Geostationary Communication Research Articles

SCoBi-Veg: A Generalized Bistatic Scattering Model of Reflectometry From Vegetation for Signals of Opportunity Applications

SCoBi-Veg stands for Signals of opportunity Coherent Bistatic scattering model for Vegetated terrains. It simulates polarimetric reflectometry of vegetation canopy over a flat ground using a Monte Carlo scheme. The model is aimed at assessing the value of navigation and communication satellite Signals of Opportunity in a range of frequencies from P- to S-bands for remote sensing of a number of geophysical land parameters such as soil moisture and biomass. A fully polarimetric expression for bistatic scattering from a vegetation canopy is first formulated for a general case and is then specialized to the practical case of ground-based/low-altitude platforms with passive receivers overlooking vegetation using the signals transmitted from large distances. Using analytical wave theory in conjunction with distorted Born approximation, the transmit and receive antenna effects (i.e., polarization crosstalk/mismatch, orientation, and altitude) are explicitly accounted for. The forward model developed here enables the understanding of the effect of different geophysical parameters and system configurations on the coherent and incoherent components of the reflected signatures. It can thus help developing robust inverse algorithm for extraction of soil moisture and biomass. The model is applied to P-band signals of geostationary communication satellites to describe polarimetric reflections from tree canopies as observed from down-looking platforms at various altitudes. The relative contributions of diffuse and specular scattering on total reflected power and reflectivity are quantified for various observing scenarios.

Spatial distribution of soil moisture estimates using a multiple linear regression model and Korean geostationary satellite (COMS) data

This study attempts to estimate the spatial distribution of the soil moisture (SM) in South Korea (99,260 km2) from January 2013 to May 2015 using a multiple linear regression (MLR) model with data from the Korean multipurpose geostationary Communication, Ocean and Meteorological Satellite (COMS), and land surface temperature (LST) data. The normalized distribution vegetation index (NDVI) from the moderate-resolution imaging spectroradiometer (MODIS) on board the Terra satellite was used to reflect the vegetation variations. Observed precipitation data measured by automatic weather stations (AWSs) operated by the Korea Meteorological Administration (KMA) were collected, and SM data were collected from 38 stations operated by various institutions. The regression coefficients of the MLR model were estimated seasonally considering five days of preceding precipitation. The p-values of all regression coefficients were below 0.05, and all coefficients of determination (R2) ranged from 0.17 to 0.63. Specifically, the R2 of loam in the summer was the highest at 0.63, and most of the R2 values were 0.4 or higher. The results of the SM regression showed that the overall R2 was higher than 0.4 and that the root mean square error (RMSE) was less than 5% at all but a few stations. A time series analysis of the simulated SM revealed that the observed SM data ranged from 0 to 20% for sand, 10 to 30% for loam, 20 to 40% for clay and 30 to 50% for silt. The simulated SM followed the volatility of the observed data in most of the soils. The spatial distribution of the simulated SM showed the same trends with the observed data on the monthly spatial precipitation map. Consequently, the estimated map of the soil moisture index (SMI) can be used to better understand the severity of drought and the variability in the SM.

Establishing a framework to explore the Servicer-Client relationship in On-Orbit Servicing

On-Orbit Servicing (OOS) is becoming more extensively discussed in research and commercial developments. The key point of servicing relies on the relation between two systems, the Servicer executing the tasks and the Client being serviced. With the increase of interest in OOS applications, the exploration of the Client-Servicer relationship in different scenarios becomes a necessary step in servicing implementation. Exploring such a relationship involves translating the information available about OOS into useful inputs for spacecraft design, a challenging task due to the variety of applications and possible interactions between both sides. Then, different modelling and simulation techniques can be used to model and to explore the interaction of such complex systems for different scenarios of servicing. This paper presents an agent-based framework to explore the relations of Servicer and Client for applications of On-Orbit Servicing. To do so, the case for a hypothetical satellite operator is explored, under a specific set of requirements and conditions for different servicing solutions. First, the Agent Based Modelling and Simulation (ABMS) is established based on a specific set of rules, definition metrics and operation characteristics relating Servicer and Client. Then, the basic assumptions of Client, Servicer and servicing operations are discussed and the initial simulation parameters are defined. The ABMS is used to simulate OOS for a fleet of geostationary communication satellites for the cases of Lifetime Extension, Refuel and Rescue and Recover. In the end, the ABMS outputs are used to explore the design aspects of the Servicer and Client satellites at systems level. The results highlight the advantages of having this type of framework for early assessment of OOS under different types of context for both Servicer and Client. The paper concludes with directions of how the framework can be used to explore more complex and realistic scenarios of OOS, and assess their potential benefits.

