GEODA-GRUA: Adaptive Multibeam Conformal Antenna for Satellites Communications

The GEODA-GRUA is one conformal adaptive antenna array designed for satellite communications. Operating at 1.7 GHz with circular polarization, it is possible to track and communicate with several satellites at once being able to receive signals in full azimuth and within the range of 5° to broadside elevation thanks to its adaptive beam. The complex structure of the antenna array has 2700 radiating elements based on a set of 60 similar triangular arrays that are divided in 15 subarrays of 3 radiating elements. A control module governs each transmission/receiver (T/R) module associated to each cell in order to manage beam steering by shifting phases.

Robustness Analysis of Eigenstructure Assignment Controllers on Rigid-Flexible Satellites

Flexible spacecraft with attached solar panels may exhibit undesired vibrations and structural deformations. These types of vehicles show an intrinsic coupling of the elements of the structure. The attitude maneuvers performed by flexible spacecraft may cause non-desired deflections of attached flexible elements. Any attitude and orbit control system generally solves these problems using filters that are designed to attenuate the relative deflections of flexible appendages. In this paper, we propose a method for designing attitude static controllers using an eigenstructure assignment (EA) method. A set of requirements were specified from our understanding of the system modes in an open loop. Exhaustive theoretical and numerical simulations were performed on special cases to verify the controller design procedure. In the design of the controller, we considered all of the aspects that relate to the eigenstructure assignment. The primary objective of this paper is to demonstrate the feasibility of obtaining a high degree of decoupling for some selected modes via the application of an EA method. Finally a robustness analysis is perform to the system together with the designed controller by means of a mu-analysis

Parallelizing irregular and pointer-based computations automatically: perspectives from logic and constraint programming

Irregular computations pose sorne of the most interesting and challenging problems in automatic parallelization. Irregularity appears in certain kinds of numerical problems and is pervasive in symbolic applications. Such computations often use dynamic data structures, which make heavy use of pointers. This complicates all the steps of a parallelizing compiler, from independence detection to task partitioning and placement. Starting in the mid 80s there has been significant progress in the development of parallelizing compilers for logic pro­gramming (and more recently, constraint programming) resulting in quite capable paralle­lizers. The typical applications of these paradigms frequently involve irregular computations, and make heavy use of dynamic data structures with pointers, since logical variables represent in practice a well-behaved form of pointers. This arguably makes the techniques used in these compilers potentially interesting. In this paper, we introduce in a tutoríal way, sorne of the problems faced by parallelizing compilers for logic and constraint programs and provide pointers to sorne of the significant progress made in the area. In particular, this work has resulted in a series of achievements in the areas of inter-procedural pointer aliasing analysis for independence detection, cost models and cost analysis, cactus-stack memory management, techniques for managing speculative and irregular computations through task granularity control and dynamic task allocation such as work-stealing schedulers), etc.

Automatic parallelization of irregular and pointer-based computations: perspectives from logic and constraint programming

Irregular computations pose some of the most interesting and challenging problems in automatic parallelization. Irregularity appears in certain kinds of numerical problems and is pervasive in symbolic applications. Such computations often use dynamic data structures which make heavy use of pointers. This complicates all the steps of a parallelizing compiler, from independence detection to task partitioning and placement. In the past decade there has been significant progress in the development of parallelizing compilers for logic programming and, more recently, constraint programming. The typical applications of these paradigms frequently involve irregular computations, which arguably makes the techniques used in these compilers potentially interesting. In this paper we introduce in a tutorial way some of the problems faced by parallelizing compilers for logic and constraint programs. These include the need for inter-procedural pointer aliasing analysis for independence detection and having to manage speculative and irregular computations through task granularity control and dynamic task allocation. We also provide pointers to some of the progress made in these áreas. In the associated talk we demónstrate representatives of several generations of these parallelizing compilers.

