A few months ago, a group at MIT did an analysis of the MarsOne mission that was fairly critical of the concept, on technical grounds. This week’s FISO telecon featured an update on the analysis they performed, particularly on the issue of the excess oxygen problem, and I wanted to make a few comments on what I read that were a little too long for twitter.
First, before I get to some alternative solutions to the excess oxygen problem, I did have one thing I noticed that surprised me–the caloric requirements. On page 19, they talk about a 3040 calorie per day diet per person. That seemed a bit on the high end. The only people I know that consume that many calories without getting fat are people with really active lifestyles (mountain climbers, marathon runners, etc). I wonder if those numbers came from ISS experience, where the effects of microgravity force them into a very strenuous exercise routine in the hopes of not having too bad of bone/muscle loss. This is one of those areas where knowing how much hypogravity we need would be really important. If you didn’t need anywhere near ISS-like exercise requirements to maintain health in a Mars-gravity environment, that would likely cut down significantly on the required calories, and might shift the ratio of carbs/proteins/fats from what was assumed on this page.
Now, moving on to the “excess oxygen problem”. Basically, using plant-based life support, and using the biomass numbers MarsOne estimated would be required to supply the required amounts of carbs/proteins/fats, they found that the plants produce too much oxygen. This leads to venting atmosphere overboard, and trying to make up with other constituents, leading to hypoxia. Their suggested solution was to isolate the plants, and come up with some sort of oxygen scrubber for storing the oxygen elsewhere for later use on EVAs and such.
But I think they may be overthinking this a bit. Here’s a few suggestions of alternative ways of solving the problem:
- Small animals (pets or food): The assumption in this analysis is that you only have humans and plants. Plants consume CO2 and produce O2, and humans produce CO2 and consume O2, and some fraction of the plants. What if you brought small animals along? Something that could eat parts of the plants inedible to humans. Could you increase the effective O2 consumption enough that way to counteract the rising O2 levels? If you picked something small that was edible (chickens? Cornish game hens? fish? etc.) it might allow you to replace some of the vegetable biomass dedicated to protein and fat production. I don’t know if this would completely solve the problem, but whether you eat the animals, or keep them as pets, it seems like you might have at least part of a solution there.
- Just Burn It: When you have an excess of O2 and a deficit of CO2 it seems like a combustion process might be in order. It would be relatively easy to take some Martian air, split it into CO and O, vent or store the O, and then run the process in reverse to combine CO with excess oxygen inside the habitat. This could be done to provide extra power at night using a solid oxide fuel cell. If this produces too much CO2, that’s easier to scrub using existing technology than O2 is. If you don’t feel safe handling CO in the habitat, turn it into CH4 using a Sabatier reactor, and burn that and recover the excess water from the combustion to put back into the Sabatier reactor.
- Mixed Food Sources: It might also be possible to pick some mix of food sources (some of it dehydrated pre-packaged food from earth, some locally grown) so that you optimize what you’re growing locally. For instance, if it turns out that your carbs are taking up the most area and generating the most surplus O2, maybe you can have more of those come in dehydrated ingredients from Earth for a while.
Ultimately, I don’t want to look like I’m ripping on the MIT team. They’ve done a very thorough analysis, and it’s almost always easier to point at potential flaws in an existing analysis than to create one from scratch. I just wanted to suggest some potential solutions. I particularly like #1. The whole idea of space colonist having to go 100% vegetarian always struck me as somewhat nutty. There definitely should be additional research to see if you can strike a balance with primarily biologically-closed life support in this way, but it seems like an obvious angle for further research/development
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