Two stage battery system for the ROSETTA lander

The ROSETTA mission, lead by ESA, will be launched from Kourou by Ariane V in January 2003 and after a long trip, the spacecraft will reach the comet Wirtanen 46P in 2011. The mission includes a lander, built by an European consortium under german leadership (DLR), on which France has a large participation and is concerned by providing a part of the payload and some lander sub-systems. Among these, CNES delivers a specific battery assembly in order to comply with the mission environment and profile, avoiding particularly the use of radioisotopic heaters and radioisotopic electrical generators commonlly used for such missions far from the Sun. The battery includes a pack of lithium-thionyle sulfate cells having a large capacity and a small self discharge rate, able to achieve the nominal lander mission on the comet. A secondary stage, including rechargeable lithium-ion batteries, is used as complement for the main phases of the nominal mission, but is mainly aimed to achieve the extended mission when the comet will come close enough from the Sun in conjunction with the lander solar cells. The battery includes also a specific electronic system dedicated to the battery handling and secondary cells balancing, a mechanical and thermal structure designed, built and qualified in order to comply with low mass constraints. This battery system is presently integrated into the Rosetta Lander flight model and will leave the Earth at the beginning of next year. For the future, such a development and experience could be usefull in the frame of other similar cometary missions. (C) 2003 International Astronautical Federation.