In-Situ Resource Utilization: Oxygen Production (ISRU)

The leading option for extracting oxygen from the Mars atmospheric carbon dioxide is to use a solid oxide electrolyzer, which removes one oxygen atom from the CO₂ molecule, ionizes it, and pulls it through a solid electrolyte by applying an electrical potential across the cell.  An assessment of the state-of-the-art is being performed to examine past and current development efforts in dry CO₂ solid oxide electrolysis (SOE), and to identify key enablers and critical technology gaps for achieving the scale-up, stable performance, and long life needed for future human missions to the Mars surface.  Differences in fabrication methods, reliability, scalability, thermal cycling, thermal ramp rates, thermal gradients among the ceramic layers, operating pressure, stack sealing, and longevity are also being evaluated.

Structural and thermal modeling of a small stack is leading to new designs for the manifolds to increase structural strength and improve gas distribution through the stack.  New manifold designs, 3D printed out of zirconia oxide to match the thermal expansion coefficient in the stack, will be tested for fluid and structural performance.  In FY19 and FY20, small scale SOE stacks from multiple commercial providers will be procured and independently tested and characterized in NASA facilities.

Oxygen production is part of the AES In-Situ Resource Utilization (ISRU) Technology Project which is developing the component, subsystem, and system technology to enable production of mission consumables from regolith and atmospheric resources at a variety of destinations for future human exploration missions. 

The overall goals of the ISRU Technology project are to achieve system-level TRL 6 to support future flight demonstration missions and provide exploration architecture teams with validated, high-fidelity answers for mass, power, and volume of ISRU systems.

The project's initial focus is on critical technology gap closure and component development in a relevant environment (TRL 5) for Resource Acquisition (excavation, drilling, atmosphere collection, and preparation/beneficiation before processing) and Resource Processing & Consumable Production (extraction and processing of resources into products with immediate use as propellants, life support gases, fuel cell reactants, and feedstock for construction and manufacturing).  The interim project goal is to complete ISRU subsystem tests in a relevant environment to advance the subsystem to TRL 6.  The project end goals are to perform end-to-end ISRU system tests in a relevant environment (system TRL 6) and integrated ISRU-exploration elements demonstrations in a relevant environment.

ISRU is a disruptive capability that enables more affordable exploration than today's paradigm where all supplies are brought from Earth, and allows more sustainable architectures to be developed.  The availability of ISRU technologies can radically change the mission architecture and be the sizing design driver for other complex systems already in development. For example, the current Mars architecture assumes ISRU production of up to 30 metric tons of propellant on the Mars surface in order to reduce the ascent vehicle landed mass by 75 percent and reduce Earth launch needs by at least 300 metric tons. If a decision was made to use storable propellants for the Mars ascent vehicle instead of ISRU-producible oxygen and methane, many other drastic changes to the architecture could be required, such as lander and ascent vehicle size, number of landers needed, surface operations for ascent vehicle fueling, and Mars rendezvous orbit. Other surface systems might become more complex or heavier if they are not designed to take full advantage of ISRU technologies. Examples include a more complex closed-loop life support system if resupply with ISRU water cannot be assumed, or a heavy, built-in habitat radiation shield if a water- or regolith-based shield cannot be added after habitat delivery to the surface.

Other system designers may also make decisions that reduce the benefit of incorporating ISRU into the mission, resulting in a larger or more inefficient ISRU system. For example, a non-continuous power source such as solar power would increase the required production rate and peak power of an ISRU plant, thus increasing its size and complexity due to hundreds of start-stop cycles.  However, a continuous power source, such as nuclear or solar power with storage, would allow an ISRU plant to operate continuously, thus minimizing its size, complexity, and power draw. These are only a few examples of how the inclusion of ISRU has ripple effects across many other exploration elements.

ISRU is also a new capability that has never before been demonstrated in space or on another extraterrestrial body.  Every other exploration system or element, such as power, propulsion, habitats, landers, life support, rovers, etc., have some form of flight heritage, although almost all still need technology development to achieve the objectives of future missions. This is another critical reason why ISRU technology development, leading to a flight demonstration mission, needs to be started now, so that flight demonstration results can be obtained early enough to ensure that lessons learned can be incorporated into the final design.

This technology development activity was transferred to the STMD Game Changing Development Program in October 2018.