The MEDUSA and MicroMED Experiments for the ExoMars Space Programme to Perform In Situ Analysis of Martian Dust
Creators: name: Ventura, Sergio
Publisher: name: Università degli Studi di Napoli Federico II
Year: 2011

description: This thesis describes the work for the PhD in Aerospace, Naval and Total Quality Management of the University of Naples “Federico II” from 2008 to 2011. The work was mostly performed at National Institute of Astrophysics (INAF) - Astronomical Observatory of Capodimonte, Naples, Italy, and partly at European Space Agency (ESA) - European Space Research and Technology Centre (ESTEC), Noordwijk, The Netherlands. The activities for the present thesis were focused on the investigation of dust in the Mars atmosphere. The key subjects covered are: investigation of Mars with the ESA-NASA ExoMars Programme; study of the MEDUSA experiment for the analysis of dust in the Martian atmosphere at ground level; study of the MicroMED instrument, aimed at miniaturizing MEDUSA for the DREAMS proposal package (ExoMars EDM 2016) or other future mission opportunities.

The work starts with a detailed description of the Martian boundary conditions, based on past exploration missions, with emphasis on properties of grains dispersed in the atmosphere.

The original work performed for this thesis is within the ESA-NASA ExoMars Programme, a challenging space project for the exploration of Mars. Tasks have been accomplished on several aspects of the MEDUSA and MicroMED experiments, as possible scientific payload of the mission modules foreseen for landing, and on some specific aspects of the ExoMars Programme, during the permanence for a period of 3 months at ESA-ESTEC.
The ExoMars Programme, in its present configuration, includes a mission in 2016 (EDM, i.e., Entry Descent and Landing Demonstrator Module, and TGO, i.e., Trace Gas Orbiter) and a mission in 2018 (Rover). Some tasks were accomplished at ESA-ESTEC: 1) The preparation of the Announcement of Opportunity (AO) for the selection of the ExoMars EDM 2016 payload by checking the engineering requirements, defined in the EDL Demonstrator Module Payload Experiment Proposal Information Package; 2) A review of the requirements of the scientific sensors of the Pasteur Payload (PPL) on board the ExoMars Rover allowing the update of the definition of the top level science, measurement, accommodation and deployment requirements; 3) The elaboration of the ExoMars Rover Reference Surface Mission to define the nominal operative scenario of the ExoMars Rover on the surface of Mars by determining the power and energy utilization timelines of the PPL, Drill and Sample Preparation and Distribution System (SPDS) on the basis of the Rover engineering requirements, energetic resources, and SPRD.

As a member of the MEDUSA and MicroMED instrument teams, I performed detailed studies on fluid dynamics and light scattering aspects, relevant for the instrument development. The goals have been to prepare and perform numerical and experimental analyses on the working principle of sensors for aerosol measurements (i.e., aerosol aspiration and light scattering analysis of the dispersed grains) and, then, to contribute to the design of the two instruments.
The MEDUSA instrument was designed by INAF-OAC and selected for the ExoMars Humboldt Payload (HPL) mission to accomplish measurements of dust grain sizes, size distribution and concentration in the grain diameter range of 0.2-20 μm, and the water vapour abundance at the Martian landing site. The work performed during this thesis has included numerical and experimental activities to characterize the functionality of the MEDUSA breadboard. A Computational Fluid Dynamics (CFD) analysis was performed to study the fluid flow and particle trajectories in the MEDUSA Optical Stage (OS, the optical module where light scattering analysis on crossing grains is performed). A pre-processor for discretizing the domains and a numerical solver were used. The CFD analysis was done by simulating aerosol flows and solving fluid dynamics fields by coupling the Navier-Stokes equations in finite volumes (Eulerian approach) with the dynamics equations for discrete particles phases (Lagrangian approach). Experimental tests were executed both in laboratory simulated Martian conditions on the MEDUSA OS breadboard and its optical components in order to evaluate the validity of the working principle and functionality.

In the end of 2009 ESA and NASA descoped the Humboldt Payload according to a general design review of the ExoMars Programme, deciding to re-select the payload, via an Announcement of Opportunity, for a new lander concept, the ExoMars EDM 2016, with a maximum scientific payload of 3 kg. Therefore, a relevant fraction of the work for this thesis was focused on changing from MEDUSA to a new miniaturized and efficient system, called MicroMED, to perform measurements of grain size in the Martian lower atmosphere. 
The baseline design of MicroMED was aimed at simplifying the sub-systems and the working principle of the instrument in order to reduce the resource requirements. The new goal for MicroMED included drastic reduction of the mass from about 3 kg to less than 0.3 kg, and power consumption from about 21 W to 1-1.5 W. Therefore, a simplified optical working principle with a single detection channel in a wider angle from normal-direction scattering was adopted, instead of four channels (forward and backward direction for scattering detection, each one amplified both with high and low gain) implemented in MEDUSA. An accurate fluid dynamics re-design of the instrument was done in this thesis in order to optimize the device functionality, allowing MicroMED to accomplish the same scientific requirements of MEDUSA for what concerns the measurements of the dust grain sizes.

Part of the thesis activity was also dedicated to the definition and technical organization of the DREAMS (Dust characterization, Risk assessment and Environmental Analyzer on the Martian Surface) package for the ExoMars EDM 2016 mission, which included in its proposed version the MicroMED instrument.