JANUS Optical Head Line of Sight Temperature dependence Characterization and Validation by on ground test

Abstract

JANUS (Jupiter Amorum ac Natorum Undique Scrutator) is the multispectral camera that, on board of JUICE (JUpiter ICy moons Explorer) ESA mission, will provide high-resolution images of Jupiter atmosphere and major Galilean icy moons surface: Europa, Ganymede, Callisto. Inertial pointing, mosaicking, object tracking, stereo imaging for DTM (Digital Terrain Model) and the peculiar Ganymede Libration measurements defined highly stringent requirement on the LoS (Line of Sight) knowledge of the JANUS OHU (Optical Head Unit). Once in flight, the JANUS LoS is expected to vary as consequence of thermal environment variations, in fact, orbit attitude change, spacecraft maneuvering and scientific payloads heat dissipations can modify the OHU temperature distribution. Optical elements translation and rotation have been predicted through a STOP (Structural Thermal Optical and Performance) Analysis, deriving a linear relation between LoS, value and uncertainty, and OHU structure temperature gradient. This relation has been validated thorough an on-ground and in-air characterization test, the results are presented in this paper. Test based coefficients allow real time and indirect LoS prediction & evaluation as function of OHU temperature sensor readings.