Bacon’s New Atlantis and the Fictional Origins of Organised Science

Abstract It is a commonplace that science fiction draws inspiration from science fact. It is a less familiar thought-though still widely acknowledged-that science has sometimes drawn its inspiration from science fiction. (Arthur C. Clarke’s idea of geostationary communications satellites is a well-known example.) However, the debt of science to science fiction extends beyond such specific examples of scientific and technological innovations. This essay explores the paradoxical-sounding thesis that science itself, as we now know it, was originally the product of a science fiction vision. At a time when the collective endeavours of early modern researchers amounted to something less than science, Francis Bacon’s New Atlantis (1627) helped show what wonders might be achieved by organised and methodical state-sponsored scientific research. Bacon’s vision was highly prescient: many of the scientific possibilities he sketched have since become realities. It was also highly influential: early modern science bears the characteristic stamp of Bacon’s vision, and that same influence is discernible right down to the present day.

A Novel Location-Awareness Method Using CubeSats for Locating the Spot Beam Emitters of Geostationary Communications Satellites

As more spacecraft are launched into the Geostationary Earth Orbit (GEO) belt, the possibility of fatal collisions or unnecessary interference between spacecraft increases. In this paper, a new location-awareness method that uses CubeSats is proposed to assist with radiofrequency (RF) domain verification by means of awareness and identification of the positions of the spot beam emitters of communications satellites in geostationary orbit. By flying a CubeSat (or a constellation of CubeSats) through the coverage area of a spot beam, the spot beam emitter’s position is identified and the spot beam’s pattern knowledge is characterized. The geometry, the equations of motion of the spacecraft, the measurement process, and the filtering equations in a location system are addressed with respect to the location methods investigated in this study. A realistic scenario in which a CubeSat receives signals from GEO communications satellites is simulated using the Systems Tool Kit (STK). The results of the simulation and the analysis presented in this study provide a thorough verification of the performance of the location-awareness method.

Solar array degradation on geostationary communications satellites: the quantification of annual degradation and degradation over solar proton events

Solar array degradation on geostationary communications satellites: the quantification of annual degradation and degradation over solar proton events

Solar array degradation on geostationary communications satellites: the quantification of annual degradation and degradation over solar proton events

Solar array telemetry from eleven geostationary communication satellites, launched between 1990 and 1998, was analysed and used to quantify solar array degradation of gallium arsenide (GaAs) and silicon (Si) solar cells. GaAs cells had an average annual percent degradation ranging between 0.44% and 1.03%, while Si cells had an average annual percent degradation ranging between 0.71% and 1.69%. The decrease in Si cells degradation rates, based on telemetry of Isc and Voc levels, ~1,210% over a ten years mission suggests an update to the Si solar cell degradation design rule of thumb 25% over a ten year mission. Degradation during solar particle events (SPEs) of 10 MeV proton flux > 10,000 pfu was analysed and used to create an initial functional relationship between degradation experienced over SPEs and the accumulated fluence of these SPEs.

