INTERSTELLAR ATOM AND PICK-UP ION FLUXES ALONG THE ULYSSES FLIGHTPATH

Neutral atom and pick-up ion flux computations using a hot model for h ydrogen, helium, oxygen and neon along the trajectory of the Ulysses s pacecraft, including predictions for the Extended Mission are reported and discussed. The feasibility of using absolute pick-up ion fluxes a nd pick-up ion flux ratios to derive the orientation of the heliospher ic upwind-downwind axis is investigated. Finally, the ratio of pick-up ion and neutral fluxes for helium and oxygen expected to be seen by t he Ulysses spacecraft are presented and their relevance for a determin ation of the long- and short-term averages of the total ionization fre quencies of neutrals is discussed.