Alunissage

Résumé

L’alunissage ou alunage est un néologisme désignant l'arrivée sans dommage d'un engin spatial habité ou inhabité sur la surface de la Lune. L'exploration de la Lune a été un des buts de l'humanité dès que celle-ci a compris que la Lune était le corps céleste le plus proche de la Terre. L'un des exemples les plus flagrants étant le fameux roman de Jules Verne, De la Terre à la Lune, écrit en 1865, ou plus récemment les albums de Hergé, Objectif Lune (1953) et On a marché sur la Lune (1954). Le premier véhicule qui s'est posé sur la Lune est la sonde Luna 9 envoyée par l'Union soviétique en 1966. La première arrivée d'un homme sur la Lune est celle de la mission américaine Apollo 11 commandée par Neil Armstrong, accompagné de Buzz Aldrin. Armstrong posa le module lunaire Eagle sur la surface de la lune à 20 h 17 min 40 s UTC (21 h 17, heure française), le . Un total de douze hommes ont atterri sur la Lune lors des différentes missions du programme Apollo, et en incluant les missions

Source officielle

https://fr.wikipedia.org/wiki/Alunissage

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An Adaptive Landing Gear for Extending the Operational Range of Helicopters

Tobias Löw

Conventional skid or wheel based helicopter landing gears severely limit off-field landing possibilities, which are crucial when operating in scenarios such as mountain rescue. In this context, slopes beyond 8° and small obstacles can already pose a substantial hazard. An adaptive landing gear is proposed to overcome these limitations. It consists of four legs with one degree of freedom each. The total weight was minimized to demonstrate economic practicability. This was achieved by an innovative actuation, composed of a parallel arrangement of motor and brake, which relieves the motor from large impact loads during hard landings. The loads are alleviated by a spring-damper system acting in series to the actuation. Each leg is individually force controlled for optimal load distribution on compliant ground and to avoid tipping. The operation of the legs is fully autonomous during the landing phase. A prototype was designed and successfully tested on an unmanned helicopter with a maximum take-off weight of 78 kg. Finally, the implementation of the landing gear concept on aircraft of various scales was discussed.

IEEE2019

Chargement

Low-energy Electron Holography Microscope for Imaging of Single Molecules

Sven Alexander Szilagyi

Structure determination techniques are an essential tool to investigate and understand molecules, especially in biology, where functionality crucially depends on structure. The dominant high-resolution methods, such as transmission electron microscopy and X-ray diffraction, rely on ensemble averaging, making them unsuitable for evidencing structural variations of flexible molecules. Common single-molecule imaging techniques like scanning probe microscopy achieve high resolution but lack access to 3D objects. A possible way to overcome these limitations is offered by low-energy electron holography (LEEH). So far, LEEH achieved molecular imaging at resolutions in the range of 7-8 Å on the single-molecule level. A resolution in the range of a few Å, which would give access to atomic details of molecular structures, is in theory attainable. Obtaining a resolution near the theoretical limit requires a fully optimized LEEH setup and workflow, for which in particular sample and emitter preparation are crucial. Here, I present a novel LEEH microscope with a unique experimental workflow, which is capable of resolving molecular substructures with an unprecedented resolution for LEEH experiments. The newly constructed LEEH microscope takes advantage of an efficient vibration isolation system and is remote-controlled to minimize external perturbations. The setup is capable of low-temperature (50 K) measurements, which enhances the stability of the system. A reliable way for preparing highly coherent electron emitters constituted by sharp tungsten tips is presented along with different methods for improving their performance via functionalization and UHV treatments. I show an optimized and reliable substrate preparation protocol resulting in ultra-clean free-standing single-layer graphene (SLG) samples. Native electrospray ion beam deposition (ES-IBD) allows for the transfer of non-volatile molecules from solution into gas phase and onto the substrate. By employing a quadrupole mass selection, highly pure molecular ion beams are obtained, which are soft-landed onto the SLG substrate in a controlled and reproducible manner while retaining an intact structure. This versatile preparation method allows us to study a great variety of molecules by LEEH. Data on proteins with masses ranging from 12-820 kDa reveal molecular shapes consistent with model structures. Locally, structural details as small as 5 Å were identified, thus we are approaching our goal of a resolution in the range of a few Å. The application of our methodology to flexible proteins, exemplified by antibodies, allowed for the imaging of their conformational variability and for determining the influence of the sample preparation on their structure. This gave us the possibility to directly image gas-phase related conformations. Data of compact molecular systems with masses below 3 kDa reveal that our LEEH microscope is able to investigate small molecules, such as porphyrines, at high imaging contrast. The presented results indicate that an optimized LEEH setup and workflow in combination with ES-IBD is a versatile microscopy method, which is filling the gap between high-resolution and single-molecule techniques by elucidating structural details of various molecular species.

EPFL2022

Chargement

Monolithic integrated circuits (ICs) have been miniaturized over the past five decades, and today their components range in size from hundreds of microns to several nanometers. Making point contact with electrical samples under a microscope is referred to as microprobing or nanoprobing and is carried out using micromanipulators equipped with sharply-ended probe needles. Probe landing on the sample is a critical step in this process since physical contact with the sample can damage the probe tip or the sample itself. Hence, this research was motivated primarily by the desire to find a novel method of monitoring and controlling physical contact between probe tip and sample, increasing its reliability in micro- and nanoprobing.Micro- and nanoprobing often involve qualified operators using microscope visual feedback to land the probe. This method, however, has several limitations, including a constrained field of view and no qualitative contact assessment. A more versatile solution is to measure the contact force between the probe tip and the sample since it does not rely on microscope images and provides an additional feedback channel that complements visual-servoing and facilitates micromanipulation. This work reviews a number of known methods of measuring force on a small scale, but none fully meets the needs of micro- and nanoprobing. The main challenges of these applications include, among others, measuring forces in the nanonewton to millinewton range, using different probe tips based on the type of sample, controlling contact force to obtain stable reliable conditions for electrical measurement, and protecting the probing system against excessive pressure exerted by the probe tip.The core objective of the thesis is to find a method for measuring and controlling the contact force between a probe tip and a sample that addresses the micro- and nanoprobing requirements. The proposed concept is based on a compliant mechanism that transduces the contact force applied to the probe tip into an output displacement. Through stiffness adjustment, the mechanism is capable of handling a wide range of forces that occur during micro- and nanoprobing. As a result of stiffness adjustment, the load cell can be designed at mescoscale, which provides high stiffness in transverse directions, and facilitates the interchangeability of probe tips. Using different probe tips necessitates analyzing gravity effects on the operation of the load cell and compensating for zero offset. Additionally, the study examines active force control implemented through stiffness and offset force adjustment, which provides a constant-force characteristic, bi-stable mode with overload protection, and allows fine probe tip positioning.Several polymer demonstrators and metal prototypes were fabricated as part of the work, allowing the experimental validation of subsequent stages. The performance of these mechanisms was compared with that of the analytical models and the finite element analysis developed within the research. The obtained results demonstrate the successful fulfillment of the requirements, including the ability to measure static contact forces over 60 mN with a resolution of 10nN (dynamic range of 6x10^6). A wide range of stiffness and offset force adjustments enable probe tip positioning with a resolution of 12 nm over a range of 5.64 mm. Finally, the new load cell was used for microprobing on a sample of micropillars to validate its different operating modes.

EPFL2022

Chargement

Low-energy Electron Holography Microscope for Imaging of Single Molecules

Sven Alexander Szilagyi

EPFL2022