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Automated Service Vehicle for ISS Surveying (ASVIS)
Study Context
The ASVIS study has been performed by SENER (E) as prime contractor and GMV (E) as sub-contractor. The study is part of the STEP programme. The Modelling and Simulation section at Estec has been providing inputs and support to this study in the area of the real-time test bench and the 3D visualisation.  
ASVIS inspector vehicle
ASVIS Description
The Automated Service Vehicle for ISS Surveying (ASVIS) is based on an unmanned vehicle operating outside the ISS. ASVIS starts its missions from an external Base Platform available for external payloads. ASVIS is an operative system designed for providing services to the ISS like: inspection at different ranges (both periodical and on-demand) and support to EVA. The maximum duration of each mission for the autonomous vehicle is 10 hours and the frequency of the missions is twice per month during a 10 years lifetime. Once the autonomous vehicle is docked at the Base Platform, some maintenance operations are performed: battery recharging, tanks refuelling (propulsion is based on nitrogen) and software updates. The Base Platform hosts a Cold Gas Storage system and Solar cells in order to provide all the required power and the fuel ASVIS needs. In addition, a Monitoring and Control System (MCS) is located inside the ISS for controlling the whole system, action performed by an IVA crewmember. A Ground Monitoring and Control System (GMCS) has also been defined.
ASVIS test bench
GNC Validation
The Guidance, Navigation and Control (GNC) algorithms validation has been performed in two steps. First, a simulator called ASMIS has been developed in the Matlab/Simulink environment, including all features like on board processor (implementing the Mission and Vehicle Management tasks, GNC algorithms and Failure Detection and Isolation functions), Dynamic and Kinematics Equations, sensors and actuators models, communications (with ground and ISS), ISS models and measurements, system database and introduction of off-nominal conditions. A full test campaign was performed using ASMIS, demonstrating the validity of the proposed GNC concept. The second step of the validation process is the migration of the Simulink simulator to the EuroSim/Linux environment. GNC algorithms are implemented in a target platform, which is controlled and operated from a laptop. Mathworks Embedded Coder and GNU cross compilers have been used for this translation. The Real World models are directly implemented in the laptop running on EuroSim using Real Time Workshop and Mosaic for its conversion to EuroSim from Simulink models. A user-friendly Man Machine Interface has been implemented for managing the overall procedure –including both EuroSim environment and target platform handling– avoiding all the hand written modifications in the generated code and creating automatically the necessary interfaces with the corresponding device drivers.
ASVIS docked
3D Visualisation
In addition to the validation activities, a 3D Visualisation tool has been developed in collaboration with ESA, fed by the EuroSim output data, improving the validation of the designed concept. CATIA models of the ASVIS system (vehicle and base platform) were converted to VRML format and integrated in a single tool with ISS models developed by ESA. Specific add-ons are shown during the simulation like antennae and cameras field of views, thruster activations, unit failures, position and illumination lights, proximity sensor beams, etc.
Last update: 20 September 2006

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