1,720,965 research outputs found
Electric Propulsion System for a Maneuverable Orbital Vehicle
No full textThis paper presents a proposed maneuverable orbital vehicle based on the International Space Station (ISS) equipped with electric thrusters. The vehicle makes use of an external site of the ISS (e.g., the Express Pallet) to host a detachable platform which is able to perform a variety of missions, including formation flying with the ISS and missions to very low Earth orbit, down to 130 km altitude. After having accomplished a mission, the vehicle flies back to the ISS and rendez-vous in a semi-autonomuous mode to be refurbished and prepared for the next flight. The possible applications of such system include interferometric astronomy, the study of the extreme layers of the atmosphere, and high-resolution Earth imaging. The electric propulsion system features a cluster of high power Hall-effect thrusters, sized such as to give sufficient thrust authority to drive the vehicle without the need of chemical propulsion systems, yet able to be powered by standard deployable solar panels of acceptable extension. The vehicle is feasible with currently available electric propulsion and power generation systems
Low-Altitude Constellations for Remote Sensing
No full textWe present a constellation of three satellites capable of remote sensing operation at an orbital altitude as low as 297 km thanks to the use of an electric propulsion system for orbit maintenance. The mission architecture and the spacecraft configuration are such as to fit a multiple launch on a Vega small launcher. Orbit simulation is carried out using a proprietary code for low-thrust trajectory dynamics. Propellant mass and maneuver durations are computed for the main orbit control tasks and the system mass budget is evaluated for the payload, propulsion and power subsystems. We conclude that low-altitude remote sensing can be effectively and carried out with a constellation of three small spacecraft equipped with electric thruster, using present-day technology
FEEP Thruster Survivability in the LEO Atomic Oxygen Environment
No full textIn FEEP thrusters, field ionisation of propellant, usually cesium, occurs on the liquid metal surface at the outlet of a micrometric slit. Some concern was raised on the use of FEEP in low Earth orbit, since it was feared that the relatively high atomic oxygen concentration could provoke clogging of the slit due to cesium oxidation. To assess this potential failure mechanism we have investigated the FEEP thruster compatibility with a 200 km altitude atomic oxygen environment. In our experiment, a 50 mm slit, 1 mN FEEP thruster was exposed to direct impingement of atomic oxygen. Ion emission quality was monitored using scanning electrostatic probes. No significant degradation of the thruster performance was observed after as long as 384 hours total exposure to severe atomic oxygen flux and to an intense molecular oxygen background. It is concluded that the FEEP thruster can survive in a very low LEO environment without failures due to interaction with the residual atmosphere
Earth Observation from Elliptical Orbits with Very Low Altitude Perigee
Full text linkSmall Earth Observation satellites can obtain higher resolution with smaller payloads when operating at very low altitude. The life limiting effect of residual atmospheric drag can be reduced flying elliptical, low-altitude perigee orbits, with perigee right above the mission target; however, such orbits are severely affected by Earth gravitational field anisotropy and drag itself. The use of on-board electric propulsion enables this class of missions, making it possible to control and maintain orbital parameters without adding too much to the overall vehicle mass and size. This paper illustrates a possible validation mission for such a concept
Laser Powder Bed Fusion: A Review on the Design Constraints
Full text linkWith the creation of additive manufacturing production lines and the adoption of additive technologies, such as Laser Powder Bed Fusion, as standard manufacturing technologies for the mass production of parts, many considerations arise. In particular, product quality assurance is surely a very important aspect to be considered when talking about mass production. Laser powder bed fused parts are characterized by specific characteristics, such as quite rough surfaces and internal cavities filled with powder after the part construction. The need to ensure part quality and the importance to guarantee quality to all the parts made within the production line highlights the need to design the part addressing all the criticalities resulting from the manufacturing process, in addition to the ones related to the operative conditions. In this work, the attention is placed on two important topics: part surface inspectability and part cleaning. In particular, part inspectability is a crucial aspect in determining part coherence with design specifications. Part production via LPBF puts interpretability issues in inspecting the parts. Part cleaning is a crucial topic as well. Part cleaning is related to the design of the part to guarantee a correct powder evacuation from all the internal channels and cavities. Within the work, problems will be defined and design guidelines will be proposed to manage these topics
Comparative evaluation of fuzzy axiomatic design and IAMS comprehensive VIKOR approaches for material selection in mechanical design
Full text linkIn the mechanical design, the selection among material alternatives has become a pressing issue due to the progressive growth in the complexity of mechanical systems, in search of continuous increase in performance and the presence of a wide range of possible materials. Moreover, there are many requests for projects, and this makes the choice of material a decisive activity for the success or failure of the project itself. This paper makes a comparative evaluation of two important approaches to identify the best materials alternatives: The C-VIKOR and the Fuzzy Axiomatic Design. The work considers as a case study the selection of the material for the production of the valve seats in a high-performance engine. An evaluation of the results obtained is made to show the peculiarity of each of the two approaches
Technological and economical consideration for turbine blade tip restoration through metal deposition technologies
Full text linkIn the oil and gas industry, repair activities are critical to keep the maintenance costs of turbomachinery equipment down. Several repair technologies can be applied to various components of turbomachines. When dealing with gas turbines, the repair of turbine rotor blades has always been a very sensitive topic, given their critical application and their impact in terms of cost on the whole turbine lifecycle. Specifically, cracking and wearing of blade tips are some of the most common failure modes. Thus, the repair of these failure modes is of paramount importance, both for the original manufacturer as well as its aftermarket competitors. The present paper describes blade tip repair technologies from an original equipment manufacturer standpoint. Three different approaches are introduced and described for tip restoration. Laser cladding is presented first, since it is one of the most common technologies for this application, and then original equipment manufacturer which is currently being applied is presented. Then, cold metal transfer and direct metal laser melting technologies are investigated. A technologic and financial assessment is made to drive the technology selection for the turbine blades restoration
Surveillance Constellations of Low Altitude Small Satellites with Electric Propulsion
No full textSmall spacecraft may carry out surveillance of crisis areas in an effective way when deployed in constellations. In order to limit cost, small spacecraft shall operate at low orbital altitude, so as to use small and relatively unexpensive optical payloads. We show that extended operation in low LEO is made possible by the use of electric propulsion for atmospheric drag compensation. Mission performance is discussed with reference to utilization for the surveillance of a Mediterranean/Middle East region with an extended mission target lifetime of up to 8 years. The constellation design and the overall spacecraft arrangement are presented, as well as the electric propulsion subsystem, based on the HT100 Hall thruster by Alta
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