An autonomous control software embedded in a custom-designed electronic architecture for ExoMars' RLS instrument to analyze samples at Mars surface

ExoMars mission is ESA’s greatest commitment to reach the Red Planet in 2023 (ExoMars will take off in September 2022 and the lander will reach Mars in June 2023). ExoMars2022 aims to search for past/present life traces on Mars and to investigate the geochemical and environmental evolution of Mars. To fulfil these objectives, the Rosalind Franklin rover will be equipped with a large quantity of instruments that will allow to select and collect samples up to 2 meters in depth through a drill. Once samples are collected, the rover Sample Preparation and Distribution System will crush the samples and deliver the powdered material within the Analytical Laboratory Drawer (ALD). MicroOmega, MOMA and Raman Laser Spectrometer (RLS) are the three key scientific instruments included in ALD that will perform combined analysis to extract the most information about composition of Mars subsurface

RLS is a Raman spectrometer which provides a powerful tool for identification and characterization of minerals and biomarkers. The instrument is made up from several units: a laser for samples excitation, an internal optical head (iOH) which collects the Raman signal returned by the sample and forward to through the Spectrometer Unit where it is diffracted and projected to a CCD. All the mentioned operations are controlled by ICEU, (Instrument-Control & Excitation-Unit) a sophisticated custom electronic box designed to support an autonomous software control based on an exclusive hardware architecture composed by a FPGA (where low level drivers are hosted), a LEON2 (where Application Software (ASW) is running) and associated peripherals will be used by SW to perform assigned tasks. Therefore, RLS ASW purpose is to command and control all RLS critical elements, such as the optical head focusing mechanism, the CCD imager, and thermal control for both CCD (in order to keep it cool) and laser source (to warm it until its working temperature).

In order to obtain the maximum scientific performance at the Mars surface while optimizing the limited operation opportunities for RLS, according to the Rover Reference Surface Mission, and solving the technical difficulties intrinsic to space instrumentation, the RLS team has developed an advanced embedded software in a custom-hardware-architecture that provides an automated control of all RLS subsystems as well as post-processing capabilities to perform prompt in-situ analysis of Raman spectra.

In addition, it also includes the logic to perform automated Raman acquisitions and applying post-processing algorithm to adapt the sample acquisition parameter of every sample spot under analysis, reducing the sample fluorescence, removing undesired spikes due to Cosmic Ray impacts and by calculating the acquisition integration time. The objective of those algorithms is to maximize the Raman signal intensity of the acquired spectra, avoiding saturation level on the detector.

The RLS ASW, commands the autofocus system to guarantee that iOH is optimally focused in the accurate acquisition position over the sample. This is part of the AF algorithm function which allows effective Raman signal collection by maximizing the SNR. Finally, RLS manages communications with Rover’s MMS (Mission Management SW) implementing ‘CANopen Controller IP Core’ protocol.