541 research outputs found
Performances of a GNSS receiver for space-based applications
No full textSpace Vehicle (SV) life span depends on its station keeping capability. Station keeping is the ability of the vehicle to maintain position and orientation. Due to external perturbations, the trajectory of the SV derives from the ideal orbit. Actual positioning systems for satellites are mainly based on ground equipment, which means heavy infrastructures. Autonomous positioning and navigation systems using Global Navigation Satellite Systems (GNSS) can then represent a great reduction in platform design and operating costs. Studies have been carried out and the first operational systems, based on GPS receivers, become available. But better availability of service could be obtained considering a receiver able to process GPS and Galileo signals. Indeed Galileo system will be compatible with the current and the modernized GPS system in terms of signals representation and navigation data. The greater
availability obtained with such a receiver would allow
significant increase of the number of point solutions and
performance enhancement. For a mid-term perspective Thales Alenia Space finances a PhD to develop the concept of a reconfigurable receiver able to deal with both the GPS system and the future Galileo system. In this context, the aim of this paper is to assess the performances of a receiver designed for Geosynchronous Earth Orbit (GEO) applications. It is shown that high improvements are obtained with a receiver designed to track both GPS and Galileo satellites. The performance assessments have been used to define the specifications of the future satellite GNSS receiver
Oribatid mites (Acari: Oribatida) of Beauchêne Island, Falklands, South Atlantic
No full textA total of 12 species of oribatid mites (Acari: Oribatida) are reported from Beauchêne Island, including two new species. Furcobates lewissmithi n. sp. and Oribatella blocki n. sp. are described and figured
On a mixed Monge-Ampere operator for quasiplurisubharmonic functions with analytic singularities
No full textWe consider mixed Monge-Ampere products of quasiplurisubharmonic functions with analytic singularities, and show that such products may be regularized as explicit one-parameter limits of mixed Monge-Ampere products of smooth functions, generalizing results of Andersson, Blocki and the last author in the case of non-mixed Monge-Ampere products. Connections to the theory of residue currents, going back to Coleff-Herrera, Passare and others, play an important role in the proof. As a consequence we get an approximation of Chern and Segre currents of certain singular hermitian metrics on vector bundles by smooth forms in the corresponding Chern and Segre classes
Finite Element calculations of heat transfer for the Forward SCT ModulesPart II - the Inner Module ATL-COM-INDET-2000-015
No full textA status report on the thermal performance of the baseline SCT inner forward modules is presented. In order to understand improvements of the thermal behaviour, design changes that have been proposed elsewhere for the outer module, and which lead to significant improvements of the thermal characteristics of the modules, have been applied to the inner module
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