Simulations of the solar orbiter spacecraft interactions with the solar wind: effects on RPW and SWA/EAS measurements

International audienceWe present numerical simulations of the future Solar Orbiter spacecraft/plasma interactions performed with the Spacecraft Plasma Interaction System (SPIS) software. This spacecraft, to be launched in October 2018, is dedicated to the Sun observation with in-situ and remote sensing instruments, brought as close as 0.28 A.U. from our star. In this hot and dense environment, the entire satellite will be submitted to high radiations and temperatures (up to 10 Solar constants). Material responses to environment constraints (heat, U.V. flux, photoemission, secondary electron emission under electron impact – SEEE – or under proton impact - SEEP) might bias the scientific instrument measurements. Our interest is focused on two instruments: the Radio and Plasma Waves (RPW) and the Electron Analyzer System (EAS)

Extension of SPIS to simulate dust electrostatic charging, transport and contamination of lunar probes

A modification of the Spacecraft Plasma Interaction Software has been undertaken under ESA contract 4000107327/12/NL/AK (SPIS-DUST). The primary goal is to provide mission designers with an engineering tool capable of predicting charged dust behavior in a given plasma environment involving a spacecraft / exploration unit in contact with complex topological features at various locations of the Moon’s surface. The tool also aims at facilitating dust contamination diagnostics for sensitive surfaces such as sensors optics, solar panels, thermal interfaces, etc. In this paper, the new user interface and the new numerical solvers developed in the frame of this project is presented. The pre-processing includes the building of a 3D lunar surface from a topology description (i.e. a point list), an interface to position the spacecraft and a merging interface for the spacecraft elements in contact with the lunar surface. Concerning the physical models, the new solvers have been developed in order to model the physics of the ejection of the dust from the soils, the dusts charging and transport in volume and the dust interaction and contamination of the spacecraft. The post-processing includes the standard outputs of SPIS for the electrostatic computation and the plasma plus dedicated instruments for the diagnosis of the dusts. A set of verification test cases are presented in order to demonstrate the new capabilities of this version of SPIS in realistic conditions

New SPIS capabilities to simulate dust electrostatic charging, transport, and contamination of lunar probes

The spacecraft-plasma interaction simulator has been improved to allow for the simulation of lunar and asteroid dust emission, transport, deposition, and interaction with a spacecraft on or close to the lunar surface. The physics of dust charging and of the forces that they are subject to has been carefully implemented in the code. It is both a tool to address the risks faced by lunar probes on the surface and a tool to study the dust transport physics. We hereby present the details of the physics that has been implemented in the code as well as the interface improvements that allow for a user-friendly insertion of the lunar topology and of the lander in the simulation domain. A realistic case is presented that highlights the capabilities of the code as well as some general results about the interaction between a probe and a dusty environment

NGF Causes TrkA to Specifically Attract Microtubules to Lipid Rafts

Membrane protein sorting is mediated by interactions between proteins and lipids. One mechanism that contributes to sorting involves patches of lipids, termed lipid rafts, which are different from their surroundings in lipid and protein composition. Although the nerve growth factor (NGF) receptors, TrkA and p75NTR collaborate with each other at the plasma membrane to bind NGF, these two receptors are endocytosed separately and activate different cellular responses. We hypothesized that receptor localization in membrane rafts may play a role in endocytic sorting. TrkA and p75NTR both reside in detergent-resistant membranes (DRMs), yet they responded differently to a variety of conditions. The ganglioside, GM1, caused increased association of NGF, TrkA, and microtubules with DRMs, but a decrease in p75NTR. When microtubules were induced to polymerize and attach to DRMs by in vitro reactions, TrkA, but not p75NTR, was bound to microtubules in DRMs and in a detergent-resistant endosomal fraction. NGF enhanced the interaction between TrkA and microtubules in DRMs, yet tyrosine phosphorylated TrkA was entirely absent in DRMs under conditions where activated TrkA was detected in detergent-sensitive membranes and endosomes. These data indicate that TrkA and p75NTR partition into membrane rafts by different mechanisms, and that the fraction of TrkA that associates with DRMs is internalized but does not directly form signaling endosomes. Rather, by attracting microtubules to lipid rafts, TrkA may mediate other processes such as axon guidance