Untainted puncturing for irregular low-density parity-check codes

Puncturing is a well-known coding technique widely used for constructing rate-compatible codes. In this paper, we consider the problem of puncturing low-density parity-check codes and propose a new algorithm for intentional puncturing. The algorithm is based on the puncturing of untainted symbols, i.e. nodes with no punctured symbols within their neighboring set. It is shown that the algorithm proposed here performs better than previous proposals for a range of coding rates and short proportions of punctured symbols.

The Irregular Ribbed Vault of the Sacristy of the Cathedral of Saint-Jean Baptiste in Perpignan

The vault of the sacristy of the Cathedral of Saint-Jean Baptiste in Perpignan (France), constructed by the Majorcan architect Guillem Sagrera between 1433 and 1447, is an outstanding, yet strikingly unknown, example of rib vaulting. This paper analyzes the overall construction of the form of the vault, characterized by its highly irregular perimeter, with particular attention to an isolated decorated corbel which solves the problem of the wall support of a group of six ribs and is in stark contrast with the rest of the supports, which are completely unadorned. Given the extreme rigour of Sagrera in all his works (and this one in particular), this apparent “capriccio” must be justified not only by decorative or formal requirements, but also by the constructive logic of Gothic vaulting system

Analysis of irregular behaviour on an optical computing logic cell

A new methodology to study irregular behaviours in logic cells is reported. It is based on two types of diagrams, namely phase and working diagrams. Sets of four bits are grouped and represented by their hexadecimal equivalent. Some hexadecimal numbers correspond to certain logic functions. The influence of the internal and external tolerances, namely those appearing in the employed devices and in the working signals, may be analysed with this method. Its importance in the case of logic structures with chaotic behaviours is studied.

Analysis of bare-tether systems for deorbiting low-earth-orbit satellites

Performances, design criteria, and system mass of bare tethers for satellite deorbiting missions are analyzed. Orbital conditions and tether cross section define a tether length, such that 1) shorter tethers are electron collecting practically in their whole extension and 2) longer tethers collect practically the short-circuit current in a fixed segment length. Long tethers have a higher drag efficiency (defined as the drag force vs the tether mass) and are better adapted to adverse plasma densities. Dragging efficiency and mission-related costs are used to define design criteria for tether geometry. A comparative analysis with electric thrusters shows that bare tethers have much lower costs for low- and midinclination orbits and remain an attractive option up to 70 deg.

An universal system to de-orbit satellites at end of life

A 3-year Project financed by the European Commission is aimed at developing a universal system to de-orbit satellites at their end of life, as a fundamental contribution to limit the increase of debris in the Space environment. The operational system involves a conductive tapetether left bare to establish anodic contact with the ambient plasma as a giant Langmuir probe. The Project will size the three disparate dimensions of a tape for a selected de-orbit mission and determine scaling laws to allow system design for a general mission. Starting at the second year, mission selection is carried out while developing numerical codes to implement control laws on tether dynamics in/off the orbital plane; performing numerical simulations and plasma chamber measurements on tether-plasma interaction; and completing design of subsystems: electronejecting plasma contactor, power module, interface elements, deployment mechanism, and tether-tape/end-mass. This will be followed by subsystems manufacturing and by currentcollection, free-fall, and hypervelocity impact tests.

Extension of Euskalduna Conference Centre and Concert Hall: A Contemporary Application of Irregular Reciprocal Frames

Reciprocal frame structures, formed by a set of self-supported elements in a closed circuit, have long been used since antiquity to cover large spans with small elements. The roof structure of the Euskalduna conference centre and concert hall extension in Bilbao, covering an irregu- lar geometry of 3000 m2 with a maximum span of 45 m, presented an interesting opportunity to revisit the concept and to apply these classical systems. Furthermore, its analysis and develop- ment led to an interesting discussion on reciprocal frames. They showed great sensitivity of these systems to the local modification of a particular element, establishment of irregular load paths, mobilisation of almost the entire sys- tem when locally applying a punctual load and, finally, its large deformability. Besides, reciprocal frames present particular construction complexities and possibilities due to the moderate length of the structural elements, the predominance of shear-only connec- tions and the necessity of the entire system to be completely erected to guarantee its stability. Euskalduna extension, completed in 2012, is one of the largest and a very par- ticular case of irregular reciprocal frame structures built in the world. It shows the formal possibilities and potentiality of reciprocal frames to respond to free and irregular geometries.

