Raman Laser Spectrometer (RLS) is one of the Pasteur Payload instrument of the ExoMars 2020 mission, within the ESA’s Aurora Exploration Program. RLS is mainly composed by SPU (Spectrometer Unit), iOH (Internal Optical Head), and ICEU (Instrument Control and Excitation Unit), and will analyse Mars surface and sub-surface crushed samples by Raman spectroscopy. For the RLS Flight Model (FM) verification campaign, an end-to-end quick functional test was developed to evaluate the instrument performances stability. This test consists on a comparison of the centre pixel and the FWHM (Full Width at Half Maximum) of a set of Ne calibration lamp peaks, and was decided to be done before and after ever risky activity (transport, thermal tests, etc.) In the course of the end-to-end functional test carried out on RLS FM as part of the pre-delivery checks, an increment on the FWHM calibration lamp peaks was observed. Such performance variation was also noted to be dependent on the way the SPU thermal strap was assembled and the environmental conditions (P and T) in which the spectra were acquired. For that reason, a new SPU thermal strap assembly procedure was decided to be designed in order to ensure no extra negativeeffect was going to appear during the RLS FM installation on the ALD (Analytical Laboratory Drawer) and the instrument flight operation. In this paper, a deep exploration of the conditions in which such “de-focus” (probably due to an excessive thermal gradient between SPU structure and CCD) appears is carried out, demonstrating that the new thermal strap assembly procedure minimizes an incidental extra de-focus appearance during RLS installation on the ALD.
The Raman Laser Spectrometer (RLS) is one of the Pasteur Payload instruments within the ESA’s ExoMars mission. The RLS instrument scientific goal consists of perform in-situ Raman spectroscopy over different organic and mineral powder samples of the Mars subsoil. It consists of three main units: SPU (Spectrometer Unit), iOH (Internal Optical Head), ICEU (Instrument Control and Excitation Unit) which are interconnected by an optical and electrical harnesses (OH and EH).
The SPU is one of the most critical units of the RLS instrument. The Engineering Qualification Model (EQM) unit has been already delivered after a proper qualified campaign in a very demanding environment with very restrictive design constraints, including Planetary Protection requirements. Also, a complete set of functional tests had been carried out under representative environment, simulating not only Mars rover´s laboratory conditions (thermal range and pressure), but also the cruise phase. Previously, an exhaustive qualification campaign was developed with two different purposes: to mitigate the risks associated to new optical elements included in the design and without space heritage; and to obtain a detailed comprehension of their behaviour under Mars conditions for facing the Flight Model (FM) optical design with guarantee of success.
EQM results were successful in terms of Engineering, and a SWaP-optimized system had been reached. The acquired knowledge of that model has been used to implement little improvements into SPU FM for acceptance. For operations, a big amelioration has been the reduction of the image ROI on the Charge-Coupled Device (CCD) after the improving of the alignment of the inclination degree of the image plane on CCD under the tightly integration constrains, letting to download the minimum necessary data bytes. These improvements achieved by a proper analysis of the image on the SPU CCD will allow to evaluate far better the Raman spectrum effects.
SPU FM Mechanical, Thermal-Vacuum campaign has been already finished in order to accept for flight the current unit which will be already completed and “flight qualified” at RLS system level before the congress. If everything continues on this way, the desired Technology Readiness level, TRL 8 maturity level, will be reported during the following text.
In the framework of the ESA’s Aurora Exploration Programme and, in particular, of the ExoMars mission, the Raman Laser Spectrometer (RLS) will be in charge of performing out planetary Raman spectroscopy for the first time. The instrument is located inside the Rover at the Analytical Drawer (ALD) and will analyze powdered samples obtained from the Martian subsurface in order to determine the geochemistry content and elemental composition of the minerals under study. After the RLS instrument successful qualification, the Flight Model (FM) development and the acceptance verification activities started. Among the different units RLS is composed on, i.e. its three main units that are interconnected by optical fibers and electrical harness, iOH (Internal Optical Head), SPU (Spectrometer Unit) and ICEU (Instrument control and Excitation Unit) which also contains the Raman excitation laser diode, iOH FM information can be found in this paper. RLS iOH unit is in charge of focusing the Raman excitation signal onto the sample, receiving the Raman signal emitted by the sample and focusing this signal in the output optical fiber that is directly connected to SPU unit. As for the rest of RLS instrument FM subunits, and before their final assembly and system level tests, RLS iOH FM exhaustive and complete characterization process was carried out, not only at room conditions but also at relevant environmental conditions: vacuum condition along the operational temperature range with acceptance margins (from -50 to 8ºC). In this paper, and after to carry out the RLS iOH FM proper integration and alignment process, the activities accomplished during the performance verification and the obtained results are reported on