Mechanical, Structural, and Thermal Qualification of Solid Oxide Elextrolysis for Oxygen Production from Mars Atmosphere Carbon Dioxide
Authors: Hartvigsen Joseph , Elangovan S , Elwell Jessica , Larsen Dennis , Clark Laurie M. , Meaders Thomas 
Published: February 2020

The NASA Mars2020 mission will land a Curiosity class rover on Mars with a set of seven new science instruments. One of these instruments, MOXIE, the Mars Oxygen ISRU (In Situ Resource Utilization) Experiment, will demonstrate oxygen production by solid oxide electrolysis of Mars atmosphere CO2. The rover host platform for the MOXIE project imposes severe constraints on mass, volume, peak power and total cycle energy, but it also offers an early opportunity to demonstrate non-terrestrial ISRU. The Martian atmosphere is 96% CO2, making it a valuable resource for extraction of oxygen for life support. An even greater oxygen production requirement is for ascent vehicle propellant enabling a return to earth. The fundamental operating principles and materials of the Mars ISRU application are no different than for the more common terrestrial hydrogen and synfuel applications. However, the environments the device will be subjected to in reaching Mars, and while operating on the Martian surface, create the need for some unique and highly rigorous qualification testing. Ceramatec has developed and qualified the Solid OXide Electrolysis (SOXE) device for MOXIE.

The thermal and mechanical environment requirements imposed on MOXIE are extreme. MOXIE must demonstrate that it can reach Mars intact and function through a minimum of 10 operational cycles once the mission begins on the planet surface, in addition to any baseline, characterization, and qualification cycles performed to the flight unit prior to launch. The SOXE qualification effort included subjecting the stack and thermal insulation system to multi-axis shock and vibration to simulate the loads of launch, entry, descent and landing. Since the stack will operate with a nominal 1 bar internal pressure against a Mars ambient pressure that varies around 10 mbar, seals are critical, and testing was conducted to verify oxygen purity throughout the anticipated operational cycles. The stack is held in compression to counteract the internal pressure, as well as to secure it within the thermal insulation package, requiring the demonstration of the mechanical load capability of the stack.

Due to the energy limitations on the rover, MOXIE will require nearly a full Sol’s (Mars day) energy budget to conduct a 2-4 hour operating cycle. The overall target of the program is to demonstrate MOXIE’s capabilities over the various seasons and at different times of day. With the run time limitations and the demonstration objectives, MOXIE is required to undergo thermal cycling between operations to extreme cold.

Ceramatec stacks have successfully met operating targets for oxygen production and oxygen purity after undergoing mechanical compression, shock and vibration, cold cycling to as low as -65°C, and through over 20 thermal/operational cycles. The MOXIE stack development and qualification process history will be presented in regards to meeting these challenging program requirements.

Acknowledgment: This material is based upon work supported by NASA through JPL’s prime contract under JPL subcontract number 1515459.