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Satellite technology represents the only technique for measuring sea surface temperatures (SSTs) on a global scale. SSTs are important as boundary conditions for climate and atmospheric boundary layer models which attempt to describe phenomena of all scales, ranging from local forecasts to predictions of global warming. Historical use of infrared satellite measurements for SST determination has been based on a theory which assumes that the atmosphere is 'thin', i.e., that atmospheric absorption of infrared radiation emitted from the sea surface has very little effect on the radiant intensity that is measured by satellites. However, a variety of independent radiative transfer models point to the possibility that the so-called 'thin approximation' is violated for humid atmospheres such as those found in the tropics, leading to errors in the retrieved SST that would be unacceptable to those who make use of such products. Furthermore, such tropical regions represent a significant portion of the globe, where coupled ocean-atmosphere disturbances can have global effects (e.g., the tropical Pacific El Nino-Southern Oscillation events). This study evaluates the thin approximation empirically, by combining radiative transfer theory and satellite data from the Eastern Atlantic ocean region studied during the Atlantic Statocumulus Transition Experiment (ASTEX). Six months of satellite data from May, June, and July of 1983 and 1984 are analyzed. To the degree that the data may be considered representative of globally valid relationships between measured variables, it is shown that the thin approximation is not appropriate for the tropics. This suggests that new methods are necessary for retrieving SSTs from the more humid regions of the globe. / Graduation date: 1993

Dissertation (Ph. D.)--University of Stellenbosch, 1997. / Bibliography. Also available via the Internet

Nowadays, Global Positioning System (GPS) which provide global coverage, continuous tracking capability and high accuracy has been preferred as the primary tracking system for onboard real-time precision orbit determination of Low Earth Orbiters (LEO). In this work, real-time orbit determination algorithms are established on the basis of extended Kalman, unscented Kalman, regularized particle, extended Kalman particle and extended H-infinity filters. Particularly, particle filters which have not been applied to the real time orbit determination until now are also performed in this study and H-infinity filter is presented using all kinds of real GPS observations. Additionally, performance of unscented Kalman filter using GRAPHIC (Group and Phase Ionospheric Correction) measurements is investigated. To evaluate performances of all algorithms, comparisons are carried out using different types of GPS observations concerning C/A (Coarse/Acquisition) code pseudorange, GRAPHIC and navigation solutions. A software package for real time orbit determination is developed using recursive filters mentioned above. The software is implemented and tested in MATLAB&copy / R2010 programming language environment on the basis of the object oriented programming schema.

This thesis brings statistical analyses techniques to bear on data derived from an extensive database of satellite launches and on-orbit anomalies and failures. The data collected is analyzed from two different perspectives and addresses, in two separate studies, two research objectives. The first study proposes to identify trends and cyclical patterns in the space industry, and to forecast the volume of launches for the next few years. Satellites have been rightfully described as the lifeblood of the entire space industry and the number of satellites ordered or launched per year is an important defining metric of the industry's level of activity. The structure of the space industry, its financial health and its workforce retention and development is dependent on the volume of satellites contracted. As such, trends and variability in this volume have significant strategic impact on the space industry. Over the past 40+ years, hundreds of satellites have been launched every year. Thus, an important data set is available for time series analysis and identification of trends and cycles in the various markets of the space industry. For the purpose of this first study, we collected data for over 6,000 satellites launched since 1960 on a yearly basis. We separated the satellites into three broad segments: 1) defense and intelligence satellites, 2) science satellites, and 3) commercial satellites. Several techniques are available for the analysis of time series data, both in the time domain and in the frequency domain. In this first study, we conducted spectral analysis of the time series for each of the three satellite populations and identified cycles contained in the data. In addition, once harmonic models were derived and fitted to the data, we built forecasting models of satellite launch volumes in the different market segments for the next few years. The potential implications of the results are discussed as a number of strategic matters for the space industry are contingent on the predictions or forecast of the volume of satellites contracted (the example of the U.S. auto industry is a solemn reminder of such possible strategic issues). The second study uses the previously collected launch data, confined to Earth-orbiting satellites launched between 1990 and 2008, and expanded with the failure information and retirement of each satellite to conduct a comparative analysis of satellite reliability in GEO, LEO, and MEO orbits. Reliability has long been recognized as an essential consideration in the design of space systems. However, there is limited statistical analysis of satellite reliability based on actual flight data. The objective of this second study is to conduct nonparametric satellite reliability analysis, with orbit type as a covariate, and to explore appropriate parametric fits (Weibull, lognormal, and mixture distributions). The results indicate for example that differences exist between the failure behaviors of satellites in different orbits, or that satellite infant mortality exists or dominates more clearly in a particular orbit type. The findings can be useful to satellite manufacturers as they would provide an empirical basis for reviewing and adjusting satellite testing and burn-in procedures.

Future spacecraft missions are trending towards the use of distributed systems or fractionated spacecraft. Initiatives such as DARPA's System F6 are encouraging the satellite community to explore the realm of collaborative spacecraft teams in order to achieve lower cost, lower risk, and greater data value over the conventional monoliths in LEO today. Extensive research has been and is being conducted indicating the advantages of distributed spacecraft systems in terms of both capability and cost. Enabling collaborative behaviors among teams or formations of pico-satellites requires technology development in several subsystem areas including attitude determination and control subsystems, orbit determination and maintenance capabilities, as well as a means to maintain accurate knowledge of team members' position and attitude. All of these technology developments desire improvements (more specifically, decreases) in mass and power requirements in order to fit on pico-satellite platforms such as the CubeSat. In this thesis a solution for the last technology development area aforementioned is presented. Accurate knowledge of each spacecraft's state in a formation, beyond improving collision avoidance, provides a means to best schedule sensor data gathering, thereby increasing power budget efficiency. Our solution is composed of multiple software and hardware components. First, finely-tuned flight system software for the maintaining of state knowledge through equations of motion propagation is developed. Additional software, including an extended Kalman filter implementation, and commercially available hardware components provide a means for on-board determination of both orbit and attitude. Lastly, an inter-satellite communication message structure and protocol enable the updating of position and attitude, as required, among team members. This messaging structure additionally provides a means for payload sensor and telemetry data sharing. In order to satisfy the needs of many different missions, the software has the flexibility to vary the limits of accuracy on the knowledge of team member position, velocity, and attitude. Such flexibility provides power savings for simpler applications while still enabling missions with the need of finer accuracy knowledge of the distributed team's state. Simulation results are presented indicating the accuracy and efficiency of formation structure knowledge through incorporation of the described solution. More importantly, results indicate the collaborative module's ability to maintain formation knowledge within bounds prescribed by a user. Simulation has included hardware-in-the-loop setups utilizing an S-band transceiver. Two "satellites" (computers setup with S-band transceivers and running the software components of the collaborative module) are provided GPS inputs comparable to the outputs provided from commercial hardware; this partial hardware-in-the-loop setup demonstrates the overall capabilities of the collaborative module. Details on each component of the module are provided. Although the module is designed with the 3U CubeSat framework as the initial demonstration platform, it is easily extendable onto other small satellite platforms. By using this collaborative module as a base, future work can build upon it with attitude control, orbit or formation control, and additional capabilities with the end goal of achieving autonomous clusters of small spacecraft.

Tex., Univ. of Texas, Reports Master of Arts--Austin, 1982. / Die Vorlage enth. insgesamt 2 Werke. Includes bibliographical references. Vita.

Thesis (M.S. in Space Systems Operations)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Richard Olsen, Richard Harkins. Includes bibliographical references (p. 43). Also available online.

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.