidentiality)을 위해 데이터링크 계층(Layer)내의 트랜스퍼 부계층(Transfer Sublayer) 다음에서 암호화를 행하는 Option-A를 선정하고 64-비트 코드블록(Codeblock)에서 56-비트 데이터 비트의 암호화를 위해 DES CFB 모드를 사용하였다. A54X32 FPGA에 구현된 DES CFB 로직은 원격명령 암호복호기의 기능 검증을 위한 인터페이스 및 제어 로직과 함께 PCB 보드에 구현하였다. 기능시험용 PC를 사용하여 암호화된 원격명령을 생성하고 암호복호기에 전송한 뒤 복호화한 뒤 기능시험용 PC에 피드백하고 전송한 코드블록과 비교한다. 수행코드에 해당하는 릴레이 구동에 의한 LED ON 동작 및 측정된 코드블록 파형과 시뮬레이션 파형의 비교를 통해 원격명령 암호복호기의 기능을 검증하였다. In this paper, a CCSDS(Consultative Committee for Space Data Systems) telecommand(TC) decryptor for the security of geostationary communications satellite was implemented. For the confidentiality of CCSDS TC datalink security, Option-A which implements the security services below the transfer sublayer was selected. Also CFB(Cipher Feedback) operation mode of DES(Data Encryption Standard) was used for the encryption of 56-bit data bits in 64-bit codeblock. To verify Decryptor function, the DES CFB logic implemented on A54SX32 FPGA(Field Programmable Gate Array) was integrated with interface and control logics in a PCB(Printed Circuit Board). Using a function test PC, the encrypted codeblocks were generated, transferred into the decryptor, decrypted, and the decrypted codeblocks were transmitted to the function test PC, and then compared with the source codeblocks. Through LED(Light Emitting Diode) ON operation by driving the relay related to Op-code decoded and the comparison between the codeblock output waveforms measured and those simulated, the telecommand decryptor function was verified.

Real time numerical dynamic orbit determination of geostationary satellite for time synchronization service

A real time numerical orbit determination method has been developed for a precise domestic time synchronization service. A one-way time synchronization method via a geostationary communication satellite was used. A differential method was also applied to mitigate errors. A numerical dynamic orbit determination method with a two-step estimator algorithm was implemented to further improve the differential mode time synchronization service through a more accurate acquisition of the geostationary satellite position. Perturbation force models were applied for the satellite dynamics, which include non-spherical geo-potential perturbations, lunar-solar perturbations, and solar radiation pressure. The reference stations for orbit determination were composed of four calibrated stations. Simulations were conducted to verify the performance of the proposed real time numerical orbit determination technique. The results verified that this technique made it possible to estimate real time position of a geostationary satellite within an accuracy of 2 km error in a spheroid radius. This performance demonstrates that the time accuracy is better than 40 nano seconds in the southern area of the Korean-peninsula. The real time numerical orbit determination method developed in this study can provide a reliable, highly accurate time transfer service through the establishment of domestic-only benchmarks.

Multi-Objective Optimization of Communication Satellites with Two-Branch Tournament Genetic Algorithm

In spacecraft design, many specialized state-of-the-art design tools are employed to optimize the performance of various subsystems. However, there is no structured system-level concept-definition process. Consequently, designers usually compromise some mission goals to satisfy only one of the primary design objectives. The conceptual stage of the spacecraft design process is formulated into a multi-objective discrete optimization problem. The use of multi-objective design allows the designer to evaluate different design alternatives across the whole set of design objectives. This work addresses two key design objectives for the spacecraft design process: the minimization of total launch mass and the maximization of spacecraft overall reliability. To predict values for the objective and constraint functions, a satellite design tool, which includes a satellite sizing model and a deterministic reliability model, was built and integrated with a genetic algorithm that employs a two-branch tournament to address the dual objective problem. The multi-objective approach was successful in determining sets of discrete design parameters that would minimize the launch mass as well as maximize the reliability of a geostationary communication satellite, using specified payload requirements. The designs generated by this approach appear to fall into three regions of the tradeoff space between the satellite launch mass and the satellite reliability objectives.

Estimation of Minimum Separation of Geostationary Satellites for Satellite-Based Augmentation System (SBAS) from Equatorial Ionospheric Scintillation Observations

In Satellite-Based Augmentation Systems (SBAS), the correction messages are transmitted to the users' receivers via geostationary communication satellites (GEOS) at GPS L1 (1575·42 MHz) frequency. Severe scintillations in the equatorial zone disrupt geostationary satellite links even at L-band. Observations of scintillations at 1·5 GHz from Calcutta (22·58°N, 88·38°E geographic, 32°N magnetic dip), located near the crest of the equatorial anomaly in the Indian zone, show that scintillations occur in patches of duration varying from a few minutes to several hours. During the solar maximum years 1998–2000, severe scintillations (Scintillation Index [ges ]15 dB) were recorded for 48 hr 55 min (1·27%) out of the total observation time of 3868 hr 9 min in the local time interval 19 to 00 hrs. In order to have a fail-safe system, it is suggested that more than one geostationary satellite be used in SBAS so that, if one link is disrupted, the other can be used for transmission of correction messages to the GPS users. The minimum longitudinal separation between two GEOS required for reliable operation of SBAS has been estimated, from the cumulative distribution of scintillation patch duration, to be 57° in the Indian longitude zone.

