YHABFT: MIT MarsOne Analysis — Alternative Solutions to the Excess O2 Problem

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:

  1. 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.
  2. 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.
  3. 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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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
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15 Responses to YHABFT: MIT MarsOne Analysis — Alternative Solutions to the Excess O2 Problem

  1. Jalmar Ytstebo says:

    Unless already included in the report’s calculations: (haven’t read it)

    Mycobacteria and other bacteria and fungi could process non-edible plant parts and human waste to nutrients, consuming oxygen in the process. Closing the biological cycle this way should hopefully reduce the problem significantly. (More robust than chemical/combustion alternatives; Would work better with soil than hydroponics BTW).

    Fish/Animals would probably add more complications than assistance to this, but might be worth it anyway for the psychological relief from having fellow creatures around and getting non-vegetarian food now and then for variety.

  2. ken anthony says:

    It’s nutty on several levels, but all are fixable. 1) It’s not a closed system and they should not think of it as such. 2) ISRU should apply to equipment as well as raw materials. 3) Volume is not limited to what they bring with them and should consist of separate areas that can each fail without jeopardy to all. 4) Private ownership works even for just two people, but more is better.

    1) Worst case, they vent an entire area and redo from constantly restocked storage. Limiting vegetation is nuts. Seeds are natural space travelers, send everything. Let the colonists individually experiment and trade (including herbs and spices, salt?.) Same for animals, start small, eventually any imaginable (they have no space limitation after transport.)

    2) They may need to rethink what a module is. Things break. This should NEVER require earth resupply. Some crew needs to understand the chemistry so they can fix things themselves. Others need tool making skills which allow them to make anything they need. Give the 3D printers to those w/o skills (who will trade their production for raw materials produced by others.)

    3) Is self explanatory. You never put all your eggs in one basket. Failures should all be graceful and recoverable.

    4) You don’t need to micromanage people’s lives. Economics works better than planning. Give people ownership and free trade, where each can specialize on their own areas of interest, makes people happier and results in better than anything that can be planned.

  3. ken anthony says:

    Put a spark plug in the ceiling and add hydrogen?

    Make habitats really big. Huge. Mind blowingly large. So if they discover a problem, they can panic knowing they only have a few hundred days to fix it.

  4. Mark Holum says:

    A better solution than animals might be mushrooms! Easily digestible, tasty, make less mess, and are fairly simple to grow…

    If I’m reading correctly, the basic issue is cellulose. Plants produce too few calories per unit of CO2 because they produce so much of an undigestible structural carbohydrate. Small animals therefore won’t solve the problem, unless they can digest cellulose. Birds and rodents therefore are not really a solution. Hare’s could be, but they are already a bit big. A better solution is something like aphids or termites, which can then be fed to something else. Or you could do this chemically, and use a bioreactor with something like the protist triconympha and just extract the glucose.

    The complexity of all these solutions makes open cycle with ISRU sound appealing, but I think the more general closed cycle approach is the one worth pursuing.

  5. ken anthony says:

    If you can ignore the die in X days headlines, the MIT report is exceptionally positive about the Mars One plan. The issues they highlight are all entirely corrected with minor changes. They assume higher launch requirements when the reality is Mars One plans on slightly too few initially, but way too many on follow up. They only need 2 but plan on 10 for every following 4 crew. Plus the MIT report is calling for $300m per FH, when the actual price for FH and lander should be under $200m (much less with higher flight rates.) Keeping the Mars One continuing cost of $3b would actually allow 30 colonist (rather than 4) per launch window only limited by the farming rate (which they should have a good handle on by then and know exactly what they need to scale up to whatever they require or more.)

    The really good news is if they come up with something that works as a closed system, it definitely works for the reality of an open system. This is why you want to send as many colonists as you can afford which makes industry easier (you want at least 2 vendors for every essential commodity) and even if Bas Lansdorp doesn’t believe in private property (other than the colonists being his private wage slaves) they are going to own their own property eventually so they might as well do that from the start (like all successful colonies.)

