Thesis (M.S.)--Ohio University, August, 2004. / Includes bibliographical references (p. 69-71)

Thesis (M.S.)--Ohio University, August, 2004. / Title from PDF t.p. Includes bibliographical references (p. 69-71)

Effectiveness of solar radiation pressure in the three-axis attitude control of present day and next generation of large communications satellites is investigated. A simple two-flap configuration is used with optimization of the direction of the applied control moment rather than the magnitude of the weak solar radiation pressure. Simulations were carried out in the presence of varying orbital eccentricity and inclination, solar aspect angle and controller dynamics parameters. Time histories of librational response against orbital position are presented for controlled and uncontrolled conditions. The results suggest the semipassive controller to be quite effective over a wide range of system parameters and it can meet the exacting pointing accuracy demanded by large communications satellites. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Doppler tracking of the Navy Navigation Satellite System (NNSS) gives solutions for polar motion as a by-product of the orbital computation process. The polar motion estimation process at the Defense Mapping Agency is reviewed and comparisons of the Doppler results with the polar motion series of the newer techniques, Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI), and the Bureau International de l'Heure (BIR) Circular-Dare made. TwoChandler periods of data are analyzed beginning with the start of the Main MERIT Campaign in September 1983. The two major components, annual and Chandler wobble, are removed. The resulting residuals, as well as those obtained by differencing all combinations of Doppler series and the three reference series, are smoothed by different techniques. The 'seven-point moving average' and the Vondrak smoothing algorithm are the two smoothers applied. A computational spectral analysis is presented that determines which periods dominate the residuals. / M.S.

No description available.

GPS has become very popular in recent years. It is used in wide range of applications including aircraft navigation, search and rescue, space borne attitude and position determination and cellular network synchronization. Each application places demands on GPS for various levels of accuracy, integrity, system availability and continuity of service. Radio frequency interference (RFI) which results from many sources such as TV/FM harmonics, radar or mobile satellite systems, presents a challenge to the use of GPS. It can affect all the service performance indices mentioned above. To improve the accuracy of GPS positioning, a continuously operating reference station (CORS) network can be used. A CORS network provides all the enabled GPS users in an area with corrections to the fundamental measurements, producing more precise positioning. A threat to these networks is a threat to all high-accuracy GPS users. It is therefore necessary to monitor the quality of the received signal with the objective of promptly detecting the presence of RFI and providing a timely warning of the degradation of system accuracy, thereby boosting the integrity of GPS. This research was focused on four main tasks: a) Detection. The focus here is on a power spectral density fluctuation detection technique, in which statistical inference is used to detect narrowband continuous-wave (CW) interference in the GPS signal band after being captured by the RF front-end. An optimal detector algorithm is proposed. At this optimal point, for a fixed Detection Threshold (DT), probability of false alarm becomes minimal and for a fixed probability of false alarm, we can achieve the minimum value for the detection threshold. Experiments show that at this point we have the minimum computational load. This theoretical result is supported by real experiments. Finally this algorithm is employed to detect a real GPS interference signal generated by a TV transmitter in Sydney. b) Characterization. In the characterization section, using the GNSS signal structure and the baseband signal processing inside the GNSS receiver, a closed formula is derived for the received signal quality in terms of effective carrier to noise ratio ( ). This formula is tested and proved by calculating the C/No using the I and Q data from a software GPS receiver. For pulsed CW, a similar analysis is done to characterize the effect of parameters such as pulse repetition period (PRP) and also duty cycle on the received signal quality. Considering this characterization and the commonality between the GPS C/A code and Galileo signal as a basis to build up a common term for satellite availability, the probability of satellite availability in the presence of CW interference is defined and for the two currently available satellite navigation systems (GPS L1 signal and Galileo signal (GIOVE-A BOC(1, 1) in the E1/L1 band)) it is shown that they can be considered as alternatives to each other in the presence of different RFI frequencies as their availability in the presence of CW RFI is different in terms of RFI frequency. c) Mitigation. The last section of the research presents a new concept of ?Satellite Exclusion Zone?. In this technique, using our previously developed characterization techniques, and considering the fact that RFI has different effects on different satellite signals at different times depending on satellite Doppler frequency, the idea of excluding the most vulnerable satellite signal from positioning calculations is proposed. Using real data and real interference, the effectiveness of this technique is proven and its performance analyzed. d) Hardware implementation. The above detection technique is implemented using the UNSW FPGA receiver board called NAMURU.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 19, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. C. Mark Cowell. Includes bibliographical references.

