Design and Testing of a Sample Handling System for Operation on the Lunar Surface

摘要

Here we provide an in-depth description of the design concepts and verification strategy for the sample handling system (SHS) used for preparing lunar regolith samples for analysis by laser ablation ionization mass spectrometry (LIMS). The SHS is an integral part of a reflectron-type time-of-flight LIMS (RTOF-LIMS) system that allows for direct and sensitive chemical composition analysis of individual regolith grains in-situ on the lunar surface. The RTOF-LIMS measurements can provide the full element and isotope composition of the sample material (mass range up to m/z ~1,000) for each individual laser pulse applied to the sample surface. The CLPS-LIMS instrument is manifested for a robotic mission (stationary lander) within NASA's Artemis Commercial Lunar Payload Service (CLPS) program to the lunar south-pole. The lander will provide upon request lunar regolith (grain sizes < 5 mm) to the LIMS instrument's collection funnel for further sample manipulation by the instrument. The sample material is sieved in a two-stage process assisted by vibrating the funnel and sieve assembly at their first global resonance frequency. The sieving process removes grains with particle sizes larger than 1 mm, as these would interfere with achieving the required sample surface quality for reliable LIMS measurements. Control of the sample roughness is important to ensure consistent laser ablation conditions during sample analysis and thus reproducible chemical composition determination of the sample material. The sieved sample material is deposited into a 1.5 mm deep and 5 mm wide channel at the edge of a rotating circular carousel disk with a diameter of 187 mm. The system creates, with the help of passive shaping brushes and a skimmer blade, a well-defined planar sample surface with height variations less than ±200 μm in > 90% of the conducted test runs. After chemical analysis by LIMS, cleaning brushes remove the remaining material from the channel and prepare it for new sample material delivered by the lander platform. The SHS system allows for indefinite sample material to be analyzed. Two reference samples are included along the edge of the carousel for calibration purposes of the chemical analysis performed by the LIMS instrument. The SHS was tested and validated at inclinations up to ±10° off the nominal plane of operation, as an angled landing position of the lunar lander is possible. The observed overall sample utilization efficiency was influenced by losses during sieving and the intentional overfilling of the carousel channel. Effects on the sample surface quality have been studied and found to be within the requirements for subsequent analysis of the regolith by LIMS. Tests were conducted using regolith simulant with grain sizes of up to 5 mm (LHS-2, Space Resource Technologies, USA, complemented with larger grains). To test sieving efficiencies in the lunar gravity environment, cork grains with low specific mass were used to simulate the reduced gravity. Finite element analysis of the SHS shows compatibility with vibration loads as defined by NASA's General Environment Verification Standard (GEVS).