The geostationary orbit and satellite communications: concepts older than commonly supposed

The first proposal for a radio-equipped, man-made satellite in geostationary orbit is customarily attributed to author Arthur Charles Clarke (1917-), however, he makes no claim to having originated the geostationary orbit. Clarke's now classic article, in the October 1945 issue of Wireless World described a system of worldwide broadcasting via three satellites in geostationary orbit. In the article, Clarke listed seven references, including two to previous significant works by Willy Ley (Rockets, first published in 1944) and Hermann Noordung (The Problems of Space Travel, published in 1929). Both these works make reference to the geostationary orbit but as Clarke (see IEEE Spectrum, vol. 31, no.3, p. 4 et seq., Mar. 1994) points out the concept predates these works. It goes back at least to the works of Konstantin Eduardovich Tsiolkovsky (1857-1935), a Russian scientist now regarded as the father of space research. His book, (Dreams of Earth and Sky), published in 1895, was the first by a scientist on the subject.

A solar cycle of spacecraft anomalies due to internal charging

Abstract. It is important to appreciate how the morphology of internal charging of spacecraft systems, due to penetrating electrons, differs from that of the more common surface charging, due to electrons with lower energy. A specific and recurrent anomaly on a geostationary communication satellite has been tracked for ten years so that solar cycle and seasonal dependencies can be clearly established. Concurrent measurements of sunspot number, solar wind speed and 2-day >2 MeV electron fluence are presented to highlight pertinent space weather relationships, and the importance of understanding the complex particle interaction processes involved.Key words. Magnetospheric physics (energetic particles; trapped; solar wind – magnetosphere interactions) – space plasma physics (spacecraft sheaths, wakes, charging)

The proposed Ku-band non geostationary communication satellite systems

At the 1997 World Radio Conference France was able to secure agreement for Alcatel-Alsthom to launch a non-geostationary satellite system (called SkyBridge) operating at Ku-band, and utilizing the same spectrum as employed by the existing Ku-band geostationary satellites. Provisional power flux density limits for the level of unwanted interference into existing satellite and ground antennas were also adopted and are presently being reviewed by an ITU-R Joint Task Group. SkyBridge subsequently petitioned the U.S. Federal Communications Commission for a license to operate in the United States, causing the FCC to open a window for others to file for such systems. Five new filings were received and this paper describes the six (including Sky-Bridge) designs that have now been proposed. The paper discusses some of the relative merits of the various designs and also the issues of a) interference with the existing geostationary satellites (which may be solvable albeit with the latter losing some capacity) and b) mutual interference among NGSO systems (which may not be solvable in a manner acceptable to their proponents).

Rain rate distributions for China from hourly rain gauge data

Rain rate cumulative lognormal and Gamma distributions are calculated from hourly rain gauge data collected in 1991 at 333 locations in China. The Gamma distribution better represents the statistical rain rate distribution. So 1‐min cumulative distribution to every gauge station is derived from the piecewise regression results of Gamma distribution through half‐empirical conversion coefficients. We suggest the following actions: (1) In south China, there should be an approximately 9°E×5°N area of rain climatic zone K centered at about 112°E, 26°N inside International Telecommunication Union(ITU)‐R designed zone M. (2) A geostationary communication satellite for China should be placed over eastern China (between 100°E and 125°E) in order to generally reduce the rain attenuation of Earth‐satellite links all over China, based on rain rate distributions characteristic of China. Our data treatment procedure and results presented in this paper may be practical and useful in engineering design.

Comparison of the design of a contoured-beam and an elliptical-beam satellite offset reflector antennas to cover the Taiwan island region for satellite communications

For the design of the satellite antenna for the future geostationary (GEO) satellite communication or DBS (direct broadcasting satellite) applications to serve the Taiwan Island region, it may be required to have a antenna beam which effectively covers the Taiwan region and reduces the antenna radiation level in the nearby area of mainland China. Two cases of the Ka-band (20 GHz) satellite antenna, a shaped offset reflector antenna to synthesize a contoured beam and an elliptical offset reflector antenna to generate an elliptical beam, have been studied. This paper presents the comparison and discussion of the antenna coverage performance of the two designs.

