## 2 ARCHES LIBS Module
### Hardware Description  
The design specifications for the LIBS instrument mandated its compatibility with the standardized payload box system, featuring a cuboid envelope measuring \(340\,\mathrm{mm}\times 200\,\mathrm{mm}\times 237\,\mathrm{mm}\). This requirement ensured that the instrument could be stored in the payload fixture of both the lander and LRU2. Additionally, the instrument had to adhere to a mass limit of a maximum of \(2.5\,\mathrm{kg}\), facilitating manipulation by the LRU2 robotic arm. The frame of the payload box, constructed from lightweight carbon fiber sheet material, weighs approximately \(0.6\,\mathrm{kg}\), allowing for about \(1.7\,\mathrm{kg}\) of the payload mass to be allocated to the LIBSinstrument hardware. The payload box incorporates standardized mechanical and electrical interfaces for efficient data and power transfer between the rover and the instrument. In the case of the LIBS module, a slight modification to the cuboid payload box frame was made by trimming one edge. This adjustment allowed for the addition of a mechanical spacer while maintaining compatibility with the constraints for manipulation and transportation, as illustrated in Figure 1. The mechanical spacer serves to ensure that the LIBS instrument's optics are focused onto the target when the instrument is in contact with the sample's surface, eliminating the need for an optical focusing system. The initial design of the spacer involved a 3D-printed straight and slightly flexible bar with a length of 7 cm. This design facilitated a gentle placement of the module on the rock by absorbing some of the forces when contact was made. In a second design iteration, the original spacer was replaced by a cylindrical baffle of the same length as depicted in Figure 2. The baffle features a wavy cut at its outfacing end, enhancing stability during the positioning and placement of the module on the target. This modification serves to reduce loads on the rover's arm. Additionally, the baffle serves the purpose of enclosing the laser beam, contributing to the laser safety measures implemented in the design. For material ablation and the generation of the micro-plasma, the compact diode-pumped solid-state (DPSS) MicroJewel laser from Quantum Composers is employed. This passively Q-switched Nd:YAG multi-mode laser delivers pulses of approximately 8 mJ at a wavelength of 1064 nm with pulse durations of about 5 ns. While its nominal maximum power consumption is 20 W, during laser shots, we observed an actual peak current of 1.5 A and a peak power consumption of 72 W. The laser comprises two electrically connected sub-units: the laser driver, a small box measuring \(76\times 75\times 50\) mm\({}^{3}\), and the laser head embedded in a cylindrical aluminum housing with dimensions of 16 mm in diameter and 91 mm in length. To save mass and space, the laser head is mounted without a dedicated passive cooling system, which is typically required for continuous operation. Laboratory tests demonstrated that the laser system could operate without additional cooling when measurements comprised laser bursts with approximately twenty shots along a raster of about ten points. Figure 1: CAD model of LIBS payload module. The power distribution unit that comes with the standardized payload box is located in the lower separated partition in the rear in this perspective. Figure 3 displays the ARCHES LIBS measurement head encompassing all optical components of the LIBS system. The laser beam is emitted from the laser head, deflected by a beam splitter, and focused with an achromatic lens. After a final reflection from a wobble mirror, the laser exits the measurement head through a glass window and strikes the target at approximately a 7 cm working distance. All optical components are off-the-shelf parts from ThorLabs with a 1/2 inch aperture and anti-reflection coatings.