1,721,032 research outputs found
High-order polynomial continuation method for trajectory design in non-Keplerian environments
Full text linkOrbit generation in non-Keplerian environments poses some challenges related to the complex dynamical nature in which such trajectory exist. The absence of a parametric representation of the orbits requires an iterative approach to define families. Simple methods exist to fulfill such task, however, they are based on local information and prone to convergence/speed problems. A polynomial-based scheme is proposed to improve the search of the solutions along the orbital families, enhancing the overall speed of the process, while avoiding convergence issues. The scheme is tested in the framework of Earth–Moon system, and performances are discussed and compared to classical approaches
Optimal Configurations for Nanosatellite Formation Flying in Binary Asteroid Environment
No full textThe exploration of NEA (Near Earth Asteroids) is characterized by many problematics such as collision risks, irregular gravity fields and, in case of binary systems, multibody gravity perturbations, whose negative effects on mission design could be mitigated by the exploitation of multiple spacecraft in formation, with lower weights, dimensions and costs. Nanosatellite fully meet these needs, however, the poor control capabilities, and the strict requirements on relative dynamics to ensure the same performances of a single heavy spacecraft, request an efficient strategy to determine the suitable trajectories in this chaotic environment. The paper proposes a simple technique, based on orbit sampling and local optimization, to define a set of suitable configurations for a two-nanosatellite formation. After a quick review on the orbits determination and combination in binary asteroid environments, and the presentation of the objectives derived from the conceptual mission AIM (Asteroid Impact Mission), the local optimization algorithm is explained, paying attention to the selection of the method and its modification to best adapt to the specific problem. Then, results are presented, showing the strength and weakness points of the overall procedure, for the definition of future improvements
Nanotechnology in the treatment of inflammatory bowel diseases.
Full text linkBackground and aims: Treatment of inflammatory bowel diseases (IBD) is only aimed to block or
inhibit the pathogenetic steps of the inflammatory cascade. Side effects of systemic therapies,
poor targeting of orally administered topical drug and low adherence to prescription represent
frequent therapeutic challenges. Recent observations suggest that nanotechnology could
provide amazing advantage in this field since particles having dimension in the nanometer
scale (nanoparticles) can modify pharmacokinetic step of biologic and conventional therapeutic
agents with a better delivery of drugs within the intestinal inflammatory cells. The aim of this
review was to provide the clinician with an insight into the potential role of nanotechnology in
the treatment of IBD.
Methods: A systematic search (PubMed) for experimental studies on the treatment of intestinal
inflammation using nanotechnology for the delivery of drugs.
Results and conclusions: The size of the pharmaceutical formulation is inversely related to
specificity for inflammation. Nanoparticles can penetrate epithelial and inflammatory cells
resulting in much higher, effective and long-acting concentrations than can be obtained using
conventional delivery systems. From a practical point of view, this should lead to improvements in both efficacy and adherence to treatment, providing patients with the prospect of stable and prolonged remissions with reduced drug loadings. Reduced systemic side effects could also be expected
Nanosatellite Formation Flying to Enhance Science in Binary Asteroid Environment
No full textNano satellites are becoming more and more attractive even in planetary exploration. They have evident limitations in accomplishing interplanetary transfers by their own, but they add flexibility to the operational mission if they are thought to be the opportunity to distribute sensors in different locations as soon as the main platform arrives at the target planet. A fleet of nanosatellites, equipped either with identical or different scientific payloads can be released at the end of the interplanetary transfer to support the main probe science data collection or to add more environmental data retrieval, making the mission enhanced. Moreover, they can be released to get through harsh and dangerous environments-such as planetary ejecta and aggressive atmosphere - as scouts, preserving the safety of the main vehicle while acquiring scientifically interesting data the collection of which with a single classic size probe, would have required a largely expensive design, testing and qualification to ensure any catastrophic risk mitigation. Nano satellite delivery mitigates the risk with numerosity and flexibility. In this perspective the paper presents the study run on a nanosatellite fleet delivery around the Dydimos binary asteroid. The fleet scientific objectives are the binary gravity field reconstruction, any binary natural emission detection, 3D thermogravimetry and imaging. Therefore, a camera, a microbalance and corner cube retroreflectors is the set of selected payloads. Three