A smallsát approach to large missions

The paper reviews potential Earth observation applications of small satellites using the LEOSTAR platform under development at Matra Marconi Space. This platform is able to support both optical and radar missions thanks to its relatively large payload capability (up to 500 kg) in the small satellite class. This allows users to consider payloads in a large variety of masses for experimental or operational missions, which can be grouped in payload complements coherent for achieving complex missions. The platform is proposed on a generic basis and can be customized to match new Earth observation mission requirements, in a way similar to the buses used for geostationary communication satellites. The costs in each satellite class are reduced as the platforms become a nearly recurrent part, thus making space affordable to a wider community. After a description of the capabilities of the LEOSTAR platform, the paper illustrates a number of planned Earth observation missions which will use it. The description of the missions includes that of the instrumentation and of the end application.

Spacecraft telemetry link performance in a transfer orbit

There are several critical periods early in the mission of a geo-stationary communication satellite. The first is the period from launch vehicle ignition until the upper stage final successful burn. The second is after the above span until the vehicle reaches its final altitude of a synchronous orbit. For a nominal low thrust apogee boost ascent subsystem during that later time, almost continuous telemetry is mandatory. This is especially true during the crucial periods of main engine burns and attitude correction phases. Maintaining a strong telemetry link throughout this phase requires an adequate RF signal link from the spacecraft to a ground station in the telemetry RF channel. An analysis of this link performance during each orbit until final position has two major aspects. One, the location of the spacecraft in relation to the ground tracking station at each moment in the mission is a matter of geometry and Keplerian physics. The other is the RF signal and its supporting subsystems, both on the ground and aboard the vehicle. The fundamental theoretical considerations or both the orbit parameters and radio link components are examined and then the individual parameter sensitivities are analyzed. Next, a nominal cast for a generic mission is studied. This survey considers the telemetry performance during each major stage of the flight from the launch through the transfer orbit to the postinjection period to the final orbit. Then abnormal situations due to both orbit and RF faults are examined. Finally, some design and operation concepts which may lessen the impact of the previous anomalies, are presented.

Design and Development of an Advanced Real-Time Satellite Simulator

An advanced real-time satellite simulator (ARTSS) has been developed to support the ground operations activities of the ETRI satellite control system, such as testing of the system facilities, validation of flight control procedures, verification of satellite commands as well as training of the ground operators. The design of ARTSS is based on the top-down approach and makes use of a modular programming to ensure flexibility in modification and expansion of the system. Graphics-based monitoring and control facilities enhance the satellite simulation environment. The software spacecraft model in ARTSS simulates the characteristics of a geostationary communication satellite using a momentum bias three-axis stabilization control technique. The system can be also interfaced with a hardware payload subsystem such as Ku-band communication transponder to enhance the simulator capability. Therefore, ARTSS is a high fidelity satellite simulation tool that can be used on low-cost desk top computers. In this paper, we describe the design features, the simulation models and the real-time operating functions of the simulator.

Analysis and design of a Ka‐band satellite shaped offset reflector antenna for producing a contoured beam to cover the Taiwan region

Abstract Analysis and design of a Ka‐band (20‐GHz) satellite offset‐fed shaped reflector antenna with a single feed for producing a contoured beam to cover the Taiwan region is presented. The design of this shaped reflector antenna is for future geostationary (GEO) satellite communication or DBS (direct broadcasting satellite) applications to serve the Taiwan region. The geometrical optics (GO)/aperture field (AF) method and aperture phase optimization procedures are employed for reflector surface shaping to produce the desired contoured beam. The physical optics (PO) method is used to accurately calculate the far‐field radiation pattern. Numerical simulation results show that the designed shaped reflector produces a Taiwan region converge beam and effectively reduces the antenna gain level in the nearby area of mainland China. Further reduction of the antenna gain level can be achieved by shifting the boresight direction of the satellite antenna for a certain small angle.

Comparison of Real-Time Ionospheric Algorithms for a GPS Wide-Area Augmentation System (WAAS)*

The Federal Aviation Administration (FAA) Satellite Program Office is developing a GPS Wide-Area Augmentation System (WAAS) to support a precision approach capability down to or near the lowest Category I (CAT I) decision height (DH) of 200 ft. In one of the candidate architectures under development, a vector of corrections is sent to the user via geostationary communications satellites (e.g., Inmarsat). This correction vector includes components for ionospheric, clock, and ephemeris corrections. The purpose of this paper is to evaluate the performance of the grid-based algorithms and other real-time ionospheric algorithms that could be implemented at the ground ionospheric reference stations, as well as at the airborne receiver. Results show that all of the ionospheric algorithms used in this paper (grid-based, least-squares, and spherical harmonics) provide roughly equivalent performance. Based on an extensive data collection program, the error in estimating ionospheric delay is derived. An analysis of WAAS accuracy performance is also presented.