Surface albedo from the geostationary Communication, Ocean and Meteorological Satellite (COMS)/Meteorological Imager (MI) observation system

The surface albedo is an essential climate variable that is considered in many applications used for predicting climate and understanding the mechanisms of climate change. In this study, surface albedo was estimated using a bidirectional reflectance distribution function model based on Communication, Ocean and Meteorological Satellite/Meteorological Imager data. Geostationary orbiting satellite data are suitable for a level 2 product like albedo, which requires a synthetic process to estimate. The authors modified established methods to consider the geometry of the solar-surface-sensor of COMS/MI. Of note, the viewing zenith angle term was removed from the kernel integration used for estimating spectral albedo. Finally, the spectral (narrow) albedo was converted into the broadband albedo with shortwave length (approximately 0.3–2.5 μm). This study determined conversion coefficients using only one spectral albedo of visible channel. The estimated albedo had a relatively high correlation with Satellite Pour l’Observation de la Terre/Vegetation and low unweighted error values specific for land types or times. The validation results show that estimated albedo has a root mean square error of 0.0134 at Jeju flux site that indicates accuracy similar to that of other satellite-based products.

Quantifying the inflation factors of observation error variance for COMS and MTSAT Atmospheric Motion Vectors considering spatial observation error correlation

In this study, the spatial error correlations in the Atmospheric Motion Vectors (AMVs) derived from the geostationary satellite imagery over East Asia are investigated. Good characterization of systematic errors in observations is essential in order to extract the maximum amount of information from the observations during the assimilation process. The spatial structure of AMV error correlations was identified based on datasets of AMVs collocated with sonde observations for July 2015. Results of AMVs from water vapour (WV; 6.7 µm) and infrared (IR; 10.8 µm) channels of the Korean geostationary Communication, Ocean and Meteorological Satellite (COMS) and the Multifunction Transport Satellite‐2 (MTSAT) are presented. For both channels, the length scales of the spatial error correlations in the MTSAT AMVs are longer than those of the COMS AMVs. For MTSAT (COMS) AMVs, a longer (shorter) length‐scale yields more (less) inflated observation error variance, and a larger (smaller) inflation factor for the diagonal form of the observation error covariance matrix is required to obtain the best quality of analysis.

The Rise of the Electric Age for Satellite Propulsion

Abstract A prediction of future directions and trends of the satellite propulsion market could be helpful in the formation of technology development agendas proposed by various global entities such as commercial companies, space agencies, or research institutions. Possible market evolutions are presented, in light of past and present technology development, and the authors' estimation of the upcoming development tracks of the various forms and subclasses of electric propulsion (EP). The history of EP is reviewed in the context of a technology life cycle, with the conclusion that EP is in its early majority pragmatist phase. Specific applications for in-space propulsion, including geostationary communication satellites, low Earth orbit mega constellations, CubeSats, interplanetary missions, and Earth observation satellites, are paired with the appropriate corresponding EP technologies. Rising developers and major influences are noted. It is predicted that EP technologies will likely fragment and diversify ...

Response of geostationary communications satellite solid-state power amplifiers to high-energy electron fluence

Air Force Office of Sponsored Research (AFOSR) grant FA9550-13-1-0099 and the National Science Foundation (NSF)

