1,720,962 research outputs found
Virtual Mars Simulator for Rover Autonomy Validation and Testing
No full textThe paper presents a tool develop to provide a general purpose testbed to validate the design, to simulate and settle surface operations, to check for on-board autonomy performances within the wide field of planetary surface exploration missions. More specifically, attention is here focused on planetary rovers, a significant element of current and incoming space missions. To this end the develop simulation tool is made up of different sets of components to be activated and tailored according to the scenario to be analyzed and the tests to be run. The rover kinematics simulator, for instance, may be adequate to test the high level autonomy skills such as those related to the on board path-planning; on the other hand, the rover dynamics simulation module - which includes the soil-wheel interaction evaluation - may be exploited to test for the selected set of actuators. The tool is made of a simulation module and a virtual reality interface. In particular the virtual reality is exploited to generate commands sequencing, to check for the navigation and locomotion systems, and to visualize the results. The simulation module includes: a user defined rover configuration; a navigation module - based on a potential field techniques for obstacles avoidance - to let the vehicle safely move into the virtual environment created for the mission currently under study; the multi-body model of the rover nested in the simulation environment, including a wheel-soil interaction model; an artificial vision system to get a detailed reconstruction of the environment, the path-planner leans on to identify a safe path. The virtual environment contains all physical properties of the user defined planet surface; information about past missions are considered to model the rock distribution and the soil parameters; the tool exploits those inputs to build a soil map, that it is used by the navigation module to solve the path-planning problem. The rover simulator is a dynamic and complex project, but it is fundamental to get rid of a planetary surface vehicle robust design to successfully cope with uncertainties intrinsic with the space environment. More those uncertainties may give rise to unpredictable events only manageable through an enhanced on board autonomy a simulator helps to validate
Software Simulator for Robotic Exploration of the Lunar Surface
No full textValidation and verification are key points within a space project to check for reliability of the designed product. Of course, those phases are fundamental within the development of projects focused on planetary exploration too, such as those involving mobile elements on the surface; on board software, operations, and operational modes must be checked in a specific simulation environment, possibly including some software representation of the on board hardware too. A space mission simulator allows checking for the design robustness too, as different and complex faulty scenarios may be analysed either to revise the hardware solutions or to correctly define the reconfiguration procedures. Although spacecraft simulators are routine at control centers, rover virtual simulator is a young area for Europe as no space rover has been deployed yet. While the ExoMars program offers a great field for Martian applications, the Lunar Google XPrize challenge represents a perfect lunar scenario to start working on that topic: according to the challenge statement, a rover must be sent on the Moon within 2012, built exploiting only private sponsorships. Italy is running the race with the so called Team Italia: a mainly academic consortium supported by three important space involved national companies. To support the project, the Aerospace Engineering Department of Politecnico di Milano tailored an under development virtual simulator on the lunar mission scenario: at this early phase of the project the robustness of the sensorsarclhteeturc can be checked; to visualize the rover behaviour on the surface greatly helps the designers revising and refining the preliminary choices. Moreover, activity planning, operation sequences and operational modes can be easier defined and cross checked. The effects of a lot of faulty conditions may be analyzed to better understand how to cope with either through the design or during operational phases. The simulator here presented supplies: the representation of our satellite environment; orbital mechanics features to let the user identify the visibility windows between the rover antenna and a selected ground station on Earth; representation of the rover - user defined - according to the current design; a navigation module, to define the safe path according to the current map of the environment surrounding the rover; the multi-body model of the rover integrated in the simulation environment, including the traction control of the wheels. The drivers for designing the simulator architecture and selecting the implementation environment for the tool were the portability and the flexibility. The simulator, in fact, must provide a software framework for testing different levels of autonomy - plug-in of external modules and tools must be easy - simulated hardware must be simply redefineable to support the system design process; validation of different granularity of the mission plan shall be feasible The proposed tool merges a physic and a graphic (Irrlicht) engine. Irrlicht is a cross-platform high performance real-time 3D engine; it is a high level API for creating complete 3D and 2D applications like games or scientific visualizations. It comes with a wide documentation and integrates all the state-of-the-art features for visual representation like dynamic shadows, particle systems, character animation, indoor and outdoor technology. The engine is open source. The virtual environment contains all physical properties of the planetary surface, rock distribution and terrain properties, exploited to evaluate the interaction with the rover. The map of the soil properties is an output of the tool, the user can select the soil type, introducing the soil parameters or a predefined soil class; currently the data of Lunar and Martian surface are available, but the tool is highly flexible and configurable. The tool exploits those inputs to build the soil map. The navigation module solves the pathplanning problem by applying a potential field method, the target position attracts the rover while obstacles repulse it; therefore, the global effects on the rover, evaluated at each step, determines the future travelling direction. The rover simulator is going to be exploited by the Team Italia to check for rover operations feasibility and robustness both in nominal and possibly faulty scenarios and to validate the design before starting integrating the whole system. The paper will deeply describe the features of the proposed tool and will discuss open points and future refinements
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Rosetta Mission: On-Comet Operation Planning for the Sampler, Drill and Distribution Subsystem
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