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Systems are becoming increasingly more complex. To follow this increasingly complexity, systems engineering must evolve rapidly with the introduction of new methodologies, processes, tools, etc. Due to this rapid evolution, little attention is dedicated to the study of the history of its evolution. Currently there is the initiative of installation of a chapter of INCOSE (International Council on Systems Engineering) in Brazil and from this initiative emerged the interest of recovering the history of systems engineering in the country. There are indications that the introduction of systems engineering into Brazil occurred in the late 1960's, directly from NASA and that its first applications in Brazil were in Space Systems Engineering. This paper recovers the origins of systems engineering, of its introduction into Brazil, and of its use in space systems engineering.

Since its introduction at INPE, in the late 1960s, Systems Engineering has passed through phases of greater and lesser importance. Three different phases are clearly recognized. The first two phases are closely associated with efforts to develop space systems. The third and present phase is associated to the recent growth in the importance of Systems Engineering to the development of the contemporary large and complex systems. This paper is a summary review of the history of Systems Engineering at INPE from its inception to the present.

Current systems such as satellites, aircrafts, automobiles, turbines, wind power generators and traffic controls are becoming increasingly complex and/or highly integrated as prescribed by the SAE-ARP-4754 Standard. Such systems frequently require accurate generation, distribution and time or phase synchronization of signals with different frequencies that may be based on one reference signal and frequency. But the environment fluctuations or the non-linear dynamics of these operations cause uncertainties (skew and jitter) in the phase or time of the reference signal and its derived signals. So, techniques to reduce those causes or their effects are becoming important aspects to consider in the design of such systems. The PLL techniques are useful for establishing coherent phase or time references, jitter reduction, skew suppression, frequency synthesis, and clock recovery in numerous systems such as communication, wireless systems, digital circuits, rotors, and others.