Semi-analytical guidance algorithm for autonomous close approach to non-cooperative low-gravity targets

An adaptive guidance algorithm for close approach to and precision landing on uncooperative low-gravity objects (e.g. asteroids) is proposed. The trajectory, updated by means of a minimum fuel optimal control problem solving, is expressed in a polynomial form of minimum order to satisfy a set of boundary constraints from initial and final states and attitude requirements. Optimal guidance computation, achieved with a simple two-stage compass search, is reduced to the determination of three parameters, time-of-flight, initial thrust magnitude and initial thrust angle, according to additional constraints due to actual spacecraft architecture. A NEA landing mission case is analyzed

Chitosan and its char as fillers in cement-base composites: A case study

Abstract The continuous research of new functional materials combining both advanced properties and increased sustainability has dramatically risen up in the last decades. Instead of searching for new solutions, composites (formed by a combination of already present materials) are subject of different studies due to their capability of merging the advantages of components. Hence, chitosan, a biowaste-derived biopolymer, has been thermally-converted into chars by pyrolysis treatment. Subsequently, both chitosan and its char are introduced into cementitious matrix forming cement-based composites. The analysis of the mechanical properties of these materials evidenced that char-containing composites show an incipient fracture toughness capability, very appealing for possible structural applications

Mechanical properties of mortar containing recycled Acanthocardia tuberculata seashells as aggregate partial replacement

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Mechanical properties of mortar containing recycled Acanthocardia tuberculata seashells as aggregate partial replacement

Waste management is a most current topic, and as such, numerous articles in literature discuss over the recycling and re-use of waste materials from various fields. A common solution is the to use these materials as partial substituent of the inert fraction in concretes and mortars. This work focuses on the possibility of using Acanthocardia tuberculata seashells, which constitute a food waste destined to landfilling, as partial substituents of inert in mortars. The results obtained evidenced that the reduction in mechanical properties (in terms of toughness and flexural stress) is mainly due to the water absorption properties of seashells aggregates, which affect the hydration of the cement. However, as experimentally demonstrated, such decrease in mechanical properties in any case does not compromise the performance of the material when used for civil applications

The HERMES-technologic and scientific pathfinder

HERMES-TP/SP (High Energy Rapid Modular Ensemble of Satellites Technologic and Scientific Pathfinder) is a constellation of six 3U nano-satellites hosting simple but innovative X-ray detectors, characterized by a large energy band and excellent temporal resolution, and thus optimized for the monitoring of Cosmic High Energy transients such as Gamma Ray Bursts and the electromagnetic counterparts of Gravitational Wave Events, and for the determination of their positions. The projects are funded by the Italian Ministry of University and Research and by the Italian Space Agency, and by the European Union's Horizon 2020 Research and Innovation Program under Grant Agreement No. 821896. HERMES-TP/SP is an in-orbit demonstration, that should be tested starting from 2022. It is intrinsically a modular experiment that can be naturally expanded to provide a global, sensitive all sky monitor for high-energy transients

A Highly Integrated Navigation Unit for On-Orbit Servicing Missions

VINAG (VISION/INS integrated Navigation Assisted by GNSS) is a highly integrated multisensor navigation unit, particularly conceived for On-Orbit Servicing missions. The system is designed to provide all-in-one, on-board real time autonomous absolute navigation as well as pose determination of an uncooperative known object orbiting in LEO (Low Earth Orbit), GEO (GEosynchronous Orbits) and possibly in HEO (Highly Earth Orbit). The system VINAG is under development by a team of Italian companies and universities, co-financed by the Italian Space Agency. Thanks to a tight optimized integration of its subsystems, VINAG is characterized by a low power and mass total budgets and therefore it is suitable for small and very small satellites. In order to provide both 1) absolute orbit and attitude determination and 2) vision-based pose determination, the unit integrates three metrology systems: a Cameras Subsystem (a monocular camera and a Star sensor), an Inertial Measurement Unit (IMU) and a GNSS (Global Navigation Satellite System) receiver. In this paper, we introduce the complete system architecture, the adopted algorithms and then the adopted hardware design solutions. In addition, we describe preliminary numerical simulation results obtained for different orbits from LEO to GEO carried out for the validation phase of VINAG