1,720,992 research outputs found
Miniature docking mechanism for CubeSats
No full textThis paper presents the design and characterization of a miniature docking mechanism for nanosatellites. Potential applications are several, including servicing of orbital vehicles (e.g. refuelling, components replacement, deorbiting or reboosting) and assembly of large structures (e.g. telescopes, antennas). The mechanism responds to the constant demand of enabling technologies from the booming small satellites market. The developed system has a traditional probe–drogue configuration; it is equipped with a sensor to detect contact and a single servo-actuator to lock the connection. The simple, though effective, design fills a relevant gap in the field of nanosatellite technologies. Numerical simulations have been conducted to evaluate the dynamics of docking procedures and to estimate loads exchanged at contact. Experimental results validate the simulations and prove the high tolerance to angular and linear (lateral) misalignment
1 kHz remote control of a balancing robot with Wi-Fi-in-the-loop
No full textCountless industrial applications can potentially benefit from the implementation of wireless control systems, leading to a widespread research effort to investigate new solutions in the field. Nevertheless, currently available wireless communication standards for industrial automation are not able to achieve high control frequencies. In particular, time-critical applications (e.g. industrial robotics and manipulation) require high sampling frequencies to be properly implemented. The higher throughput provided by IEEE 802.11 (Wi-Fi) can theoretically tame critical applications, although reliability is a key issue. In this work Wi-Fi is adopted to increase the achievable control rates up to 1 kHz, while reliability is guaranteed by mitigating communication flaws through model-based estimation techniques. The core of the proposed approach relies on a modified Kalman filter that exploits a buffer of incoming measures to account for delayed data packets. The proposed solution is validated through a hardware-in-the-loop experiment that features actual Wi-Fi hardware and a commercial embedded PC board. The obtained results give a preliminary, yet valuable, validation of the proposed approach testing the solution on relevant hardware
Docking mechanisms for nano and micro satellites
No full textAt today, few mating technologies for nano and micro satellites have been designed and tested in relevant environment, despite the raising interest in making such platforms able to join, separate and independently reconfigure. In this framework, this paper presents a review of the research activities carried out in the last five years at the University of Padova with respect to small satellites docking mechanisms.
Research in this field began with the projects ARCADE project (Autonomous Rendezvous, Control And Docking Experiment) and its re-flight ARCADE-R2, that made it possible to develop and test a small-scale gender-mate mechanism inspired by Soyuz and ATV docking systems. As a concurrent solution to the ARCADE probe-drogue configuration, the concept of semi-androgyny was then proposed, consisting in a hybrid docking port that can act both as probe and drogue thanks to its shape-shifting capability: to perform mating, one of the two identical interfaces is actuated to change its shape in "drogue", in order to wrap around the other one creating the solid joint. Furthermore, two different working prototypes were developed to further investigate power, data and fluid transmission. In parallel, the results collected by ARCADE flights were employed in the design of a docking and recharging system for small drones
Time-Critical Wireless Networked Embedded Systems: Feasibility and Experimental Assessment
Full text linkIn this article, we investigate an innovative solution, to implement high sampling frequency industrial control by means of networked embedded systems connected via WiFi. The basic idea relies on a co-design approach for the control application, which is then able to adapt its sampling period, as well as to tune the Wi-Fi parameters, according to the feedback coming from the network. To this end, we implemented a cross-layer architecture acting at both application and data-link layers, which features a robust frame-delay state estimator, a time-efficient communication policy, and a specific tuning of the critical protocol parameters. Suitable hardware-in-the-loop experiments have been carried out exploiting two different embedded systems available off-the-shelf. The preliminary results, obtained from an extensive experimental campaign, are encouraging since they show that the proposed architecture enables industrial control applications requiring a sampling rate up to 1000 Hz, even in presence of communication impairments
Acquisition analysis for small-satellite optical crosslinks
No full textSmall satellites are increasingly exploited for the realization of low Earth orbit (LEO) constellations for Earth imaging, global connectivity and data relay. Optical crosslinks between satellites can drastically increase the constellation capability to transmit data to ground stations with reduced latency and increased total throughput. One critical aspect of optical crosslink is the acquisition phase, which requires that each satellite scans its field of view looking for the beacon laser transmitted by the partner terminal before starting communication. In this paper, the problem of beacon acquisition for optical crosslinks is analyzed, with focus on the small satellite case. Numerical simulations and a simplified, yet representative laboratory experiment are carried out to evaluate and compare two different scanning techniques quantitatively
Characterization of a new positioning sensor for space capture
No full textSpace missions that focus on On-Orbit-Servicing often involve the capture of a target satellite or space debris as a key event in the operational sequence. Space robots are among the most promising technologies to perform this task and mission architectures involving manipulators proved successful in orbit. Such mission scenarios are complex and imply a considerable risk of collision between the chaser and the target vehicles. For the sake of safety, it is of key importance to accurately position the capture interface w.r.t. the gripping point on the target, especially when relative distance is very low. During these phases, the guidance and control algorithms rely on pose measurements provided by navigation sensors that are generally able to reconstruct the target position and orientation only up to a certain distance between the camera and the target. To the purpose of having a complete control of the capture interface until contact, a new sensor based on a LED and a matrix of phototransistors has been developed. This paper describes the sensor and provides its preliminary characterization. A simple theoretical description of the sensor behavior is obtained from geometrical considerations, while experiments have been performed to measure the performances of the actual hardware implementation of the system
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