Alignment procedure for detector integration and characterization of the CaSSIS instrument onboard the TGO mission

The Colour and Stereo Surface Imaging System (CaSSIS) is a high-resolution camera for the ESA ExoMars Trace Gas Orbiter mission launched in March 2016. CaSSIS is capable of acquiring color stereo images of features on the surface of Mars to better understand the processes related to trace gas emission. The optical configuration of CaSSIS is based on a three-mirror anastigmatic off-axis imager with a relay mirror; to attain telecentric features and to maintain compact the design, the relay mirror has power. The University of Bern had the task of detector integration and characterization of CaSSIS focal plane. An OGSE (Optical Ground Support Equipment) characterization facility was set up for this purpose. A pinhole, imaged through an off-axis paraboloidal mirror, is used to produce a collimated beam. In this work, the procedures to align the OGSE and to link together the positions of each optical element will be presented. A global Reference System (RS) has been defined using an optical cube placed on the optical bench (OB) and linked to gravity through its X component; this global RS is used to correlate the alignment of the optical components. The main steps to characterize the position of the object to that of the CaSSIS focal plane have been repeated to guide and to verify the operations performed during the alignment procedures. A calculation system has been designed to work on the optical setup and on the detector simultaneously, and to compute online the new position of the focus plane with respect to the detector. Final results will be shown and discussed. <P /

Hydrothermal Alteration of Ultramafic Rocks in Ladon Basin, Mars—Insights From CaSSIS, HiRISE, CRISM, and CTX

The evolution of the Ladon basin has been marked by intense geological activity and the discharge of huge volumes of water from the Martian highlands to the lowlands in the late Noachian and Hesperian. We explore the potential of the ExoMars Trace Gas Orbiter/Color and Stereo Surface Imaging System color image data set for geological interpretation and show that it is particularly effective for geologic mapping in combination with other data sets such as HiRISE, Context, and Compact Reconnaissance Imaging Spectrometer for Mars. The study area displays dark lobate flows of upper Hesperian to early Amazonian age, which were likely extruded from a regional extensional fault network. Spectral analysis suggests that these flows and the underlying rocks are ultramafic. Two distinct altered levels are observed below the lobate flows. The upper, yellow-orange level shows hundreds of structurally controlled narrow ridges reminiscent of ridges of listwanite, a suite of silicified, fracture-controlled silica-carbonate rocks derived from an ultramafic source and from serpentine. In addition to serpentinite, the detected mineral assemblages may include chlorite, carbonates, and talc. Kaolin minerals are detected in the lower, white level, which could have formed by groundwater alteration of plagioclase in the volcanic pile. Volcanism, tectonics, hydrothermal activity, and kaolinization are interpreted to be coeval, with hydrothermal activity and kaolinization controlled by the interactions between the aquifer and the hot, ultramafic lobate flows. Following our interpretations, East Ladon may host the first listwanite ridges described on Mars, involving a hydrothermal system rooted in a Hesperian aquifer and affecting ultramafic rocks from a magmatic source yet to be identified

Two-dimensional stokes flow around a heated cylinder: A Possible application for diapirs in the mantle

It is widely assumed that the separation of metal and silicates in a homogeneously accreted protoplanet occurred rather rapidly. The process of core formation through the descent of large, hot, iron-rich bodies through a cold, silicate protoplanet is discussed. If iron diapirs sink toward the planet center with the Stokes velocity, they would require more than 800 Ma to form a core in the case of a planet similar to the Earth. We therefore implement a temperature-dependent rheology for the silicate material surrounding the diapir, which leads to a reduction of the drag force exerted on the iron drop. We compare the drag force for different sinking velocities to the body force on the diapir and find that the terminal velocity in the temperature-dependent viscosity model is a factor of 30 higher than that in an isoviscous medium. On the basis of these results, the core formation time for the Earth could be as little as 30 Ma

Twenty months development for the Cassis telescope: re-use building blocks and concurrent engineering

On board of the ExoMars Trace Gas Orbiter (TGO), the Colour and Stereo Surface Imaging System (CaSSIS) developed under the lead of University of Bern, has the mission to provide stereo images of the planet's surface in colour at a resolution of better than 5 m (4.54m from a circular orbit of 400 km) for enhancing our knowledge of the surface of Mars [1]