Autonomous star sensor ASTRO APS: flight experience on Alphasat

Jena-Optronik GmbH, located in Jena/Germany, has profound experience in designing and manufacturing star trackers since the early 80s. Today the company has a worldwide leading position in supplying geo-stationary and Earth observation satellites with robust and reliable star tracker systems. In the first decade of the new century Jena-Optronik received a development contract (17317/2003/F/WE) from the European Space Agency to establish the technologically challenging elements for which advanced star tracker technologies as CMOS Active Pixel Sensors were being introduced or were considered strategic. This activity was performed in the frame of the Alphabus large platform pre-development lead by ESA and the industrial Joint Project Team consisting of Astrium (now Airbus Defence and Space), Thales Alenia Space and CNES (Centre national d’etudes spatiales). The new autonomous star tracker, ASTRO APS (Active Pixel Sensor), extends the Jena-Optronik Astro-series CCD-based star tracker products taken the full benefit of the CMOS APS technology. ASTRO APS is a fully autonomous compact star tracker carrying either the space-qualified radiation hard STAR1000 or the HAS2 APS detectors. The star tracker is one of four Technology Demonstration Payloads (TDP6) carried by Alphasat as hosted payload in the frame of a successful Private Public Partnership between ESA and Inmarsat who owns and operates the satellite as part of its geo-stationary communication satellites fleet. TDP6 supports also directly TDP1, a Laser Communication Terminal, for fine pointing tasks. Alphasat was flawlessly brought in orbit at the end of July 2013 by a European Ariane 5 launcher. Only a few hours after launch the star tracker received its switch ON command and acquired nominally within 6 s the inertial 3-axes attitude. In the following days of the early in-orbit operations of Alphasat the TDP6 unit tracked reliably all the spacecraft maneuvers including the 0.1 and 0.2°/s spin stabilization for Sun pointing, all of the apogee engine thrusts, Moon field of view transits and recovered to stable tracking after several Earth and Sun blindings before the spacecraft entered a preliminary Earth pointing in a nominal geo-stationary attitude. The Jena-Optronik TDP6 operation center received daily the star tracker status and attitude data. The huge amount of acquired raw data has been evaluated to characterize the ASTRO APS (STAR1000) star tracker in-orbit performance. The paper will present in detail these data processing activities and will show the extraordinary good results. Due to the diverse transfer orbit satellite operations the key performance star tracker data like attitude random noise, single star noise, star brightness measurement, baffle Sun exclusion angle, temperature control, etc., could be derived and have been compared to the ground based laboratory and field measurements. The ultimate performance parameters achieved and verified as well as the lessons learned from the comparison to the ground test data are summarized in the conclusion of the paper.

GaAs MMIC를 이용한 X대역용 25W급 전력증폭모듈의 설계 및 구현에 대한 연구

To be used in a transmitter of a satellite transponder of this paper, X band 25W power amplifier module, a part constituting of high-power amplifier is transmitted to the equipment for transmitting to geostationary communications satellites(36,000Km distance). PAM consisted a total of four power amplifier module has a high output characteristic of the high-output amplifier is used in the ground station. Used in conjunction with the structured type power amplifier module is composed of Serial Combining Structure. This PAM(Power Amplifier Module) configured by combining the circuit with the power amplifier, 10 MMIC chips and the Al2O3 thin film substrate using a Hybrid Technique of power amplifier module, was implemented at X band PAM(Power Amplifier Module) of 25W grade.

The Impact of Radio-Frequency Interference on WindSat Ocean Surface Observations

To study the effects of radio-frequency interference (RFI) on remote sensing data, we examined five years of WindSat ocean observations from regions affected by reflected X-band emissions from geostationary communication satellites. We compared measured brightness temperatures to modeled brightness temperatures obtained using mitigated retrievals as input to the WindSat parameterized radiative transfer model, demonstrating a considerable contribution to the radiometric measurements from interference. Comparisons of potentially contaminated retrievals of sea surface temperature (SST), wind speed, and wind direction with surface reanalyses confirmed that the presence of RFI can bias retrievals while also increasing retrieval uncertainty. Mitigation removed most of the biases. The quality of mitigated SST and wind speed retrievals was comparable to uncontaminated retrievals; however, the performance of first-rank wind directions was noticeably degraded. Recommendations are given on the use of contaminated and mitigated data, from radiance assimilation to climate studies.

Evaluation of Land Surface Temperature Operationally Retrieved from Korean Geostationary Satellite (COMS) Data

We evaluated the precision of land surface temperature (LST) operationally retrieved from the Korean multipurpose geostationary satellite, Communication, Ocean and Meteorological Satellite (COMS). The split-window (SW)-type retrieval algorithm was developed through radiative transfer model simulations under various atmospheric profiles, satellite zenith angles, surface emissivity values and surface lapse rate conditions using Moderate Resolution Atmospheric Transmission version 4 (MODTRAN4). The estimation capabilities of the COMS SW (CSW) LST algorithm were evaluated for various impacting factors, and the retrieval accuracy of COMS LST data was evaluated with collocated Moderate Resolution Imaging Spectroradiometer (MODIS) LST data. The surface emissivity values for two SW channels were generated using a vegetation cover method. The CSW algorithm estimated the LST distribution reasonably well (averaged bias = 0.00 K, Root Mean Square Error (RMSE) = 1.41 K, correlation coefficient = 0.99); however, the estimation capabilities of the CSW algorithm were significantly impacted by large brightness temperature differences and surface lapse rates. The CSW algorithm reproduced spatiotemporal variations of LST comparing well to MODIS LST data, irrespective of what month or time of day the data were collected from. The one-year evaluation results with MODIS LST data showed that the annual mean bias, RMSE and correlation coefficient for the CSW algorithm were −1.009 K, 2.613 K and 0.988, respectively.

