Nonlinear analysis of a simple model of temperature evolution in a satellite

We analyze a simple model of the heat transfer to and from a small satellite orbiting round a solar system planet. Our approach considers the satellite isothermal, with external heat input from the environment and from internal energy dissipation, and output to the environment as black-body radiation. The resulting nonlinear ordinary differential equation for the satellite’s temperature is analyzed by qualitative, perturbation and numerical methods, which prove that the temperature approaches a periodic pattern (attracting limit cycle). This approach can occur in two ways, according to the values of the parameters: (i) a slow decay towards the limit cycle over a time longer than the period, or (ii) a fast decay towards the limit cycle over a time shorter than the period. In the first case, an exactly soluble average equation is valid. We discuss the consequences of our model for the thermal stability of satellites.

Networked Utopia : the Architecture and Urbanism of the Bata Shoe Company Satellite Cities = Utopia en red : arquitectura y urbanismo en las ciudades satélite de la Bata Shoe Company, 1930 al presente

From its humble beginnings as a small workshop established by Tomáš Baťa in 1874, the Bata Shoe Company became a gigantic concern in the 1920s, built on the principles of scientific management and welfare capitalism. The growth of the company engulfed Zlín (in today’s Czech Republic), its hometown, and transformed it into a modern industrial garden city satisfying the needs of both a growing industrial population, and those of the company itself. As a reaction to the aftermath of the crisis of 1929, the enterprise began a strategy of decentralization and international expansion characterized by the design and construction of a series of modern industrial towns that replicated the model of Zlín around the globe. This study is an exhaustive survey of these cities, their rationale, design, and their postindustrial conditions; it is a comparative work that has used field trips, photography, interviews, and archival material to explain the logics behind Bata’s project, to document the design and implementation of the model to multiple contexts and geographies, and to evaluate of the urban legacy of this undertaking. Finally, the research explores the question of what can the design disciplines, and other parties involved, learn from a full synthesis on the history and urbanism of the Bata satellite cities with regard to the re-imagination and sustainability of contemporary industry-sponsored interventions in developing geographies. RESUMEN Con origen en un humilde y pequeño taller fundado en 1874 por Tomáš Baťa, la Bata Shoe Company creció hasta convertirse en una gigantesca empresa en los anos 20, fundada en principios de control científico de la producción y capitalismo de bienestar. El crecimiento de la compañía se extendió por Zlín (en la actual República Checa), su pueblo de nacimiento, y la transformó en una moderna ciudad jardín industrial capaz de satisfacer las necesidades tanto de una población en alza como de la propia empresa. Como reacción a la crisis de 1929, Bata inició una estrategia de descentralización y expansión internacional caracterizada por el proyecto y construcción de modernas ciudades industriales que replicaron el modelo de Zlín por el mundo. Esta tesis es un estudio exhaustivo de estas ciudades: las razones detrás del proyecto, su diseño, y su condición post-industrial; es un estudio comparativo que se ha servido de trabajo de campo, documentación fotográfica, entrevistas y materiales de archivo para explicar la lógica detrás del proyecto de Bata, documentar el diseño e implementación de tal modelo en múltiples contextos y geografías, y valorar el legado urbano de esta empresa. Finalmente, la investigación evalúa qué podrían aprender las disciplinas del diseño y otras partes implicadas de una síntesis completa de la historia y el urbanismo de las ciudades satélite de Bata, en lo relativo a la reinvención y sostenibilidad de proyectos contemporáneos de la industria en geografías en desarrollo.

A Transportable Reflectarray Antenna for Satellite Ku-band Emergency Communications

The design of a Ku-band reconfigurable reflectarray antenna for emergency satellite communications is presented. Bidirectional high data rate satellite links are needed in emergency conditions where other telecommunication infrastructures are not available. In order to operate in this type of scenario, an antenna should be deployable, transportable, and easily repointable. The need of an automatic and fast satellite location and pointing system leads to a completely electronic reconfigurable antenna. The operative bandwidth is from 10.7 to 12.5 GHz for reception and from 14 up to 14.5 GHz for transmission (30% of relative bandwidth). The selected antenna architecture is based on a dual reflectarray system comprising a passive subreflectarray and an active main reflectarray made of reconfigurable 1-bit elementary cells based on PIN diodes.

Reflectarray antennas for dual polarization and broadband telecom satellite applications

A reflectarray antenna with improved performance is proposed to operate in dual-polarization and transmit-receive frequencies in Ku-band for broadcast satellite applications. The reflectarray element contains two orthogonal sets of four coplanar parallel dipoles printed on two surfaces, each set combining lateral and broadside coupling. A 40-cm prototype has been designed, manufactured, and tested. The lengths of the coupled dipoles in the reflectarray cells have been optimized to produce a collimated beam in dual polarization in the transmit and receive bands. The measured radiation patterns confirm the high performance of the antenna in terms of bandwidth (27%), low losses, and low levels of cross polarization. Some preliminary simulations at 11.95 GHz for a 1.2-m antenna with South American coverage are presented to show the potential of the proposed antenna for spaceborne antennas in Ku-band.