Cooperative Platooning and Servicing for Spacecraft Formation Flying using Model Predictive Control

This work was partially funded by FCT project REPLACE (PTDC/EEIAUT/32107/2017) which includes Lisboa 2020 and PIDDAC funds, project CAPTURE (PTDC/EEIAUT/1732/2020).This paper addresses two complementary problems of spacecraft formation flying, namely spacecraft platooning and on-orbit spacecraft servicing, using Model Predictive Control (MPC). With the proposed solutions, these space formation scenarios can be regarded as a cooperative system composed of several spacecraft with a common goal, which may have clear advantages relative to other approaches. For each application scenario, a different optimization problem and MPC design is presented, including relevant constraints to deal with physical limitations, visibility problems, and also to guarantee a collision-free trajectory from other spacecraft or obstacles. The proposed methods are validated with realistic simulation results, showing that all vehicles demonstrate reliable performance following a given trajectory or goal in a formation, while satisfying all the considered constraints.publishersversionpublishe

Benchmarking some Portuguese S&T system research units: 2nd Edition

The increasing use of productivity and impact metrics for evaluation and comparison, not only of individual researchers but also of institutions, universities and even countries, has prompted the development of bibliometrics. Currently, metrics are becoming widely accepted as an easy and balanced way to assist the peer review and evaluation of scientists and/or research units, provided they have adequate precision and recall. This paper presents a benchmarking study of a selected list of representative Portuguese research units, based on a fairly complete set of parameters: bibliometric parameters, number of competitive projects and number of PhDs produced. The study aimed at collecting productivity and impact data from the selected research units in comparable conditions i.e., using objective metrics based on public information, retrievable on-line and/or from official sources and thus verifiable and repeatable. The study has thus focused on the activity of the 2003-06 period, where such data was available from the latest official evaluation. The main advantage of our study was the application of automatic tools, achieving relevant results at a reduced cost. Moreover, the results over the selected units suggest that this kind of analyses will be very useful to benchmark scientific productivity and impact, and assist peer review.Comment: 26 pages, 20 figures F. Couto, D. Faria, B. Tavares, P. Gon\c{c}alves, and P. Verissimo, Benchmarking some portuguese S\&T system research units: 2nd edition, DI/FCUL TR 13-03, Department of Informatics, University of Lisbon, February 201

Entre la Historia y la propaganda: las dos sublevaciones del acorazado Jaime I en Julio de 1936

La consulta de la causa criminal 1189/39 instruida en plena Guerra Civil por la Auditoría del Departamento Marítimo del Ferrol permite revisar las hipótesis sobre lo acontecido a bordo del acorazado Jaime I en julio 1936, pudiendo establecerse con claridad el papel asumido por los protagonistas presentes: los oficiales golpistas y los cabos defensores de la legalidad republicana. Más allá de la minuciosidad episódica, se pone fin a la manipulación histórica de una realidad muy diferente a la difundida por los aparatos ideológicos del Estado franquista

Um sistema P2P adaptável a diferentes contextos de utilização

No mundo actual em que vivemos tudo e todos estão conectados por uma rede global denominada Internet, onde as aplicações P2P proliferam. Com a crescente evolução da Internet tem-se vindo a observar um aumento na utilização de soluções P2P, que devido à sua imprevisibilidade trazem fortes problemas para os fornecedores de serviços (e.g. ISPs). Este artigo apresentará um sistema P2P baseado no protocolo BitTorrent de fácil integração na rede Internet através da sua capacidade de adaptação a diferentes contextos de utilização. Esta integração será alcançada recorrendo a vários mecanismos e estratégias implementadas no sistema desenvolvido. A arquitectura a desenvolver será avaliada e testada com o auxilio da ferramenta de simulação NS-2, com o objectivo de testar os mecanismos propostos e analisar os resultados obtidos

Kinematic analysis and upper limb contributions to racket head velocity of elite tennis players in tennis forehand drive winner.

Mestrado em Treino de Alto RendimentoThe aim of the present study was to quantify and compare kinematic variables and their contributions to the racket head speed in tennis forehand winner, in the cross court and inside out direction. Mini inertial sensors (Xsens MVN) of motion capture, recorded kinematic data of six elite tennis players (ATP professionals). Linear velocity of the racket and ball were captured with a high speed video camera. Results indicate that the direction of the shot is influenced by the internal/external rotation of the upper arm and the abduction/adduction of the hand after the impact. Significant differences between the two directions were found in the end of the racket horizontal movement, where the players showed higher wrist abduction when playing in the inside out direction (cross court: 13.9 ± 17.2°; inside out: 16.9 ± 18.6°). Players presented a higher internal rotation of the shoulder in the inside out direction (cross court: -54.0 ± 11.8°vs. inside out: -48.0 ± 11.0°) and demonstrated an increased racket linear velocity in the cross court direction (cross court: 32.0±3.5m/s vs. Inside out: 30.3±3.8m/s). Horizontal flexion/abduction of the upper arm and flexion/extension of the forearm were the major contributors for the racket’s head speed.Resumo: O objetivo do presente estudo foi comparar variáveis cinemáticas entre uma direita cruzada e descruzada no ténis e quantificar a contribuição do membro superior para a velocidade da cabeça da raquete Foram utilizados mini sensores inerciais (Xsens MVN) para capturar o movimento de seis atletas profissionais (ranking ATP). Para capturar a velocidade da raquete e da bola foi utilizada uma câmara de alta velocidade, onde a velocidade foi calculada através de um algoritmo DLT com o software APAS®. A contribuição do membro superior para a velocidade da cabeça da raquete foi identificada através de um algoritmo matemático. Foram selecionados 12 batimentos por sujeito que foram analisados desde o final da fase de preparação até ao final do movimento horizontal da raquete. Os resultados do indicam que a direção da bola poderá ser influenciada pela rotação interna do braço e a abdução da mão após o batimento. Os jogadores apresentaram maior abdução na direita descruzada (cruzada: 13.9 ± 17.2°; descruzada: 16.9 ± 18.6°) e maior rotação interna do ombro na direita descruzada (cruzada: -54.0 ± 11.8° vs. descruzada: -48.0 ± 11.0°). Ficou demonstrado que a maior contribuição para a velocidade da raquete provém da flexão/abdução do braço e também da flexão/extensão do antebraço