Space weather radiation effects on geostationary satellite solid‐state power amplifiers

AbstractIn order to understand and mitigate the effects of space weather on the performance of geostationary (GEO) communications satellites, we analyze 16 years of archived telemetry data from Inmarsat, the UK‐based telecommunications company. We compare 665,112 operational hours of housekeeping telemetry from two generations of satellites, designated as Fleet A and Fleet B. Each generation experienced 13 solid‐state power amplifier (SSPA) anomalies for a total of 26 anomalies from 1996 to 2012. We compare telemetry from the Inmarsat anomalies with space weather observations, including data from the OMNI2 database, Geostationary Operational Environmental Satellites, the Advanced Composition Explorer Satellite, and Los Alamos National Laboratory (LANL) GEO observations; the evolution of the sunspot number; and the Kp index. Most SSPA anomalies for Fleet A occur as solar activity declines; Fleet B has not yet experienced a full solar cycle. For both fleets, the average value of Kp remained < 2 over time periods of 2 days, 3 days, and 2 weeks around the time of anomaly, which suggests that the anomalies occurred at times of relatively quiet geomagnetic activity and that they were probably not solely caused by surface charging. From 1996 to 2009, the average of the 1.8–3.5 MeV electron flux was 1.98 #/(cm2 s st keV). Five of the 26 anomalies, unfortunately, do not have corresponding science observations (specifically, electron flux data in the LANL data set), so part of this study focuses on the 21 anomalies when science observations were available. Six out of 21 anomalies experienced a high‐energy electron flux greater than 1.5 standard deviations above the mean of the log10 of the flux between 7 and 14 days prior to the anomaly. By contrast, a Monte Carlo simulation finds that on average, only 2.8 out of 21 (13%) of randomly assigned “anomalies” occur between 7 and 14 days after an electron flux greater than 1.5 standard deviations above the mean. Our observations suggest that internal charging from either past elevated radiation belt fluxes or some conditions related to relativistic electron enhancements (either causally or accidentally) is most likely responsible for the SSPA anomalies. We next consider the timing of these anomalies with respect to the local time (LT) and season. Anomalies occur at all LT sectors with 46% (Fleet A) and 38.5% (Fleet B) in the midnight to dawn sector and 54% (Fleet A) and 46% (Fleet B) in the local noon to dusk sector. From the local time distribution, surface charging does not appear to be the sole causative agent of the anomalies. Understanding the connection between the space weather conditions and anomalies on subsystems and specific components on identical and similar geostationary communications satellites for periods of time longer than a solar cycle will help guide design improvements and provide insight on their operation during space weather events.

Feasibility Study of a Vega Launched Geostationary Communication Satellite

This paper covers an analysis on the use of a hybrid propulsion system for the Low Earth Orbits to Geostationary Orbit transfer, while addressing issues related to the environment encountered during the orbit raising. This feasibility study is based on the proposal [1] by La Sapienza for a compact and efficient telecommunications satellite, compatible with a launch of the Vega space transport system and characterized by the use of electric propulsion for the orbital transfer. The idea of a Vega compatible telecommunications satellite mission falls within the lines of re-launch of satellite telecommunications programs by the Italian Space Agency with missions already under development and with a view to enhance and strengthen the domestic industry and the systemic capabilities already pride of the country. In addition, the synergy with the Vega launcher, and its potential developments, encourage developments of great interest for the role of Europe in the launch activities, extending its potentials.

