Search

© 2018 Elsevier Ltd Driven by the need for multi-functionality and increasing demands for low mass and compact-stowing, unfolding, self-deploying or –morphing smart mechanical structures have become popular space engineering designs for flexible appendages. Extensive research has been conducted on the use of tape springs as hinge deployment mechanisms for space booms, solar sails, or optical membranes or directly for used as antennas. However, the vibrational behaviour of tape springs and its related dynamics have rarely been addressed in detail, even though missions are underway with similarly flexible appendages installed. By conducting quasi-static bending tests on a tape spring antenna, we evidence hysteresis behaviours in both the opposite- and equal sense bending directions. Apart from the well-known snap-through buckling, the structure exhibits torsional buckling in the equal sense bending direction before collapsing. Micro-vibrational excitation triggers nonlinear jump phenomena and the period-doubling route to chaos. Using a computational tape spring model and simplified environmental loads similar to those encountered in near-Earth orbits, coupling between the first bending and torsional modes generates a dynamic instability which is predicted by a complex eigenvalue analysis step. The current study highlights that high perturbation sensitivity and system-inherent nonlinearities can lead to stability issues. In the course of designing a spacecraft with thin-walled appendages, system-level trade-offs are routinely performed. Since it is unclear how severely the vibrations of flexible appendages might affect their proper functioning or the control of the spacecraft, it is of paramount importance to validate experimentally thin-walled structures thoroughly for their dynamic and stability behaviours.

Measurements of naturally enhanced ion acoustic line (NEIAL) echoes obtained with a five-antenna interferometric imaging radar system are presented. The observations were conducted with the European Incoherent SCATter (EIS-CAT) radar on Svalbard and the EISCAT Aperture Synthesis Imaging receivers (EASI) installed at the radar site. Four baselines of the interferometer are used in the analysis. Based on the coherence estimates derived from the measurements, we show that the enhanced backscattering region is of limited extent in the plane perpendicular to the geomagnetic field. Previously it has been argued that the enhanced backscatter region is limited in size; however, here the first unambiguous observations are presented. The size of the enhanced backscatter region is determined to be less than 900 x 500 m, and at times less than 160m in the direction of the longest antenna separation, assuming the scattering region to have a Gaussian scattering cross section in the plane perpendicular to the geomagnetic field. Using aperture synthesis imaging methods volumetric images of the NEIAL echo are obtained showing the enhanced backscattering region to be aligned with the geomagnetic field. Although optical auroral emissions are observed outside the radar look direction, our observations are consistent with the NEIAL echo occurring on field lines with particle precipitation., QC 20150914

The Buccaneer Risk Mitigation Mission is the first of two nano-satellite (cubesat) flights conducted within the collaborative partnership between UNSW Canberra Space and DSTO. Scheduled to launch in December 2016, the Buccaneer Risk Mitigation Mission will flight test several key technologies and on-orbit operations for the Buccaneer Main Mission. The flight will additionally provide a platform to conduct photometric experiments with the UNSW Canberra node of the Falcon Telescope Network and provide data for the validation of astrodynamic simulations. The presentation will provide an overview of the progress to date of the space vehicle design and manufacture; payload; experimental aims and objectives; software development; UNSW Canberra ground station and details of the planned environmental stress screening campaign.

Owing to a change in the Australian government’s paradigm to increase the nations’ presence in space, Australian universities and government organisations schedule affordable, routine in-space missions using nano-satellites with off-the-shelf payloads combined with special-purpose scientific instrumentation. However, due to small characteristic lengths in nano-satellites, thin flexible mechanisms such as deployable sun sails or antennas get proportionally larger. Together with higher mass and packaging restrictions, the stability behaviour of these fragile structures poses a significant problem for the spacecraft’s overall stability and attitude control owing to both changing environmental loads and internal micro-vibrational disturbances.Here, the vibration modes of a deployable tape spring HF antenna are investigated and characterised by means of a sensitivity study. Especially torsional modes appear very sensitive to small load changes and imperfections in the material. Using a global variance-based sensitivity study it is shown that reducing thickness and density imperfections can control certain buckling modes. Various laminates in the form of uni- and bi-directional nylon and glass-fibre re-enforced scotch tapes as well as Kapton tape are experimentally tested, applied to either the full or the partial antenna. Partially laminating the antenna structure with a double layer of bi-directional glass-fibre re-enforced Scotch and Kapton tape provides highest stability and good damping properties, especially for torsional modes without compromising packaging and weight too much.

