ADVANCED MANUFACTURING METHODS FOR SYSTEMS OF MICROSYSTEM NANOSPACECRAFT – STATUS OF THE PROJECT

In the frame of an ESA TRP project, CSL, SIRRIS, ALMASpace and TAS-F associated to evaluate advanced manufacturing methods for application to space hardware. The state of the art of the new manufacturing methods, including additive manufacturing but also advanced bonding, joining and shaping techniques has been reviewed. Then three types of case studies have been developed successively. The first type was a re- manufacture of an existing piece of hardware using advanced techniques to evaluate if there is some potential improvement to be achieved (cost, production time, complexity reduction). The second level was to design and manufacture a part based on the application requirements. The last level was to design and manufacture a part taking into account the subsystem to which it belongs. All case studies have been tested in terms of achieved performances and resistance to the mechanical and thermal environment

New applications of Advanced Manufacturing Methods for space instrumentation and Systems of Nanospacecraft

In the frame of an ESA TRP project, our consortium has investigated the possibility to use advanced manufacturing methods for application to space hardware. After a review of the state of the art of the new manufacturing methods, including additive manufacturing but also advanced bonding, joining and shaping techniques, several case studies have been realized. These new techniques imply a different approach already at the design phase since the manufacturing constraints can be completely different. The goal of the project was to evaluate the different technologies from the design to the realization and learn how the classical design and development of such parts shall be adapted to take into account the different specificities of the new techniques. Three types of case studies have been developed successively. The first type was a re-manufacture of an existing piece of hardware using advanced techniques to evaluate if there is some potential improvement to be achieved (cost, production time, complexity reduction). The second level was to design and manufacture a part based on the application requirements. The last level was to design and manufacture a part taking into account in addition the subsystem to which it belongs. All case studies have been tested in terms of achieved performances and resistance to the mechanical and thermal environment. For each level, several case studies were proposed by ALMASpace and TAS-F and a pre-selection was performed to verify the feasibility and the interest of the proposed part for the project. For the first 2 levels, the 2 selected case studies have been designed, built and tested. A single case study was built for last level. The cases studies of level one were an aluminium inertial wheel housing (using electron beam welding to connect simple machined parts) and a mechanism housing fully made by additive manufacturing (electron beam melting of Titanium). The ones of level two were an aluminium tray for nanosatellite structure (assembled by salt dip brazing) and an antenna support bracket (designed by topological optimization and manufactured by laser beam melting of aluminium). The third level case study is a Sun Sensor for nanosatellite designed by topological optimization and including electronic circuit (optical detector and proximity electronic) deposited by aerosol jet printing directly on the aluminium structure. All case studies have been manufactured and tested and all part manufactured, despite including some imperfections, fulfilled all performance requirements

Electrical resistivity measured by millisecond pulse-heating in comparison to thermal conductivity of the stainless steel AISI 316 L at elevated temperature

Electrical resistivity of stainless steel AISI 316 L was measured by millisecond pulse-heating in the temperature range from room temperature to the melting point at approximately 1400°C. The measurement results of electrical resistivity as a function of specific enthalpy were combined with results of specific heat capacity measurements by differential-scanning calorimetry to obtain the relation between resistivity and temperature. Additionally to electrical resistivity and specific heat capacity, thermal diffusivity, density at room temperature, and thermal expansion were measured. From these results, thermal conductivity was calculated. Using the results of thermal conductivity and electrical resistivity, a Smith-Palmer-plot was drawn. It shows a significant deviation from the Wiedemann-Franz law with the Sommerfeld value due to the lattice component, electron scattering by solute atoms, and other smaller contributions

ABOUT THE DEMISABILITY OF PROPELLANT TANKS DURING ATMOSPHERIC RE-ENTRY FROM LEO

The concern about the on-ground risk caused by spacecraft fragments surviving atmospheric re-entry has significantly grown during the past decade, resulting in numerous activities of the space community like re-entry simulation tool development, improvement, and validation, as well as research for design-for-demise (D4D). The purpose of the first group is to increase the confidence in numerical re-entry risk predictions, while the second activity aims to develop new spacecraft design techniques which are likely to improve the demise behavior significantly. Standard (Titanium) propellant tanks for LEO (Low Earth Orbit) missions appear regularly within the group of spacecraft (satellite) components causing the highest on-ground risk, i.e. in the order of 20% for a 1-ton class Earth observation satellite. Thus, tanks are one of the primary targets for any D4D activity. Various ideas for demisable propellant tank concepts have been published recently, including aluminum tanks (e.g. based on aluminum-lithium alloys) or composite tanks (e.g. Carbon-fiber overwrapped metallic liners). The demonstration of the actual demisability of such new tank concepts has turned out to be difficult, sometimes even questionable. Intensive laboratory tests in arc-jet heated or plasma wind-tunnels and laser facilities have provided extensive results. Numerical simulations have been conducted to reproduce these experimental findings. This paper will contain a critical review of the latest experimental and numerical results about the demisability of satellite propellant tanks during atmospheric re-entry from LEO

Demisability assessment of space materials

Since March 2014, all ESA satellites and launcher upper stages which will be disposed of by atmospheric re-entry at the end of their operational life must demonstrate that the risk from fragments surviving the re-entry and causing casualties on ground is less than 1 in 10,000. This casualty risk is calculated by re-entry tools simulating the uncontrolled re-entry event using a computer aided design model of the spacecraft. The uncertainties on several parameters such as the aerothermodynamics fluxes model, the structural interfaces model, the materials model, and the level of detail of the spacecraft architecture will have an impact on the re-entry event simulation and the associated casualty risk calculations. To better understand the uncertainties associated to material modelling, five materials often used on space missions were tested in Plasma Wind Tunnels, mimicking atmospheric re-entry environment. Thermo-physical properties, thermo-optical properties and mechanical properties at high temperature were also characterized. Analysis of the samples after plasma wind tunnel tests was performed. A database compiling the materials properties measured and the plasma wind tunnel test results was created. The material properties characterised and generated during the activities will serve as inputs for the re-entry simulation events at equipment and system level

Fantasmagories du Moyen Âge

Arthur et ses chevaliers de la Table Ronde, Tristan et Yseut, mais aussi Jeanne d'Arc et Charles VII, le poète Villon sont autant de figures du passé médiéval dans lesquelles se reconnaît notre époque. Cet âge reculé se révèle être une source privilégiée d'inspiration avec laquelle les artistes engagent une relation à chaque fois renouvelée. Ainsi en est-il de la littérature des XIXe et XXe siècles, du Romantisme à l'Oulipo et en particulier la fantasy sous l'ombre tutélaire du grand Tolkien. Les supports d'un nouvel imaginaire médiéval sont multiples et fertiles, qu'il s'agisse de l'illustration inspirée de l'art des manuscrits, des études historiques scientifiques aux élucubrations fantaisistes et ésotériques. La chanson contemporaine, l'agencement des jardins ou bien les jeux de rôles, ces univers actuels nous proposent un jeu de miroir avec l'époque médiévale. Ce livre nous invite à un étrange et fécond dialogue entre les siècles