References of "Acta Astronautica"
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See detailA novel SETI strategy targeting the solar focal regions of the most nearby stars
Gillon, Michaël ULg

in Acta Astronautica (2013), 94

Many hypotheses have been raised to explain the famous Fermi paradox. One of them is that self-replicating probes could have explored the whole Galaxy, including our Solar System, and that they are still ... [more ▼]

Many hypotheses have been raised to explain the famous Fermi paradox. One of them is that self-replicating probes could have explored the whole Galaxy, including our Solar System, and that they are still to be detected. In this scenario, it is proposed here that probes from neighboring stellar systems could use the stars they orbit as gravitational lenses to communicate efficiently with each other. Under this hypothesis, a novel SETI approach would be to monitor the solar focal regions of the most nearby stars to search for communication devices. The envisioned devices are probably not detectable by imagery or stellar occultation, but an intensive multi-spectral monitoring campaign could possibly detect some communication leakages. Another and more direct option would be to message the focal regions of nearby stars in an attempt to initiate a reaction. [less ▲]

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See detailA Xylophone Bar Magnetometer for micro/pico satellites
Lamy, Hervé; Niyonzima, Innocent ULg; Rochus, Pierre ULg et al

in Acta Astronautica (2010), 67(7-8), 793-809

The Belgian Institute of Space Aeronomy (BIRA-IASB), "Centre Spatial de Liège" (CSL), "Laboratoire de Techniques Aéronautiques et Spatiales" (LTAS) of University of Liège, and the Microwave Laboratory of ... [more ▼]

The Belgian Institute of Space Aeronomy (BIRA-IASB), "Centre Spatial de Liège" (CSL), "Laboratoire de Techniques Aéronautiques et Spatiales" (LTAS) of University of Liège, and the Microwave Laboratory of University of Louvain-La-Neuve (UCL) are collaborating in order to develop a miniature version of a xylophone bar magnetometer (XBM) using Microelectromechanical Systems (MEMS) technology. The device is based on a classical resonating xylophone bar. A sinusoidal current is supplied to the bar oscillating at the fundamental transverse resonant mode of the bar. When an external magnetic field is present, the resulting Lorentz force causes the bar to vibrate at its fundamental frequency with an amplitude directly proportional to the vertical component of the ambient magnetic field. In this paper we illustrate the working principles of the XBM and the challenges to reach the required sensitivity in space applications (measuring magnetic fields with an accuracy of approximately of 0.1 nT). The optimal dimensions of the MEMS XBM are discussed as well as the constraints on the current flowing through the bar. Analytical calculations as well as simulations with finite element methods have been used. Prototypes have been built in the Microwave Laboratory using Silicon on Insulator (SOI) and bulk micromachining processes. Several methods to accurately measure the displacement of the bar are proposed. [less ▲]

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See detailDynamic analysis of the self-locking phenomenon in tape spring hinges
Hoffait, Sébastien ULg; Bruls, Olivier ULg; Granville, Didier et al

in Acta Astronautica (2010), 66(7-8), 1125-1132

This paper investigates the dynamic behaviour of tape-spring hinges that are commonly used in space deployable structures. During the deployment of an appendice (e.g. a solar panel or a beam), a tape ... [more ▼]

This paper investigates the dynamic behaviour of tape-spring hinges that are commonly used in space deployable structures. During the deployment of an appendice (e.g. a solar panel or a beam), a tape-spring hinge allows the simultaneous achievement of the actuating, guiding and self-locking functions without friction elements. The proposed finite element model is able to capture buckling and hysteresis phenomena, which have a strong influence on the 3D motion of the system. A detailed analysis of those effects is developed, leading to a physical explanation of the crucial self-locking phenomenon. [less ▲]

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See detailOptical methods for non-contact measurements of membranes
Roose, Stéphane ULg; Stockman, Yvan ULg; Rochus, Pierre ULg et al

in Acta Astronautica (2009), 65(9-10), 1317-1329

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film ... [more ▼]