In the next coming years global satellite navigation systems (GNSS) will make part of our daily life, as the world is becoming "GNSS-dependant in the same way that it has become Internet-dependant". Indeed, more than ten years folowing the opening up to civilians of satellite-based navigation systems initially designed for military purposes, civil satellite navigation applications are becoming more and more numerous. The potential benefits have proven enormous in terms of transport safety and efficiency as well as for non-transport-related industries. / Dans les toutes prochaines années, les systèmes globaux de navigation par satellite (GNSS) feront partie intégrante de notre vie quotidienne. En effet, un peu plus de dix ans après la libéralisation de l'accès des civils aux systèmes de navigation par satellite initialement conçus à des fins militaires, les applications civiles permises par la navigation par satellite sont de plus en plus nombreuses et les bénéfices potentiels sont énormes en matière de sécurité et d'efficacité des transports comme pour d'autres secteurs et industries. fr

Deregulation, globalization, and commercialization are drastically changing the space industry. But commercial space activities entail considerable risks. This thesis is primarily an analysis of the risks that private entities in the space industry need to manage in order to be commercially successful. Due to the trend towards a buyer's market, satellite manufacturers increasingly have been forced to accept risks that do not fall within their traditional core business. Consequently, manufacturing companies become risk managers for a variety of legal space risks. Therefore, the legal framework for the commercial management of legal risks is analyzed and solutions to identified problems are offered. This thesis studies trends in contemporary risk management practices in the private sector, which is dominated by market forces. It is argued that risk management of legal issues should form an integral part of overall space project management, the rationale being that losses in any phase of space activities, while certain to occur, are uncertain in time and scale. This thesis, therefore, scrutinizes legal risk management throughout the life cycle of space projects. Few space applications have become commercially viable. Today, satellite navigation provided by the U.S. GPS is widely used, especially because it is free of direct charges. In Europe, a competing system, Galileo, is being developed. It will provide users with different service levels, ranging from free services to more reliable and accurate navigation services. As this system has both, public and commercial benefits, the industry is expected to participate in a Public Private Partnership for the Galileo satellite constellation. This thesis makes specific proposals to manage the legal risks of the Galileo project. At the same time, the allocation of legal space risks between the various parties is studied. The thesis of the author is that the management process, which is used to control technical space risks, can provide satellite manufacturers with a supportive analogy for dealing with legal space risks. Risks will be studied for all project phases of Galileo, i.e., the feasibility study, the establishment of specifications, development, manufacturing, the launch, operations, replenishment, and the final disposition of satellites.

Three studies of precipitable water using the Global Positioning System are presented. The first study finds that precipitable water in Hawaiʻi is best described by a lognormal distribution. The long-term average value of precipitable water declines exponentially with height, but the dispersion of precipitable water declines more linearly. The change in skewness of the distributions is also linear, although in this case it increases with elevation. The second and third studies use GPS meteorology to investigate a climatological and a meteorological event respectively. First, the effect of the 1997-1998 El Nino on precipitable water in the western tropical Pacific is studied and found to be consistent with a model relating the formation of an anomalous high-pressure ridge to the El Nino episode. Finally, the details of the precipitable water field for the Kaʻu Storm, November 2000 are examined. The results highlight the role of topography in controlling the location of convection, The observed correlation between the precipitable water and rainfall is used to generate estimates of rainfall based on GPS data, Comparing the GPS precipitable water estimates with those from a weather model indicates that the underestimates of rainfall produced by the weather model are probably due to correlated underestimates of precipitable water. / Thesis (Ph. D.)--University of Hawaii at Manoa, 2002. / Mode of access: World Wide Web. / Includes bibliographical references (leaves 62-66). / Electronic reproduction. / Also available by subscription via World Wide Web / ix, 66 leaves, bound ill. 29 cm