Type: Zeitschriftenaufsatz (non-reviewed)
In-Situ Resource Utilization (ISRU) technologies pave the way for a sustainable colony on the Moon. Above all, the construction of structures using only the available resources is an important factor in reducing costs and logistical effort. The MOONRISE project aims to melt lunar regolith using lasers on mobile platforms for the Additive Manufacturing of structures. This process is called Mobile Selective Laser Melting (M-SLM) and has the advantage that only electrical energy and a moving system are required. In order to validate the laser melting of lunar regolith simulants on ground, a vacuum chamber was designed to host powder material at pressures of around 10-2 mbar. Laser exposure and high speed monitoring were performed through a window. Prior to finalizing the payload design, the type of laser source, appropriate spot size, power, and duration of exposure were determined by means of experimentation. For reasons of cost-efficiency, the payload development approach is to profit as much as possible from components commercial off-the-shelf (COTS), i.e. commercially available components, which have no formal space qualification. These components, e.g. built for automotive application, often withstand harsh environments or even have space heritage without the costly and long-lasting process of formal space qualification. For MOONRISE, COTS parts – partly based on space heritage - have been screened in environmental tests and selected for the payload. A detailed preliminary design review of the MOONRISE payload was conducted in 2019. The payload mainly consists of a printed circuit board (PCB) for system communication, a fiber coupled diode laser, an electrical diode driver, a beam focusing optics, and an LED illumination. For baseline operation, a laser power of typically 70W will be applied for 6s to the lunar surface at a distance of about 25cm. The LED illumination is supporting visualization of the molten regolith by external cameras. The MOONRISE payload can be accommodated to a rover or a robotic arm to ensure mobility for the melting experiments. Following that, an Engineering Model (EM) has been assembled and tested for functionality. The dimension of the payload is 1.5U CubeSat and it has a mass of about 2.5kg with further reduction potential towards flight model (FM) development. In the following steps, environmental tests, such as vibration and thermal-vacuum cycling, will be carried out with the EM. As laser melting of regolith under vacuum conditions produced dense material, tests were continued under low gravity conditions in the large-scale research device Einstein-Elevator at the Hannover Institute of Technology (HITec) of the Leibniz University Hannover (Germany), which is a further development of a classical drop tower with which experiments are carried out under conditions of microgravity . It allows experiments under zero gravity conditions for about four seconds. The flight can be repeated up to 300 times per day. The Einstein-Elevator also enables adjustment of the gravity level from 0 to 5g, a feature that was used to carry out melting experiments with the EM under lunar gravitation conditions.