High-Resolution Operational Coastal Modeling System for the Prediction of Hydrodynamics in Korea Using a Wave-Current Coupled Model

Lim, H.S., Chun, I.S., Kim, C.S., Park, K.S., Shim, J.S. and Yoon, J.J, 2013. High-Resolution Operational Coastal Modeling System for the Prediction of Hydrodynamics in Korea Using a Wave-Current Coupled ModelWe have developed a high-resolution operational coastal modeling system for the coastal waters of Korea using a wave-current coupled model ROMS. The operational oceanographic system consists of operational modeling and monitoring modules. The modeling system comprises atmospheric and hydrodynamic models coupled with three-dimensional hydrodynamics, wave, sediment transport, and water quality model. The hydrodynamic variables are forecasted on a 72-hour basis. The real-time monitoring system is comprised of buoy, HF-radar and geostationary Communication Ocean Meteorological Satellite (COMS). The web-GIS-based coastal information system provides predicted results with real-time monitoring data for dissemination to the public and validation of the predicted results. The operational coastal modeling system uses the ROMS hydrodynamic model coupled with SWAN, a wave model. WRF is used for meteorological modeling of atmospheric forcing, NAO.99jb is a regional tide model used for the tides, and CE-QUAL-ICM is an eutrophication model that is used for simulating the water quality. The atmospheric forcing is derived from the predicted results of the WRF atmospheric model, which has been operated for forecasting in the East China Sea and East Sea. The ocean boundary condition is derived from data-assimilative ROMS, which has been in operation for the Yellow Sea. The hydrodynamic variables were calibrated with tidal surface elevation and verified with current data observed by a bottom-mounted ADCP and AWAC. To validate the predicted results, we use real-time monitoring data from hydrodynamic measurements observed by the operational AWAC and buoy, 1-h averaged surface currents measured by HF-radar, and suspended sediment concentration (SSC) obtained hourly and derived from the Geostationary Ocean Color Imager (GOCI) of COMS. The wave-current coupled ROMS-SWAN modeling system shows enhanced wave-current interaction for the coastal waters of Korea, especially for the prediction of storm surge height and variation of suspended sediment transport. This operational coastal modeling system has been originally developed for the prediction system of coastal waters of Korea and used for the development of an Integrated-Maritime Prediction System (I-MAPS) supporting the operation of the major ports system of Korea such as Incheon and Gunsan on the western coast of Korea, and Yeosu, Masan and Busan on the southern coast of Korea. I-MAPS will also provide monitoring and predicted data to governmental agencies and to the public to support ship navigation and marine activity and to solve problems associated with coastal accidents, such as storm surge, inundation, search and rescue, and oil-spills, as a part of the Korea Operational Oceanographic System (KOOS) which will be in operation by the end of 2013.

Communication-based positioning systems: past, present and prospects

This paper reviews positioning systems in the context of communication systems. First, the basic positioning technique is described for location based service (LBS) in mobile communication systems. Then the high integrity global positioning system (iGPS) is introduced in terms of aspects of what it is and how the low Earth orbit (LEO) Iridium telecommunication satellites enhance the global positioning system (GPS). Emphasis is on the Chinese Area Positioning System (CAPS) which is mainly based on commercial geostationary (GEO) communication satellites, including decommissioned GEO and inclined geosynchronous communication satellites. Characterized by its low cost, high flexibility, wide-area coverage and ample frequency resources, a distinctive feature of CAPS is that its navigation messages are generated on the ground, then uploaded to and forwarded by the communication satellites. Fundamental principles and key technologies applied in the construction of CAPS are presented in detail from the CAPS validation phase to its experimental system setup. A prospective view of CAPS has concluded it to be a seamless, high accuracy, large capacity navigation and communication system which can be achieved by expanding it world wide and enhancing it with LEO satellites and mobile base stations. Hence, this system is a potential candidate for the next generation of radio navigation after GPS.

Анализ перспектив расширения функциональных возможностей украинского геостационарного спутника связи

Анализ перспектив расширения функциональных возможностей украинского геостационарного спутника связи