An experiment to study the solar wind-comet Halley interaction and the cometary environment with 3D electron distribution and thermal positive ion measurements on board the GIOTTO spacecraft

The GIOTTO RPA-COPERNIC experiment measures the three-dimensional distribution of less than 10 eV to 30 keV electrons, and the composition and distribution of thermal positive ions including the clathrate hydrates in the mass range 10-203 amu. The electron measurements will mainly define the structure of the cometary plasma and its interaction with the solar wind. The electron electrostatic analyzer (RPA 1-EESA) contains a quadrisphere analyzer with 360 x 14 deg field of view associated with 17 detectors, giving the three-dimensional distribution every 2-sec (half-spin of the spaceprobe). The measurements of ions, of their clathrate hydrates, and of their mass distribution close to the comet will provide a sensitive probe of the interaction processes as well as information on the spatial distribution and composition of these solid, gas and plasma components of the cometary environment, and of the chemical composition of the cometary nucleus (parent molecules). The RPA 2-PICCA sensor contains a hemispherical analyzer associated with 2 detectors measuring thermal positive ions close to the comet with high sensitivity, low background, and good mass resolution.