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film membranes. Their inherent properties (low mass and small thickness) preclude the use of conventional measurement methods (accelerometers and displacement transducers for example) during on-ground testing. In this context, innovative non-contact measurement methods need to be investigated for these stretched membranes. The object of the present project is to review existing measurement systems capable of measuring characteristics of membrane space-structures such as: dot-projection videogrammetry (static measurements), stereo-correlation (dynamic and static measurements), fringe projection (wrinkles) and 3D laser scanning vibrometry (dynamic measurements). Therefore, minimum requirements were given for the study in order to have representative test articles covering a wide range of applications. We present test results obtained with the different methods on our test articles. [less ▲]

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See detailNew applications of rapid prototyping and rapid manufacturing (RP/RM) technologies for space instrumentation
Rochus, Pierre ULg; Plesseria, Jean-Yves ULg; van Elsen, M. et al

in Acta Astronautica (2007), 61

In the frame of a research project, CRIF, KUL and CSL have investigated the possibility to use rapid prototyping and rapid manufacturing (RP/RM) techniques during space instrument development. Rapid ... [more ▼]

In the frame of a research project, CRIF, KUL and CSL have investigated the possibility to use rapid prototyping and rapid manufacturing (RP/RM) techniques during space instrument development. Rapid prototyping and rapid manufacturing terms gather several techniques with the common baseline that parts are built layer by layer, starting from a CAD model. These techniques imply powder, paste or liquid and are applicable to polymers, ceramics and metals. In a first step, the major advantages of these techniques have been presented to Belgian industries implied in the space sector and, as a result of the discussions, development goals for the project have been identified. Several types of use have also been pointed, from demonstration mock-up to real space hardware. In parallel to technical developments, several case studies and tests have been performed. The case studies have shown that the rapid manufacturing allows complex geometries to be created. A drastic decrease of the number of separate parts and bolted junctions ease the predictability of the mechanical and thermal behaviour and limit the risk of imperfect junction. As a result of the project, a guidelines document has been issued to give as much information as possible on how to perform a space instrument design using the advantages of RP/RM techniques. [less ▲]

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See detailSimulation and graphical representation of the orbit and the imaging parameter of Earth observation satellites
Vandenrijt, Jean-François ULg

in Acta Astronautica (2005), 57(2-8, JUL-OCT), 186-196

Synthetic aperture radar (SAR) satellites are widely used for Earth observation applications as weather conditions and cloudiness do not affect them. However, in order to be usable, data provided by those ... [more ▼]

Synthetic aperture radar (SAR) satellites are widely used for Earth observation applications as weather conditions and cloudiness do not affect them. However, in order to be usable, data provided by those satellites need to be processed. This processing requires determination of imaging parameters that are closely linked to the spacecraft position and velocity on its orbit. For example, the difference in velocity of the Earth's surface and the spacecraft produces Doppler shift in the received signal. This decay, called Doppler centroid, is one of the most important parameters required by spaceborne SAR signal processing. As an illustration, the Antarctic anomaly that occurred in ERS data processing induced severe azimuth ambiguities ("ghosting") in the whole image. Those parameters also vary in relation to the attitude angles of the platform. In order to estimate the Doppler centroid, determination of orbital parameters and their evolution has to be made. In this paper, the method to perform orbital osculating elements calculation and imaging parameters determination for SAR satellites, starting from state vectors or two-line elements files and attitude angles, will be introduced as well as the perturbation due to the Earth flatness, called the J2 perturbation. The near-circular orbit often used by Earth observation satellites makes the perturbation equations of the J2 parameter unstable, and the introduction of new orbital parameters is required in order to be able to determine the evolution of the orbital parameters. Simulations will be performed and the resulting osculating elements will be presented and explained for short-term and long-term variations for different kinds of orbits, such as GEO, SSO, LEO and Molnya-orbit. Full analysis of the imaging parameters will be made for the SAOCOM satellite with particular attention to the Doppler centroid phenomenon: its sensitivity with relation to the attitude angles and the way to cancel it by setting the yaw steering dynamically. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailRole of interface deformations in Benard-Marangoni instability
Lebon, Georgy ULg; Dauby, Pierre ULg; Regnier, Vincent

in Acta Astronautica (2001), 48(5-12), 617-627

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