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 ICAPS experiment and light scattering measurements
ICAPS (Interactions in Cosmic and Atmospheric Particle Systems) is an international scientific programme for measurements under microgravity conditions. This ESA fundamental physics project (now in phase B) should be operational on board the ISS in 2008. A precursor instrument I2SP (Impact Icaps Science Precursor) will operate from 2006.
[logo icaps]
Light scattering measurements, scientific objectives
[phase functions]
 [dependance]
 [aggregates]

Example of a scientific objective: infer from cometary polarimetric phase functions and from their wavelength dependence the physical properties of the light scattering aggregates.
Light scattering measurements with ICAPS allow the monitoring of the brightness and polarization of the light scattered by dust particles, and by the aggregates and regoliths that they progressively form. Such measurements indeed require microgravity conditions to avoid particles sedimentation, and long duration experiments to allow the formation of structural analogues of natural aggregates and regoliths. It is then possible to:
• Deduce, without any ambiguity, the physical properties (morphology, size distribution, porosity…) of some natural media (atmospheric aerosols, cometary dust, regoliths, interplanetary dust cloud, circumstellar disks…) from observations of the solar or stellar light they scatter.
• Validate light scattering codes for irregular aggregates of dust particles and regoliths, with special emphasis on the exploration of the backscattering region.

Light scattering unit, instrumental concept

The experimental feasibility was tested through light scattering measurements performed in the laboratory and during numerous parabolic flight campaigns with PROGRA2. It relies on the technical heritage of the light scattering experiment (built at Service d’Aéronomie) for the European sounding rocket instrument CODAG-SRE.
The unit (under development at Service d'Aéronomie and ULB) is along an equatorial ring inserted on the wall of the experimental chambers (where the aggregation processes are taking place). Through about 25 vacuum-tight optical windows (corresponding to phase angles ranging from the near backscattering region to 170°), it allows the simultaneous determination of the brightness and polarization phase curves in three wavelengths (blue, red, near infrared), as well as the retrieval of the Stokes parameters leading to a better knowledge of the interactions between the grains building an aggregate and of the multiple scattering phenomena.
[instrumental principle]

Instrumental principle of the light scattering unit, with the     analysers mounted on a ring around the agglomeration chamber

References
  • A.C. Levasseur-Regourd, M. Cabane, V. Haudebourg, J.C. Worms, Light scattering experiments under microgravity conditions, Earth, Moon, Planets, 80, 343-368, 1998
  • A.C. Levasseur-Regourd, M. Cabane, E. Chassefière, V. Haudebourg, J.C. Worms, The CODAG Light Scattering Experiment for light scattering measurements by dust particles and their aggregates, Adv. Space Res., 23, 7, p. 1271-1277, 1999
  • J.C. Worms, J.B. Renard, E. Hadamcik, A.C. Levasseur-Regourd, J.F. Gayet, Results of the PROGRA2 experiment: an experimental study in microgravity of scattered polarised light by dust particles with large size parameter, Icarus, 142, 1, p. 281-297, 1999
  • J.C. Worms, J.B. Renard, E. Hadamcik, N. Brun-Huret, A.C. Levasseur-Regourd, The PROGRA2 light scattering instrument, Planet. Space Sci., 48, 493-505, 2000
  • E. Hadamcik, J.B. Renard, J.C. Worms, A.C. Levasseur-Regourd, M. Masson, Polarization of light scattered by fluffy particles (PROGRA2 experiment), Icarus, 155, 497-508, 2002
  • E. Hadamcik, J.B. Renard, A.C. Levasseur-Regourd, J.C. Worms, Polarimetric study of levitating dust aggregates with the PROGRA2 experiment, Plan. Space Sci., 50, 895-901, 2002
  • A.C. Levasseur-Regourd, E. Hadamcik, Light scattering by irregular dust particles in the solar system: observations and interpretation by laboratory measurements, J. Quant. Spectros. Radiat. Transfer, 79-80, 903-910, 2003
  • E. Hadamcik, J.B. Renard, A.C. Levasseur-Regourd, J.C. Worms, Relevance of laboratory light scattering measurements on natural particles with the PROGRA2 experiment, J. Quant. Spectros. Radiat. Transfer, 79-80, 679-693, 2003
  • A.C. Levasseur-Regourd, Cosmic dust physical properties and the ICAPS facility on board the ISS, Adv. Space Res., 31/12, 2599-2606, 2003
Useful links
ICAPS  
ICAPS CRT-5
ESA ICAPS  
PROGRA2  
Novespace

Service d'aéronomie: updated: 06/23/2004
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