The JANUS camera onboard JUICE mission for Jupiter system optical imaging

Abstract

JANUS (Jovis, Amorum ac Natorum Undique Scrutator) is the visible camera selected for the ESA JUICE mission to the Jupiter system. Resources constraints, S/C characteristics, mission design, environment and the great variability of observing conditions for several targets put stringent constraints on instrument architecture. In addition to the usual requirements for a planetary mission, the problem of mass and power consumption is particularly stringent due to the long-lasting cruising and operations at large distance from the Sun.JANUS design shall cope with a wide range of targets, from Jupiter atmosphere, to solid satellite surfaces, exosphere, rings, and lightning, all to be observed in several color and narrow-band filters. All targets shall be tracked during the mission and in some specific cases the DTM will be derived from stereo imaging. Mission design allows a quite long time range for observations in Jupiter system, with orbits around Jupiter and multiple fly-bys of satellites for 2.5 years, followed by about 6 months in orbit around Ganymede, at surface distances variable from 10 4 to few hundreds km.Our concept was based on a single optical channel, which was fine-tuned to cover all scientific objectives based on low to high-resolution imaging. A catoptric telescope with excellent optical quality is coupled with a rectangular detector, avoiding any scanning mechanism.In this paper the present JANUS design and its foreseen scientific capabilities are discussed.

Thermal annealing response following irradiation of a CMOS imager for the JUICE JANUS instrument

“…The JANUS instrument consists of a main optical head unit, a proximity electronics unit and a main electronics unit that is located in the spacecraft radiation vault for camera control and power supply. The optical head unit includes the telescope optics and mounting structure, and a filter wheel to provide multispectral observations of the Jovian system using a greyscale detector [2].…”

Electro-optic and radiation damage performance of the CIS115, an imaging sensor for the JANUS optical camera onboard JUICE

“…The optical camera, called JANUS (Jovis, Amorum ac Natorum Undique Scrutator), is designed to provide both wide-field and high-resolution images to contribute to the study of the surfaces of the Jovian moons and the upper layers of Jupiter's atmosphere [2]. The telescope optical design has evolved into a Modified Ritchey-Chrétien format [3], with the 7 µm square pixels of the CIS115 [4] providing 15 µrads pixel -1 instantaneous field of view, which is expected to result in resolutions equivalent to 10 m pixel -1 on the surface of Ganymede whilst observing during close orbital mission phases.…”

Proton irradiation of the CIS115 for the JUICE mission

“…One instrument on JUICE is an optical camera called JANUS with a field of view (FOV) of 1.72x1.29 degrees and resolution up to 15 µrad pixel -1 [2]. When JUICE becomes the first spacecraft to orbit the moon of a gas giant, JANUS will undertake a detailed survey of Ganymede.…”

“…The JANUS camera uses a three-mirror anastigmat optical design [3] coupled with a Complementary Metal-OxideSemiconductor (CMOS) Active Pixel Sensor (APS), to achieve a FOV equivalent to 3.00 × 2.25 m 2 and a resolution equivalent to 1.5 mm pixel -1 from an observation distance of 100 m. At the closest approaches during its orbit of Ganymede (500 km), this resolution is equivalent to approximately 7.5 m pixel -1 , which is suitable for targeted observations of selected surface features. During higher orbits the ground sampling distance will be increased, and the trade-off of coverage with data volume and downlink rate capabilities is expected to require the use of pixel-binning for the majority of mapping that will inherently degrade the resolution.…”