## 3 Results
### Advances in Other Mars ISRU Technology (2014-2023)  
Dust is a perennial problem on Mars, especially when a process must intake large volumes of Martian atmosphere. NASA funded some early work on dust mitigation [32]. MOXIE later performed far more extensive testing and modeling of dust mitigation in 2019-2022 [33; 34; 35; 36]. These results indicated that a suitable filter and inlet system can adequately protect a Mars ISRU system. The method of compressing the Mars atmosphere via freezing the CO\({}_{2}\) and then warming in a closed volume was further advanced [52] after being originally investigated by [23]. [PERSON] (2016) reported on electrolysis of water in a NASA report [53]. [PERSON] et al. (2017), [PERSON] et al. (2018) and [PERSON] et al. (2019) reported further results on the Sabatier process with NASA funding [54; 55; 56]. Oddly enough, none of these papers referenced [11], that had already demonstrated a Sabatier Mars ISRU system with high conversion twenty years earlier. The Sabatier process is well advanced. But it requires hydrogen, and hydrogen is scarce on Mars. [PERSON] and [PERSON] (2019) worked on a sorption compressor for Mars using rapid cycling, but progress was slow, and further work is needed [57]. There is a small amount of oxygen (about 0.13%) in the Mars atmosphere. Some concepts were developed to directly separate this oxygen from the other 98.87% of gases. We have already mentioned [24]. Recently, a new concept for selectively absorbing oxygen on Mars was proposed and is under study [58]. An alternative approach for Mars ISRU involving plasmas to dissociate CO\({}_{2}\) to O\({}_{2}\) is now under study, but O\({}_{2}\) separation and purification from product CO introduces a significant challenge [59]. In comparison, MOXIE always produces pure O\({}_{2}\) directly.  
[PERSON] and [PERSON] (2020) presented a review of Mars ISRU [60]. This publication provides a good overview of various technologies relevant to Mars ISRU. However, this paper was written before MOXIE carried out its major experiments and made important findings. For example, the review describes complex approaches to dust filtration, but MOXIE demonstrated that a simple HEPA filter is adequate [38; 39]. Under \"atmospheric capture\", the review provides an excellent discussion of the cryogenic approach. Under adsorption pumps, it did not report Reference [19]. It was perhaps overly optimistic about the possibility of accessible water at moderate latitudes and might benefit from Appendix C in Reference [1]. After this review was published, MOXIE demonstrated successful use of a scroll compressor and CO\({}_{2}\) electrolysis on Mars.  
[PERSON], [PERSON], and [PERSON] (2014) described a laboratory demonstration of an end-to-end Mars ISRU system at a significant scale (MARCO POLO project) [61]. This system:  
* Did not include dust filtering;
* Utilized the cryogenic method for CO\({}_{2}\) acquisition and compression developed by [PERSON] and co-workers in References [48; 52];
* Utilized the Sabatier process for CH\({}_{4}\) and O\({}_{2}\) production with water and CO\({}_{2}\) as feedstocks;
* Assumed that water-laden soil was available as a source of water.  
It was not clear how the \"Soil Hopper\" operates autonomously to deliver soil to the processor, what the \"soil\" actually is, how the water is distributed in the \"soil\", or whether the whole process is autonomous or managed.  
One oddity of the system is that the CO\({}_{2}\) collection system ran during the day and was dormant overnight, probably because it would run on solar power. But the freezing system is more efficient at night when it is colder, and the radiators can radiate to a much lower sink temperature. Any real system on Mars would collect CO\({}_{2}\) at night.