With the advent of affordable nano-satellite designs (off-the-shelf payloads, standardised launch geometries), increasingly enterprises, governmental agencies and universities have started developing their own space programs to explore the environment of Low Earth Orbits. Thin, flexible and unfolding/deployable structures are common space engineering antenna and solar panel designs owing to their lightweight and ideal packaging characteristics, which are, however, difficult to experimentally validate in a 1-g environment. Further, curvatures or discontinuities to increase functionality without violating prioritised design criteria may lead to system-level trade-offs: stability issues arising from buckling in combination with micro-vibrations which feed back to the satellite's attitude behaviour. It appears that the literature lacks a systematic investigation of these aspects. On-Earth experimental validations (static experiments, model updating) are the starting point for studying the response to static/dynamic loading of thin curved flexible structures such as deployable high frequency antennas. Linear and nonlinear buckling modes owing to varying loadings (aerodynamic drag, solar radiation pressure, residual gravity and magnetic body forces) are found together with a high sensitivity to torsional modes' frequency changes under micro-vibrational forcing.

To evaluate long-term results of low-fluence photodynamic therapy (PDT) with verteporfin in the treatment of chronic central serous chorioretinopathy (CCSC). Methods.-Retrospective medical record review of 38 eyes (34 patients) who received lowfluence PDT for the treatment of CCSC. Visual acuity (VA), fundus biomicroscopy, fluorescein angiography (FA), indocyanine green angiography (ICG) and optical coherence tomography (OCT) were analyzed. Results.-Thirty-eight eyes (34 patients) with CCSC received low-fluence PDT. Mean follow-up after PDT was 43.97 months. Mean logMar best corrected VA (BCVA) improved significantly from 0.33 to 0.11 at the last follow-up which corresponds to a gain of 2.2 lines. At 3 months, complete resolution of central subretinal fluid was achieved on OCT after 1 PDT in 37 eyes and after 2 PDTs in 1 eye (retreated at 3 months after first PDT). One patient developed choroidal neovascularization (CNV) 4 years after his low-fluence PDT and received anti-vascular endothelial growth factor (VEGF) injections. Conclusion.-Low-fluence PDT with verteporfin for CCSC seems efficacious and safe in thelong-term., SCOPUS: ar.j, info:eu-repo/semantics/published

The Horizon Oil Sands operation in Alberta, Canada, consists of a surface mine, a bitumen processing facility with associated tailings ponds and a heavy oil upgrading facility which produces synthetic crude oil. Site development began in 2004 and the largest surface disturbances are associated with mine surface soil and overburden removal and the construction of the tailings pond dyke. The first closure plan was submitted in 2002 as part of the mine application and was revised in 2006, and a new revision is scheduled to be submitted to Alberta Environment by the end of December 2011. Progressive reclamation is being integrated with the mine planning process and closure objectives will include integration of geotechnically stable landforms with surrounding landforms, the use of drainage systems designed to minimise erosion and substance loadings, ecologically sustainable end pits, forest capability, including commercial forestry, equal to pre-development conditions, development of reclaimed areas into self-sustaining ecosystems with acceptable biodiversity, on-site public health and safety protection during the life of the operation, reclamation certification for transfer of the land back to the Crown, direct placement of reclamation materials wherever possible to optimise the viability of native seed banks and propagules, natural invasion of native vegetation in ecologically receptive areas and the use of local native seed sources wherever practical., The Horizon Oil Sands operation in Alberta, Canada, consists of a surface mine, a bitumen processing facility with associated tailings ponds and a heavy oil upgrading facility which produces synthetic crude oil. Site development began in 2004 and the largest surface disturbances are associated with mine surface soil and overburden removal and the construction of the tailings pond dyke. The first closure plan was submitted in 2002 as part of the mine application and was revised in 2006, and a new revision is scheduled to be submitted to Alberta Environment by the end of December 2011. Progressive reclamation is being integrated with the mine planning process and closure objectives will include integration of geotechnically stable landforms with surrounding landforms, the use of drainage systems designed to minimise erosion and substance loadings, ecologically sustainable end pits, forest capability, including commercial forestry, equal to pre-development conditions, development of reclaimed areas into self-sustaining ecosystems with acceptable biodiversity, on-site public health and safety protection during the life of the operation, reclamation certification for transfer of the land back to the Crown, direct placement of reclamation materials wherever possible to optimise the viability of native seed banks and propagules, natural invasion of native vegetation in ecologically receptive areas and the use of local native seed sources wherever practical.