ASEN 6116-001B, University of Colorado, Boulder
Review on methods to extract oxygen from lunar regolith Sid Bhilare
University of Colorado Boulder, USA
Abstract
In-situ resource utilization (ISRU) technologies have the potential to reduce long durational space exploration costs significantly. They also contribute significantly to human space exploration missions by making the mission cheaper and more independent by limiting if not eradicating the need for consumables’ replenishments. The heaviest consumable required by human beings is oxygen. Humans are prone to being vulnerable without a continuous supply of oxygen. Also, oxygen has applications as a propulsion fuel. Hence, in-situ production of oxygen is imperative for long durational human space exploration missions to become a reality. This paper reviews the available methods to produce oxygen from lunar regolith. It also attempts to gauge the merits and demerits of these processes from currently available data.
Furthermore, beneficiation, energy concepts and processing concepts are also briefly discussed.
Keywords: ISRU; ECLSS; ilmenite reduction; lunar regolith; oxygen production.
1. Introduction
With the upcoming Artemis program, NASA plans to place sustainable infrastructure on the lunar surface to demonstrate scientific exploration capabilities for deep space missions, including Mars.i Harnessing the lunar resources becomes imperative for this demonstration to be successful.ii,iii,iv,v NASA’s Lunar Surface Innovation Initiative is geared towards the development and demonstration of in-situ resource utilization (ISRU) on the Moon and increasing the test readiness level (TRL) of the developed technologies.vi,vii
One of the primary principles of any environmental control and life support systems (ECLSS) technology is to keep the crew alive. Humans need oxygen to stay alive and healthy as permanent brain damage can occur within 4 minutes of loss of oxygen.viii Oxygen is also the largest consumable by weight needed either for life support or propellant production.ix Hence, production of oxygen is arguably the most important goal for ISRU in terms of ECLSS and propulsion.ii,x Moreover, the need for metal mining on the moon can be justified by the need for lunar infrastructure for a sustainable lunar mission. Metals such as iron and titanium can be used for structural purposes and silicates can be used to make photovoltaic cells for solar panels.x It would hence be optimal if a chemical process concomitantly produced both, oxygen and metal components.
3.4. General comments:
While all the above-mentioned processes are demonstrated in the laboratory, their functioning in lunar environment poses serious limitations that need to be addressed.x For chemical reduction with hydrogen and methane, vapour phase pyrolysis and sulphuric acid reduction, high iron oxide content in the feedstock is required for obtaining high yields of oxygen.x,xviii Electrolysis of molten regolith does not require iron oxide rich feedstock particularly but the operating temperatures are very high. Whilst ilmenite is necessary for hydrogen reduction, optimising feedstock beneficiation has yet to be determined for improving the grade of the input ore.xv Also, optimising beneficiation methods for only one mineral might be short-sighted in the sustainable lunar exploration mission: Artemis. Most reduction methods have yet to be optimized for particle size to determine the size separation parameters of mineral ore. For meaningful conclusions to be drawn while comparing different methods for lunar regolith reduction, there is no existing standard ISRU language. Due to the lack of standard methods for data reporting and evaluation, communication about equipment
requirements has not yet been set up. Terrestrially, on earth, these standards are based on mass balancing. The oxygen gas extracted is expected to contain impurities; hence gas purification should be considered in the preliminary design phases to set up a value chain and increase its test readiness xix level (TRL). To fully recognize the implications of different extraction techniques, oxygen purification should be technologically demonstrated. Existing technologies being considered for gas xx xxi xxii xxiii purification are filters , centrifugal collectors , electrostatic precipitation , cryogenic purifiers , adsorptionxxiv xxiv xxv , absorption , adsorption in ion-exchange resins for water purification and membranexxvi processes.xix However, to select and develop a specific gas purification, more thorough understanding of the gas that emerges from the oxygen extraction process it’s needed. Based on current research, cryogenic processes seem promising with reversible adsorption with tailored adsorbents for purification and trace removal.xix With respect to design optimization, however, two or more of these technologies can be employed. An ideal system should also be redundant and easy to maintain along with being reliable and safe.
Sid Bhilare/University of Colorado Boulder, USA