# Towards Lunar In-Situ Resource Utilization Based Subtractive Manufacturing
## 1 Introduction
### In-Space Manufacturing Processes  
In-space manufacturing is the transformation of raw (Section 1.2) or recycled materials (Section 1.3) into components, products, or infrastructure (Section 1.4) performed in  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Main Material Distribution** & **[\%]** \\ \hline Plastic & 39 \\ Steel & 19 \\ Aluminum & 15 \\ Glass & 12 \\ Rubber & 6 \\ Ceramic & 4 \\ Textile & 3 \\ Copper etc. & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Main material distribution of the required hardware across the phases [39].  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Material Nature** & **Mass** & **Specific Improvements for Spacecraft** \\ \hline Al-alloys & 60\% & -Improvement of material characteristics; \\  & & -Harmonization, for example, reduction of number of alloys; \\ Ti-alloys & 10\% & -Minimize cost (material price); \\  & & -Reduce manufacturing effort; \\ Steel incl. Super-alloys & 2\% & -Minimize cost (material price); \\  & & -Reduce manufacturing effort; \\ CFRP & 25\% & -Minimize mass (density); \\  & & -Improve manufacturing effort and capabilities; \\ Others & 3\% & -Minimize mass; \\  & & -Improve reusability. \\ \hline \hline \end{tabular}
\end{table}
Table 4: Expected material composition of future spacecraft [32].  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Group** & **Hardware Survey Objective** & **[\%]** \\ \hline
1 & Permanent Infrastructure and maintenance & 21 \\
2 & Permanent machinery and maintenance & 16 \\
3 & Long-lasting items and commodities & 20 \\
4 & Temporary and made-on-demand items & 46 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Summary of the identified hardware [39].  
space [41]. According to a NASA study [42], additive manufacturing, subtractive manufacturing and formative manufacturing technologies (Figure 4) are of primary interest in terms of ISRU (Section 1.2).  
Either way, in-space manufacturing is currently a rather new field of research with largely low technology maturity. In fact, this is supported if looking at the latest technology demonstrations (Table 7), while the materials examined also support the category of greatest need (Table 6).  
Nevertheless, current research also addresses metallic 3D printing with powder [53] and wire [54]. However, the technological maturity of wire-based systems is currently  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**PA** & **Process** & **Material** & **PoD** & **Source** \\ \hline
3 DP & & ABS & & [44] \\
12/2014 & & ABS, PEI-PC & Orbit & [45] \\ AMF & Polymer & ABS, PEI-PC & Orbit & [45] \\
02/2016 & manufacturing/recycling & PEI/PC & & [46] \\ REFAB & & (Ultem 9085) & & [46] \\
11/2018 & & & \\ \hline IOM & & Epoxy–carbon fabric & Ground demo & [47] \\
05/2017 & & & \\ AIMIS & Composite and Polymer & Photo-reactive resin & Parabolic flight & [48] \\
11/2019 & Manufacturing unlimited size & & \\ IMPERIAL & & Engineering polymers & Ground demo & [49] \\
01/2019 & & & \\ \hline POP3D & & PLA & Flight demo & [50] \\
03/2016 & & & \\ MELT & Composite and Polymer & PEEK & Ground demo & [51] \\
03/2018 & Manufacturing limited size & Carbon fiber-reinforced thermoplastics & Flight demo & [52] \\
05/2020 & & & \\ \hline \hline \end{tabular}
\end{table}
Table 7: State-of-the-art in-orbit manufacturing.  
Figure 4: NASA ISRU capabilities breakdown structure (2005) [43], redrawn from NASA [42].  
ahead of powder bed solutions. In fact, the transfer of the wire-based \"METAL3D\" system to the ISS is scheduled for 2023 [55]. In the long term, application on other planets with ISRU (Figure 5) and discarded hardware is to be expected.  
In summary, 3D printing is explored dominantly. On the other hand, if looking at the entire AM process chain, mechanical postprocessing in terms of subtractive machining is frequently required to achieve fit-for-purpose hardware [56].