Papers by Thomas-louis Lophem
ESA Parabolic Flights, Drop Tower and Centrifuge Opportunities for University Students
“Fly Your Thesis!—An Astronaut Experience” is an educational programme launched by the ESA Educat... more “Fly Your Thesis!—An Astronaut Experience” is an educational programme launched by the ESA Education Office that aims to offer to European students the unique opportunity to design, build, and eventually fly, a scientific experiment as part of their Master or Ph.D. thesis. Selected teams accompany their experiments onboard the Zero-G aircraft for a series of three flights, each consisting of
Publisher’s Note: Granular Convection in Microgravity [Phys. Rev. Lett. <span xmlns:xlink="http://www.w3.org/1999/xlink" style="font-weight: bold;">110</span>, 018307 (2013)]
Physical Review Letters, 2013
Physical Review Letters, 2013
We investigate the role of gravity on convection in a dense granular shear flow. Using a microgra... more We investigate the role of gravity on convection in a dense granular shear flow. Using a microgravity-modified Taylor-Couette shear cell under the conditions of parabolic flight microgravity, we demonstrate experimentally that secondary, convective-like flows in a sheared granular material are close to zero in microgravity, and enhanced under high gravity conditions, though the primary flow fields are unaffected by gravity. We suggest that gravity tunes the frictional particle-particle and particle-wall interactions, which have been proposed to drive the secondary flow. In addition, the degree of plastic deformation increases with increasing gravitational forces, supporting the notion that friction is the ultimate cause.
Monthly Notices of the Royal Astronomical Society, 2013
Despite their very low surface gravities, the surfaces of asteroids and comets are covered by gra... more Despite their very low surface gravities, the surfaces of asteroids and comets are covered by granular materials -regolith -that can range from a fine dust to a gravellike structure of varying depths. Understanding the dynamics of granular materials is, therefore, vital for the interpretation of the surface geology of these small bodies and is also critical for the design and/or operations of any device planned to interact with their surfaces. We present the first measurements of transient weakening of granular material after shear reversal in microgravity as well as a summary of experimental results recently published in other journals, which may have important implications for small-body surfaces. Our results suggest that the force contact network within a granular material may be weaker in microgravity, although the influence of any change in the contact network is felt by the granular material over much larger distances. This could mean that small body surfaces are even more unstable than previously imagined. However, our results also indicate that the consequences of, e.g., a meteorite impact or a spacecraft landing, may be very different depending on the impact angle and location, and depending on the prior history of the small body surface.
Granular Matter, 2013
Despite their very low surface gravities, asteroids exhibit a number of different geological proc... more Despite their very low surface gravities, asteroids exhibit a number of different geological processes involving granular matter. Understanding the response of this granular material subject to external forces in microgravity conditions is vital to the design of a successful asteroid sub-surface sampling mechanism, and in the interpretation of the fascinating geology on an asteroid.
The dynamics of granular materials are involved in the evolution of solid planets and small bodie... more The dynamics of granular materials are involved in the evolution of solid planets and small bodies in our Solar System, whose surfaces are generally covered with regolith. An understanding of granular dynamics appears also to be critical for the design and/or operations of landers, sampling devices and rovers to be included in space missions. The AstEx experiment uses a microgravity modified Taylor-Couette shear cell to investigate granular motion caused by shear and shear reversal forces under the microgravity conditions of parabolic flight. The results will lead to a greater understanding of the mechanical response of granular materials subject to external forces in varying gravitational environments.
Numerical and Laboratory Investigations of Regolith Dynamics
Surfaces of planets and small bodies in our Solar System are often covered by a layer of granular... more Surfaces of planets and small bodies in our Solar System are often covered by a layer of granular material that can range from a fine regolith to a gravel-like structure of varying depths. Therefore, the dynamics of granular materials is involved in many events occurring during planetary and small-body evolution and contributes to their geological properties. However from planets to
AstEx is a microgravity experiment selected to fly on ESA's 51st Microgravity Research Campaign i... more AstEx is a microgravity experiment selected to fly on ESA's 51st Microgravity Research Campaign in November 2009. The experiment will investigate the dynamics of regolith on asteroid surfaces. Despite their very low surface gravities, asteroids exhibit a number of different geological processes involving granular matter. Understanding the mechanical response of this granular material subject to external forces in microgravity conditions is vital to the design of a successful asteroid sub-surface sampling mechanism, and in the interpretation of the fascinating geology on an asteroid. The AstEx experiment uses a microgravity modified Taylor-Couette shear cell to investigate granular flow caused by shear forces under the conditions of parabolic flight microgravity. It is intended to determine how a steady state granular flow is achieved in microgravity conditions, and what effect prior shear history has on the timescales involved in initiating a steady state flow in a granular material. Presented are the technical details of the AstEx experimental design with particular emphasis on how the team have designed the equipment specifically for the parabolic flight microgravity environment.
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Papers by Thomas-louis Lophem