## 3 Results
### Advances in Mars ISRU Technology 1996-2014  
In the period from 1996 to 1998, [PERSON] managed a small fund at JPL called the \"Mars Technology Program\". This fund provided seed money for low TRL tasks:  
1. A small grant to test a cell for SOEC of CO\({}_{2}\)[17]. This device utilized Pt electrodes and produced oxygen at TRL 2. Funds were not available to continue the work. 2. An experimental study of a Sabatier reactor that achieved very high conversion [18]. This work was complete at TRL 4. Oddly, two NASA studies about 18 years later did not refer to this work. 3. Joint JPL-Lockheed-Martin Astronautics (LMA) development of a sorption compressor [19]. A large sorption compressor was built and tested but the results did demonstrate that this approach had great merit in terms of power efficiency. 4. Several JPL chemical engineers demonstrated methane reforming with excellent conversion at TRL 3 [20]. The Sabatier process produces excess methane. In the period from 1996 to 2000, NASA JSC funded two important ISRU technology tasks, through the leadership of [PERSON]. These included:  
1. Demonstration of the reverse water gas shift process (RWGS) for Mars at TRL 3. [21; 22]. The work on the RWGS introduced an appealing possibility for Mars ISRU but funding was not available to continue the work (recent work on RWGS is discussed later in this paper). 2. CO\({}_{2}\) compression by freezing at TRL 3 [23]. Compression by freezing remains a possibility for the future. These tasks in the late 1990s represented important initial work at low TRL on Mars ISRU. NASA provided the funding, but the decision to fund these tasks rested locally with [PERSON] and [PERSON] at their respective centers. [PERSON] led a preliminary study of directly retrieving water from the atmosphere by adsorption in the 1990s at the University of Washington, but they appear to have relied on internal funding at the university [24]. This process appears to be very challenging. In the mid-2000s, engineers at the Pacific Northwest National Laboratory (PNNL) under the Department of Energy (DOE) support developed micro reactor technology [25] and ISC provided NASA support via [PERSON] for adapting this technology relevant to ISPP [26; 27]. As of about 2013, advances in several aspects of Mars ISRU were made at TRL\(\sim\)3 by intrepid researchers but Mars ISRU remained in an early evolutionary state. Advances in Terrestrial Energy Technology by DOE and the International Community Relevant to Mars ISRU  
It is a truism that NASA conducts space missions and DOE advances technology. Some of the energy technology supported by DOE over the years has important implications for Mars ISRU as well. Solid oxide technology for electrolysis and fuel cells has been under development worldwide for some fifty years for terrestrial applications [28]. Indeed, it was the terrestrial work prior to 2014 that enabled the MOXIE SOEC technology. NASA has already leveraged the terrestrial development work via MOXIE. Since then, the prospects for terrestrial SOEC technology have expanded greatly. A recent review [21] was downloaded 15,000 times from the journal _Science_. A Scopus search with SOEC in the title returns about 1000 papers; forty-five were published in 2014 and 127 in 2023. In some cases, this technology directly overlaps with applications to Mars ISRU. For example, the Danish-funded work on SOEC of CO\({}_{2}\) is relevant [29]. Over the past thirty years, SOEC technology was widely supported across the world, and by DOE in the US. We will not attempt to cover the very wide range of research advances in this field but there are many, and this area of research deserves its own separate review. The foundation laid down at OxEon Energy LLC (nee Ceramatec) by DOE funding over the years prior to 2013 provided the technology background that enabled the implementation of SOEC of CO\({}_{2}\) on Mars in the MOXIE Project beginning in2014. DOE-funded work on SOEC that developed the capability to build the MOXIE stacks for Mars is reported in [30; 31; 32].