Measurement of energetic efficiency of electron emission under low energy electron beam irradiation: application to Hall thruster dielectric walls

International audienceFrom its discovery until nowadays, electrons emission (EE) has been thoroughly studied and has allowed numerous technologies development. Among them, RADAR, Scanning Electron Microscope and scintillators can be quoted. EE can also be a parasitic phenomenon especially for space applications (multipactor effect in wave guides, spacecraft charging, etc.). Until now, EE has essentially been described for high incident energy (superior to 100 eV). However several technologies are being developed which involved EE with low incident energy (below 100 eV). One of them is plasma thrusters for satellites applications. Toward this work, low energy EE impact (below 100 eV) on energetic balance in Stationary Plasma Thrusters (SPTs) will be discussed as well as method of measurement of this impact

Experimental investigation about energy balance of electron emission from materials under electron impacts at low energy: application to silver, graphite and SiO2

International audienceThe energy balance measurement of electron emission at a wall submitted to electron impact at low incident energy is a topic of interest for miscellaneous technological applications. This article points out the experimental protocol, biases corrections and post-process needed to obtain reproducible and quantitative electron emission measurements. The measurements have been performed for incident electrons energy between 5 eV and 105 eV and for three samples materials: silver, graphite and SiO 2. These measurements show that wall absorbs more energy at high incident electrons energy and that graphite absorbs more energy than silver, than SiO 2. Results are presented for mono-energetic incident electron beam and for a Lambertian energy distribution. Analytical laws fitted from experimental results and applicable for modelling issue are proposed for a Lambertian distribution of incident electrons

Study and Simulation of Low Energy Plasma Measurement on Solar Orbiter

International audienceThe flux of particles collected by scientific low energy detectors are sensitive to absolute and differential potentials, and may include both ambient and secondary particles emitted by the spacecraft itself. This work presents numerical models of particle detector behaviour on Solar Orbiter, using the SPIS software. The results presented in this paper show the necessity to take into account the spacecraft plasma interactions at the earlier stage of scientific missions' definition, as well as during measurement interpretation. It demonstrates that electrons emitted in the vicinity of the detectors may be the main contributor to low energy electron measurements pollution

Functional studies and cellular distribution of the F3 GPI-anchored adhesion molecule

Many adhesion molecules of the immunoglobulin superfamily expressed in the nervous system are attached to the neuronal membrane by a glycan-phosphatidylinositol. Using neuronal glycoprotein F3 as a model we will discuss how this lipid modification might confer on molecules specific properties which may be particularly well suited to a role in modulating neuronal interactions. In particular, the following data dealing with the question of how the glycosylphosphatidylinositol (GPI) anchor influences the function, transport and localization of this molecule will be presented. 1) When anchored to the plasma membrane, F3 fulfills the operational criteria of an adhesion molecule while its soluble form is able to stimulate neurite outgrowth of sensory neurons in culture. 2) In the hypothalamo-hypophyseal system, immunoblot analysis indicates that there is more F3 in the neurohypophysis where secretory axons terminate than in the hypothalamic nuclei where the molecule is synthesized. In addition, GPI-linked forms predominate in the nuclei while there are mainly soluble forms in the neurohypophysis, suggesting that there is conversion of the GPI-bearing form to the soluble form during axonal transport. 3) In the cerebellum, F3 is polarized to the tips of the axons of granule cells, the major neuronal population in this system, as an indication that indeed GPI might be a signal for targeting molecules to axons. However, some neurons such as Golgi cells express F3 over all their surface