Rosetta lander in situ characterization of a comet nucleus

Abstract

Rosetta is one of the cornerstone missions within the science program “Horizon 2000” of the European Space Agency (ESA). Its objective is the characterization of comet Wirtanen, which will be reached after 9 years of cruise in the year 2012. As comets are believed to be the most primitive bodies in our planetary system, having preserved material from the early stages of its formation, the Rosetta mission shall result in a better understanding of the formation of the solar system. The Rosetta Lander, part of the Rosetta payload, is contributed to the mission by an international consortium of research institutes. It will perform in situ measurements on the surface of the comet nucleus. The science objectives of the Rosetta Lander can be comprised by: • • determination of the composition of cometary near surface matter: bulk elemental abundances, isotopes, minerals, ices, carbonaceous compounds, organics volatiles -in dependance on time and insolation. • • measurement of physical parameters — mechanical strength, density, sound speed, electrical permittivity, heat conductivity and temperature. • • investigation of topology, surface structure including colour and albedo, near surface structure (strategraphy) and internal structure. • • the comets interaction with solar wind. The payload of the Rosetta Lander consists of nine instruments with a total mass of about 20kg. The Rosetta Lander system with an overall mass of about 85kg consists of a light weight structure of carbonfibre material, solar cells to provide power, a thermal control system securing operation without the use of radiactive heaters, a telecommunications system, using the orbiter as relay to Earth and a central computer, serving all subsystems and the payload. The lander will be ejected from the main spacecraft after selection of an adequate landing area from an orbit, about 1–5km above the surface of the nucleus. The actual descent strategy is highly depending on the (yet unknown) physical parameters of P/Wirtanen (like mass, shape and rotation period). Thus, a flexible landing concept, which allows the setting of the landing parameters interactively during the mission is required. Landing will take place on a tripod that includes a device that dissipates most of the impact energy and allows rotation of the main structure. At impact, a hold-down thruster and the shot of an anchoring harpoon will avoid rebound from the surface.