Michael Hecht responds to ECS Lecture questions
Michael H. Hecht delivered the ECS Lecture, Electrolysis on Mars: MOXIE and the Perseverance Mission, at the Plenary Session of the 240th ECS Meeting on October 11, 2021. Answers to questions posed during his lecture follow.
Photo courtesy of NASA/JPL-Caltech
Michael Hecht is the Associate Director for Research Management at the Massachusetts Institute of Technology (MIT) Haystack Observatory. Since 2013, he has been Principal Investigator for the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) instrument on NASA’s Mars 2020 Rover (Perseverance) mission, a technology demonstrator to validate the instrumentation and methodology to produce large quantities of oxygen from the Martian carbon dioxide atmosphere using solid oxide electrolysis (SOXE). From September 2019 to August 2020, Professor Hecht served as Deputy Project Director for the Event Horizon Telescope, the consortium that in 2019 delivered the first image of a black hole. His diverse experiences span planetary missions, observational astrophysics, space instrument and SmallSat development, planetary science, and project, program, and line management. Prior to joining MIT, he worked for 30 years at the NASA Jet Propulsion Laboratory (JPL), developing instrumentation for planetary missions. There he achieved the designation of Senior Research Scientist. At JPL, he served as Principal Investigator and Instrument Manager for the MECA (Microscopy, Electrochemistry, and Conductivity Analyzer) instrument on the Phoenix Mars mission. MECA operated through the summer of 2009, with major findings in microscopy, the physical chemistry of water in soil, and notably, in aqueous soil chemistry using electrochemical methods.
Prof. Hecht received his PhD in Applied Physics at Stanford University in 1982 after completing his BA in Physics at Princeton University and MS at MIT. His research has garnered numerous awards including the 2020 Breakthrough Prize in Fundamental Physics and 1990 Lew Allen Award for Excellence. His h-index is 51 with over 11,500 citations.
Q&A
Since there is some water on Mars, why not just electrolyze water to get oxygen and hydrogen that can then be used for rocket fuel or reacted with CO2 to form methane?
There is indeed lots of water on Mars, all in the form of ice or hydrated soil. Like any other mineral, you need to find it, excavate or extract it, and purify it before you can use it. We’ll do that someday, but for now MOXIE solves the big problem of oxygen (we’ll need 25 tons vs. 7 tons of hydrogen-containing methane) without having to do any of that! Even when we have water, we’ll probably still want to do CO2 electrolysis to make the best use of the resources.
In a full-scale oxygen production system for a crewed mission, will all CO need to be recirculated to the inlet to prevent reoxidation of the cathode, or is there any plan to use the product CO for other processes?
Only a tiny amount needs to be recirculated; you need at least 0.55% CO in the inlet to avoid oxidation. Plenty left for other purposes, such as fuel.
Is carbon deposition still a challenge for the current MOXIE on Mars?
Yes, we need to be very careful when we operate! But there is a lot of development going on down here on Earth to reduce that risk.
For full-size MOXIE, how will you provide the power? 25-30 kW is a fair bit. That’s lots of RTGs or quite a number of solar panels that need to be deployed. If solar, how to keep them clean?
First of all, this is the same 25-30 kW that will be needed by the crew when they arrive, so MOXIE just takes advantage of that. You would never do it with RTGs. NASA’s plan is a small fission reactor, a technology they call “kilopower.” It could possibly be done with solar (or beaming solar from space), but actually that’s more complicated because the sun isn’t always out!
Question about CO2 supply: As you establish an enclosed environment for human survival, what will be the advantages of recycling breathing exhaust, and has that architecture been thought out for the electrochemical plant?
Absolutely! Even in the ISS, breathing exhaust is recycled. The usual method is to scrub out the CO2 and recover as much oxygen from it as you can. MOXIE might be part of that solution but, unlike with the ISS, we don’t really have to save the CO2 we scrub out of the habitat air because there is plenty more of it outside to make oxygen from.
What challenges do you see for scaling up this technology? Will you change the chemistries to produce more oxygen? Finally, do you see this technology being applied to carbon dioxide sequestration in our own atmosphere?
MOXIE isn’t really appropriate for terrestrial climate change mitigation—it takes too much energy. Scaling up is an engineering problem, in process.
800 oC and 623 w/hr to generate 5-10 gm of Oxygen per hour seems energy intensive. What are your thoughts of scale-up of such a system with minimum energy consumption? Are there any alternatives of YSZ solid electrolytes or a completely different type of solid electrolyte that can operate at lower temperatures?
Most of that 623 W-hr (not W/hr!) is used to heat the system up, not to make oxygen, and that’s some you only do once with a production system. Keeping something at 800˚C doesn’t actually take any energy at all, you only have to make up the heat that leaks out—that’s why all the insulation is there. The main thing we have to do to reduce energy consumption is to improve the compression efficiency, and most of that will simply come from lowering the operating pressure (we could do that today if we had control over it).
It appears that it would be prudent, when in actual use for human consumption, to have multiple redundant units. If one fails, nine remain. Also, what overcapacity (2x, 3x, 10x) do you plan for?
That’s right. It’s not so much overcapacity but having spare units available, say eight units if we need six. The exact number depends on reliability.
Why did you mix unused CO2 with CO?
We’re not mixing them, it’s just that not all the CO2 is converted so some remains with the CO. The reason we can’t convert a larger fraction is because it would be impossible to do that without making carbon, and that would destroy the system.
Will enough oxygen to be able to launch already be generated before people arrive so if they needed to leave abruptly/early they could? Or is the logistics of leaving earlier due to the orbits not feasible so no need to worry about a year’s worth of oxygen before people arrive?
We’ll do better than that—we’ll have all the oxygen made before the crew even leaves Earth! But sadly, there aren’t really any options to leave Mars early, despite what you see in the movies.
Is any regeneration process planned (say burn a bit of your O2) to remove any carbon deposition or other fouling species?
Research so far has focused on avoiding it!
What is the energy comparison? The electricity into the SOEC and the power to heat the SOEC and surroundings is probably substantial. How does this compare to the energy required to deliver oxygen propellant to Mars itself?
Not even close! To begin with, there’s a “gear ratio” to consider. Getting 25 tons of O2 to Mars means getting at least 300 tons to Earth orbit, not to mention all the logistics of combining multiple launches to deliver it. But also remember, we need the same power system for the astronaut crew, whether or not we have MOXIE running before they get there.
How has repeatability and stability been so far?
Excellent! Each unit we build seems to get better, and going to Mars didn’t seem to degrade anything compared to the lab. We’re very excited about the performance.
Is it feasible to produce oxygen on Mars by electroyzing iron oxide?
Many other reactions are possible. I prefer ours because it’s so easy to collect CO2 compared to excavating anything.
What can you say about the quality of hydrogen for HEMFC vs PEMFC?
Sorry, I’m afraid I don’t know much about that.
