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Guyancourt, France

Mandeville J.-C.,MANDESPACE | Perrin J.-M.,French National Center for Scientific Research | Perrin J.-M.,Laboratoire ATmospheres Milieux | Vidal L.,CNRS Mulhouse Institute of Materials Science
Acta Astronautica | Year: 2012

During the last three decades a wide variety of surfaces have been brought back to Earth after being exposed to space environment. The impact features found on these surfaces are used to evaluate the damages caused to spacecraft and can give clues to the characteristics of the orbital debris and meteoroids that created them. In order to derive more precisely the particle parameters and to improve the analysis of projectile remnants, we have performed an extensive analysis of craters caused by the impact of high velocity particles on thick ductile targets, using a micro-particle accelerator. We show that from the geometry of the craters and from the analysis of the remnants it is possible to derive the main characteristics of the projectiles. In particular, using up-to-date instrumentation, scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) spectrometer, we found that even small residues inside craters can be identified. However, this study shows that a velocity resolution better than 1. km/s would be appropriate to obtain a fair calibration of the impact processes on a ductile target. This would allow to decipher with precision impact features on ductile surfaces exposed to space environment. © 2012 Elsevier Ltd.


Mandeville J.-C.,MANDESPACE | Perrin J.-M.,French National Center for Scientific Research | Perrin J.-M.,Laboratoire ATmospheres Milieux | Vidal L.,CNRS Mulhouse Institute of Materials Science
Acta Astronautica | Year: 2012

During the last three decades a wide variety of surfaces have been brought back to Earth after being exposed to space environment. The impact features found on these surfaces are used to evaluate the damages caused to spacecraft and can give clues to the characteristics of the orbital debris and meteoroids that created them. In order to derive more precisely the particle parameters and to improve the analysis of projectile remnants, we have performed an extensive analysis of craters caused by the impact of high velocity particles on thick ductile targets, using a micro-particle accelerator. We show that from the geometry of the craters and from the analysis of the remnants it is possible to derive the main characteristics of the projectiles. In particular, using up-to-date instrumentation, scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) spectrometer, we found that even small residues inside craters can be identified. However, this study shows that a velocity resolution better than 1 km/s would be appropriate to obtain a fair calibration of the impact processes on a ductile target. This would allow to decipher with precision impact features on ductile surfaces exposed to space environment. © 2012 Elsevier Ltd.


Dupont J.-C.,Ecole Polytechnique - Palaiseau | Haeffelin M.,Ecole Polytechnique - Palaiseau | Protat A.,Laboratoire ATmospheres Milieux | Bouniol D.,Meteo - France | And 2 more authors.
Boundary-Layer Meteorology | Year: 2012

A suite of active and passive remote sensing instruments and in-situ sensors deployed at the SIRTA Observatory (Instrumented Site for Atmospheric Remote Sensing Research), near Paris, France, for a period of six months (October 2006-March 2007) document simultaneously radiative, microphysical and dynamic processes driving the continental-fog life cycle. The study focuses on a 6-day period between 23 and 29 December 2006 characterized by several stratus-cloud lowering and lifting events and almost 18 h of visibility below 1 km. Conceptual models and different possible scenarios are presented here to explain the formation, the development and the dissipation phases of three major stratus-fog events and to quantify the impact of each driving process. For example, slowly evolving large-scale conditions characterized by a slow continuous cloud-base lowering, followed by a rapid transient period conductive to fog formation and dissipation, are observed for cases 1 and 3. During this stable period, continuous cloud-top radiative cooling (≈ -160 Wm -2) induces a progressive and slow lowering of the cloud base: larger droplets at cloud top (cloud reflectivity approximately equals to -20 dBZ) induce slow droplet fall to and beyond cloud base (Doppler velocity ≈ -0.1 ms -1), cooling the sub-cloud layer by evaporation and lowering the saturation level to 100 m (case 1) or to the surface (cases 2 and 3). Suddenly, a significant increase in Doppler velocity magnitude ≈ -0.6 ms -1 and of turbulent kinetic energy dissipation rate around 10 -3 m 2s -3 occurs at cloud base (case 1). These larger cloud droplets reach the surface leading to fog formation over 1.5 h. The Doppler velocity continues to increase over the entire cloud depth with a maximum value of around -1 ms -1 due to the collection of fog droplets by the drizzle drops with high collection efficiency. As particles become larger, they fall to the ground and lead to fog dissipation. Hence, falling particles play a major role in both the formation and also in the dissipation of the fog. These roles co-exist and the balance is driven by the characteristics of the falling particles, such as the concentration of drizzle drops, the size distribution of drizzle drops compared to fog droplets, Doppler velocity and thermodynamic state close to the surface. © 2012 The Author(s).


Riviere E.D.,CNRS Molecular and Atmospheric Spectrometry Group | Pommerau J.-P.,Laboratoire ATmospheres Milieux | Amarouche N.,Division Technique Of Iinstitut National Des Science Of Lunivers | Ghysels M.,CNRS Molecular and Atmospheric Spectrometry Group | Cousin J.,CNRS Molecular and Atmospheric Spectrometry Group
European Space Agency, (Special Publication) ESA SP | Year: 2011

The entry of water vapour in the tropical stratosphere is still a highly debated issue but is crucial for the radiative and the chemical balance of the stratosphere. This entry is due to two competing processes, i) The slow ascent leading to dehydration at the global scale (so-called the cold trap) is said to mainly drive the water concentration at the tropical tropopause. ii) Overshooting convection, inject ice in the lower stratosphere leading to a potential hydration. It is a fast and local process, difficult to capture by global scale model. TRO-pico is a project funded by the French ANR dedicated to study the impact of tropical convective overshooting on stratospheric water budget from the local to wider scales. It is based on a small balloon campaign from Bauru, SP, Brazil at two timescales (overall wet season, and intense convective season), followed by the campaign data analysis with a wide set of modeling tools. Here we describe the scientific context of TRO-pico, the objectives of the project, the campaign planned to start in November 2011, as well as the instruments to be flown in Brazil, which have recently participated in the Kiruna 2011 campaign with preliminary results from this campaign.

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