Long-term dynamics of fast rotating tethers around planetary satellites

We derive a semi-analytic formulation that enables the study of the long-term dynamics of fast-rotating inert tethers around planetary satellites. These equations take into account the coupling between the translational and rotational motion, which has a non-negligible impact on the dynamics, as the orbital motion of the tether center of mass strongly depends on the tether plane of rotation and its spin rate, and vice-versa. We use these governing equations to explore the effects of this coupling on the dynamics, the lifetime of frozen orbits and the precession of the plane of rotation of the tether.

Efficient Irregular Tessellations

Investigación sobre teselaciones irregulares eficientes, con la aplicación en la construcción de un prototipo físico. El prototipo es un casquete semiesférico de 2m de diámetro desarrollado con herramientas de diseño paramétrico y fabricación digital.

Magnetic Attitude Control for Satellites in Polar or Sun-Synchronous Orbits

In this work, a new law for magnetic control of satellites in near-polar orbits is presented. This law has been developed for the UMPSat-2 microsatellite, which has been designed and manufactured by Universidad Politécnica de Madrid, Madrid. The control law is a modification of the B-dot strategy that enables the satellite to control the rotation rate. Besides, the satellite?s equilibrium state is characterized by having the rotation axis perpendicular to the orbit?s plane. The control law described in the present work only needs magnetometers and magnetorquers, as sensors and actuators, respectively, to carry out a successful attitude control on the spacecraft. A description of the analysis is included. Performance and applicability of the proposed method have been demonstrated by control dynamics together with Monte Carlo techniques and by implementing the control law in the UPMSat-2 mission simulator. Results show good performance in terms of acquisition and stability of the satellite rotation rate and orientation with respect to its orbit?s plane.

Optimum sizing of bare-tape tethers for de-orbiting satellites at end of mission

De-orbiting satellites at end of mission would prevent generation of new space debris. A proposed de-orbit technology involves a bare conductive tape-tether, which uses neither propellant nor power supply while generating power for on-board use during de-orbiting. The present work shows how to select tape dimensions for a generic mission so as to satisfy requirements of very small tether-to-satellite mass ratio mt/MS and probability Nf of tether cut by small debris, while keeping de-orbit time tf short and product tf ×× tether length low to reduce maneuvers in avoiding collisions with large debris. Design is here discussed for particular missions (initial orbit of 720 km altitude and 63° and 92° inclinations, and 3 disparate MS values, 37.5, 375, and 3750 kg), proving it scalable. At mid-inclination and a mass-ratio of a few percent, de-orbit time takes about 2 weeks and Nf is a small fraction of 1%, with tape dimensions ranging from 1 to 6 cm, 10 to 54 μμm, and 2.8 to 8.6 km. Performance drop from middle to high inclination proved moderate: if allowing for twice as large mt/MS, increases are reduced to a factor of 4 in tf and a slight one in Nf, except for multi-ton satellites, somewhat more requiring because efficient orbital-motion-limited electron collection restricts tape-width values, resulting in tape length (slightly) increasing too.

Emulation of an OWC Ocean Energy Plant With PMSG and Irregular Wave Model

Ocean energy is a promising resource for renewable electricity generation that presents many advantages, such as being more predictable than wind energy, but also some disadvantages such as large and slow amplitude variations in the generated power. This paper presents a hardware-in-the-loop prototype that allows the study of the electric power profile generated by a wave power plant based on the oscillating water column (OWC) principle. In particular, it facilitates the development of new solutions to improve the intermittent profile of the power fed into the grid or the test of the OWC behavior when facing a voltage dip. Also, to obtain a more realistic model behavior, statistical models of real waves have been implemented.