CCDs for the Rosetta Science Imaging System OSIRIS

Abstract

Three different types of CCD detectors have been especially designed under contract of MPAE for space applications. All designs were derived from commercially available devices. Modifications were successfully implemented in order to improve the detectors for the intended purpose and operational constraints. The most recent project was started at EEV (UK) to obtain highresolution imagers of 2Kx2K pixels for the Optical, Spectroscopic and Infrared Imaging System (OSIRIS) on-board the main spacecraft of the European Rosetta mission. The spacecraft will be launched early in 2003 and is scheduled to meet comet 46P/Wirtanen in 2011 at a solar distance of more than 4 AU. The spacecraft will escort the comet nucleus for several years at close range (rendezvous) down to ∼lkm on its way to perihelion at approximately 1 AU. During the mission, the CCD detectors are exposed to solar irradiation for more than 10 years. This constitutes a major risk for the performance of the devices because performance degradations such as deteriorated charge transfer efficiency and enhanced dark charge generation have to be taken into account. Protection against irradiation is consequently a design driver for the OSIRIS cameras. The CCD design is based on backside illuminated EEV CCD42-40 devices. In the course of improvements, lateral (shielded) anti-blooming overflow protection was introduced to these devices so that weak cometary features can be imaged near bright regions in long duration exposures. With the help of a complex temperature regulation technique, low temperature operations (≈160K) can be achieved as well as high temperature detector annealing at 400K for the in-flight bake out of radiation defects.