1. INTERACTIONS What is regolith ? Dust particles cover the surfaces of asteroids, and of some planets and satellites. ICAPS will build simulated regoliths by forming thick and fluffy dust layers in microgravity, and study their optical, mechanical, thermal and electrical properties.APPLICATIONS Aeronomy Through a fuller understanding of terrestrial clouds, we can improve our knowledge of aerosols and clouds in the atmosphere of other Earth-like planets. Aerosol technology ICAPS could help to improve aerosol technology for industries like pharmaceuticals and dye producers. Materials Due to their non-dense structure, the surface to volume ratio of fractal aggregates increase to very large values, compared to usual bulk matter. Such novel materials (for, e.g. superconductivity, catalytic components, ceramics design) can be investigated with ICAPS. Fractal aggregate formation can help studying fractals as a “new” state of matter. Paper industry Light scattering studies have recently been applied to industrial products such as pigment, paper and paint to increase their whiteness whilst using smaller amounts of material. Light scattering studies from ICAPS will assist in these, and future industrial light scattering applications. Particle sizing Comparisons between the results from ICAPS experiments and theoretical models will help refine diagnostic tools for industrial particle sizing. Pollution removal Studying aerosol processes with ICAPS, such as scavenging processes in clouds and precipitation, could help to develop better abatement strategies and cleaning devices for nuclear and conventional industries. Weather and climate With future satellite data (e.g. ENVISAT) new questions concerning climate and weather will arise which can be studied with ICAPS more realistically than in terrestrial laboratories.SCIENCE How do aerosol particles affect climate and weather ? Aerosol particles (e.g. black carbon, sulfate) have a radiative effect on climate and weather by changing cloud cover and lifetime, amount of cloud water, cloud droplet concentration, and cloud precipitation efficiency; however these effects are still poorly understood. ICAPS can provide chamber experiments, but with atmosphere-like timescales. How is the atmosphere cleansed from particulate pollutants by clouds and precipitation ? Clouds and precipitation remove pollutants from the atmosphere very efficiently, but the various interaction forces between pollutants and droplets are not fully understood. Why does ice crystallize in so many varieties and how are ice crystals grown (nucleation) ? The formation and shape of ice crystals extremely sensitively depends on temperature and supersaturation, and requires so-called “ice nuclei” with very specific, yet unknown properties. Terrestrial measurements cannot realistically simulate “floating” nucleation. How do planets form and can we observe this process ? Planets grow in dust disks around young stars but the full theoretical process has never been experimentally investigated under solar nebula conditions, i.e. with realistic particle sizes and materials, and in a rarefied gas in microgravity. How do dust particles agglomerate ? Agglomeration of micron sized dust particles by sticking collisions is believed to be responsible for the early stage of planet formation. ICAPS will investigate these processes under a variety of conditions. What can we learn about comets without landing on them ? By observing the solar light scattered by dust particles in cometary tails and comae, and comparing these observations with measurements done on collections of well-known icy particles with ICAPS, we can refine our knowledge of the physical properties of cometary dust. ICAPS is a scientific programme to study under microgravity the interactions of cosmic and atmospheric particle systems ICAPS particles are solid or liquid, isolated or aggregated particle-particle interaction particle-light interaction particle-gas interaction