combinations of 6 1U cubesat have been traded off to get the best science return according to the tight constraints imposed by the nanosatellites available technology, the harsh environment they would operate in and the science requirements. Moreover, the peculiar dynamics the gravitational binary asteroid environment provokes on vehicles flying in its proximity has been analyzed to exploit at the best its properties to minimize the nanosatellite fleet control while maximizing the desired trajectory evolution in time. To this end a precise up to date available model for the Dydimos bodies has been used, including in the well-known 3 body problem modelling, the rotational behavior of each of the asteroids. All beneficial locations around the stable L4 and L5 and unstable L1,2,3 have been traded off to design the most convenient operational lifetime of each fleet architecture. The paper presents in details the results of the three architectures design, highlighting benefits and limitations, with particular attention to nanosatellite formation flying and control by means of the natural three body gravitational environment they would operate in
Model predictive control for formation reconfiguration exploiting quasi-periodic tori in the cislunar environment
Full text linkGiven the numerous possibilities that formation flying space missions can enable, being able to design and govern relative trajectories in this scenario is fundamental. Particularly interesting, due to the installation and operation of the Lunar Gateway, which will represent the next human outpost in the cislunar environment, will be the exploitation of formation flying missions in the vicinity of this lunar station. The nonlinear dynamics by which the Earth-Moon system is characterised offers the possibility to find bounded relative trajectories which can be used to design the formation. In order to best exploit the formation potential, some reconfiguration manoeuvres can be used, which by changing the relative geometry can increase the versatility and adaptation of the mission. In this paper, a Model Predictive Guidance and Control strategy is proposed and applied to perform rephasing manoeuvres in the harsh environment of the Near Rectilinear Halo Orbits. By including first a limited thrust constraint and then a collision avoidance, a more mission-oriented approach is provided to the system. To further increase the robustness of the on-board algorithms, an adaptive logic is provided to the different tuning weights involved in the Model Predictive Control scheme. In this way, a more flexible system is obtained, which is capable of optimally working also in the presence of a high-fidelity simulation scenario, including discrepancies with the simplified on-board dynamical model
Formation flying orbits and GNC design in binary asteroid systems
Full text linkFormation flying represents a promising opportunity for next space missions, due to its benefits in cost saving, redundancy and fault tolerance given by multiple small and cheap space segments exploitation, with comparable performance of a single, large monolithic spacecraft. That is even more relevant in asteroid exploration, as the harsh environment poses great risks to the probes survival. The low, irregular gravity field, the poor knowledge of shape and composition, and the possible presence of floating particles in the surroundings suggest adopting a low-risk strategy for the exploration of these bodies, delegating proximity operations to multiple nanosatellites, while keeping the main spacecraft at safe distance. As a downside, multiple cooperating spacecraft imply advanced capabilities in accurately reconstructing the relative positions and displacements and in fixing reconfiguration manoeuvres. Moreover, whenever relative distance is very close, agents’ guidance and control shall be autonomously computed by the spacecraft, as promptness of commands is not ensured relying on ground segment only. The partially unknown environment exacerbates this issue, demanding navigation and control schemes capable of withstanding potentially large uncertainties in the dynamics. If a binary system is considered, the multiple gravitational sources complicate even more the setup of the formation, requiring an accurate search and selection of operative orbits. This study will be thus defined by three different steps. First the search and development of suitable trajectories to host a reconfigurable satellite formation is carried out. Then the design of a Model Predictive on-board guidance and control law is performed to assess the capability of the spacecraft to execute successful reconfiguration transfers relying on a simplified dynamical model (namely the Circular Restricted Three-Body Problem). At the end the navigation error requirements are derived, in order to ensure the feasibility of the guidance and control scheme. Inspired by the Hera mission, this study explores the aforementioned aspects of the design of a formation for the exploration of the Didymos binary asteroid system, which comprises many complications but also challenges for many other future missions to fly in unexplored environments
Non-Uniform Gravity Field Model on Board Learning During Small Bodies Proximity Operations
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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