Current Issue : July - September Volume : 2013 Issue Number : 3 Articles : 5 Articles
The objective of the work reported herein was to use a systems engineering approach to guide development of integrated\r\ninstrumentation/sensor systems (IISS) incorporating communications, interconnections, and signal acquisition. These require\r\nenhanced suitability and effectiveness for diagnostics and health management of aerospace equipment governed by the principles\r\nof Condition-based maintenance (CBM). It is concluded that the systems engineering approach to IISS definition provided clear\r\nbenefits in identifying overall system requirements and an architectural framework for categorizing and evaluating alternative\r\narchitectures, relative to a bottom up focus on sensor technology blind to system level user needs. CBM IISS imperatives\r\nidentified include factors such as tolerance of the bulk of aerospace equipment operational environments, low intrusiveness, rapid\r\nreconfiguration, and affordable life cycle costs. The functional features identified include interrogation of the variety of sensor types\r\nand interfaces common in aerospace equipment applications overmultiplexed communication media with flexibility to allow rapid\r\nsystem reconfiguration to adapt to evolving sensor needs. This implies standardized interfaces at the sensor location (preferably to\r\nopen standards), reduced wire/connector pin count in harnesses (or their elimination through use of wireless communications)....
A complete global model for argon was developed and adapted to plasma reactor and plasma thruster modeling. It takes into\r\nconsideration ground level and excited Ar and Ar+ species and the reactor and thruster form factors. The electronic temperature,\r\nthe species densities, and the ionization percentage, depending mainly on the pressure and the absorbed power, have been obtained\r\nand commented for various physical conditions....
This paper presents a novel approach for the preliminary design of Low-Thrust, many-revolution transfers. The main feature of\r\nthe novel approach is a considerable reduction in the control parameters and a consequent gain in computational speed. Each\r\nspiral is built by using a predefined pattern for thrust direction and switching structure. The pattern is then optimised to minimise\r\npropellant consumption and transfer time. The variation of the orbital elements due to the thrust is computed analytically from\r\na first-order solution of the perturbed Keplerian motion. The proposed approach allows for a realistic estimation of ?V and time\r\nof flight required to transfer a spacecraft between two arbitrary orbits. Eccentricity and plane changes are both accounted for.\r\nThe novel approach is applied here to the design of missions for the removal of space debris by means of an Ion Beam Shepherd\r\nSpacecraft. In particular, two slightly different variants of the proposed low-thrust control model are used for the different phases\r\nof the mission. Thanks to their low computational cost they can be included in a multiobjective optimisation problem in which\r\nthe sequence and timing of the removal of five pieces of debris are optimised to minimise propellant consumption and mission\r\nduration....
Recently, the end-of-service life for aging aircra? and related parts has become a key subject in recycling industries worldwide. Over\r\nthe next 20 years, approximately 12,000 aircra? currently utilized for different purposes will be at the end of service. ?us, reclaiming\r\nretired aircra? by environmentally responsible methods while retaining some of the value becomes a signi??cant need. Recycling\r\naircra? components and using these in different applications will reduce the consumption of natural resources as well as land??ll\r\nallocations. Compared to the production of virgin materials, recycling aircra? will also reduce air, water, and soil contaminations,\r\nas well as energy demand. In the present study, we have investigated the environmental bene??ts of recycling and reusing aircra?\r\ncomponents in the same or similar applications as low-energy input materials. During the aircra? recycling, most of the aircra?\r\ncomponents can be recycled and reused a?er reasonable modi??cations and investments....
Carrier-phase differential GPS (CDGPS) is a promising technology for accurate relative navigation in LEO formations of\r\ncooperating satellites, but navigation filter robustness against poor GPS geometry and noisy measurements has to be improved.\r\nThis can be performed by augmenting the navigation filter with intersatellite local ranging measurements, as the ones provided by\r\nranging transponders or GNSS-like systems. In this paper, an augmented CDGPS navigation filter is proposed for the formation of\r\ntwo satellites characterized by a short, varying baseline, relevant to next generation Synthetic Aperture Radar missions. Specifically,\r\na cascade-combination of dynamic and kinematic filterswhich processes double-differenced code and carrier measurements on two\r\nfrequencies, as well as local inter-satellite ranging measurements, is used to get centimeter-level baseline estimates.The augmented\r\nfilter is validated by numerical simulations of the formation orbital path. Results demonstrate that the proposed approach is effective\r\nin preserving the centimeter-level accuracy achievable by a CDGPS-only filter also in the presence of a poor GDOP or a limited\r\nnumber of GPS satellites in view....
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