Rosetta Lander in situ characterization of a comet nucleus

Rosetta is one of the cornerstone missions within the science program,,Hori zon 2000" of the European Space Agency (ESA). Its objective is the characte rization of comet Wirtanen, which will be reached after 9 years of cruise i n 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 i ts 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 r esearch institutes. It will perform in situ measurements on the surface of the comet nucleus. The science objectives of the Rosetta Lander can be comp rised by: determination of the composition of cometary near surface matter: bulk elem ental abundances, isotopes, minerals, ices, carbonaceous compounds, organic s volatiles in dependance on time and insolation. measurement of physical parameters - mechanical strength, density, sound sp eed, electrical permittivity, heat conductivity and temperature. investigation of topology, surface structure including colour and albedo, n ear 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 abou t 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 radioctive heaters, a telecommunications system, using the orbi ter as relay to Earth and a central computer, serving all subsystems and th e payload. The lander will be ejected from the main spacecraft after select ion of an adequate landing area from an orbit, about 1-5km above the surfac e of the nucleus. The actual descent strategy is highly depending on the (y et unknown) physical parameters of P/Wirtanen (like mass, shape and rotatio n period). Thus, a flexible landing concept, which allows the setting of th e 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 h old-down thruster and the shot of an anchoring harpoon will avoid rebound f rom the surface. (C) 1999 published by Elsevier Science Ltd. All rights res erved.