    It all comes back to funding and the lander. I bet Elon is playing his cards close to the vest regarding the lander because he still hopes for NASA development funding but is probably moving ahead behind the scenes anyway.

    After the first crew landing things should begin to move fast as many of the sea monsters will have been vanquished. It’s very exciting, but now we sit and wait.

  6. philip hahn says:

    Sounds to me like a feature…. a little bit of hydrogen will make an endless supply of water.

  7. Peterh says:

    If a farm is producing excess O2, it’s also producing surplus biomass, and will need replacement CO2. Compost, mix with native sand and clay, long term O2 surplus solved, and farm capacity to produce food is expanded for the next batch of colonists. Still needs expanded greenhouse space.

    Allowing that the tool kit going with the first colonists should include the means to bootstrap production from local materials, later colonists could get by with less mass shipped from Earth. Everything the colony needs to survive should eventually be producable locally.

  8. George Turner says:

    I’m not sure how either Mars One or the MIT group approaches extracting nitrogen from the Martian atmosphere, which MIT indicates would take up a lot of mass and volume. Distillation (easy with CO2), pressure-swing adsorption, or membrane separation are obvious candidates, but you can also strip CO2 from a gas stream by bubbling the gas through down flowing water. Once ISRU efforts are already able to build new habitats capable of holding pressure and can make pumps for both gases and liquids, then using water (which you have to be making anyway) might be the most easily expandable and maintainable long term option. (modeling link)

  9. ken anthony says:

    Their biggest problem might be how to store the abundance they will have. We know there are risks, but do we fully appreciate the opportunity?

    Sending doctors and researchers on the first landing is just stupid. The two essential colonists are a chemist and a machinist/mechanic. The first landing isn’t about science, it’s about survival and gaining experience so we will have a better idea of who to send next.

    Too much oxygen? No. Too few oxygen tanks. Send one chemist and a dozen machinists. The job of the first colonists is going to be making things. A structural engineer wouldn’t hurt either.

    Sending enough food to keep them alive is not a big deal because water is available in great quantities on mars everywhere (and we make certain at the landing site before any people land.) Hydroponics are fine to start, but they aren’t going to grow their own food that way, anymore than they do here on earth, so they need live soil with the right bacteria to mix with processed mars soil (they don’t need storage for the excess iron, it becomes storage containers and building material… one of those machinists should have some basic blacksmithing skills they are going to have tons of iron ingots which will be machined to final products. Tools are not a problem, that’s what machinists make.) As iron dust excess oxygen can be absorbed, so even without tanks they can store oxygen (heat to release, h/t to CJ.)

    Mars was made to be colonized. The sooner we get there the better and we could start in less than a decade. Whatever we think they need for solar panels we should quadruple. Because of transportation costs, all personal property will come with a mass surcharge giving every martian (that chooses semi wisely) all the resources they need to start a very good life as long as we find a way to pay their ticket for them ($100m per colonist but rapidly falling over time to perhaps $5m each.)

    If the martians must pay for their ticket it kills off colonization. In two weeks I start my roadtrip to work on that problem.

  10. George Turner says:

    I was just struck by a different idea on the food situation, one that might merit some number crunching.

    Depending on the mission mode (long-duration mission, minimum energy transfer, etc) the crew spends a large percentage of the time in flight, and most probably would be eating stored food (which based on Ensure Powdered Nutrition at 2000 cal/day would weigh 16-oz per man day). The Mars grow room is thus either dead weight on the human flight out or sent on a separate launch, and only during the crew’s stay on Mars does it work toward paying off its extra mass against that 16-ounce per day stored food option.

    Payback might be easier if the plants were used for food and oxygen throughout the entire trip, perhaps in a larger rotating ship or one with much small spinning plant trays. But if you close the loop with in-flight crops, does it make sense to then drop that crop module onto the Martian surface? So my rocket science question of the days is this: If the ship already has the required solar cells, crop support equipment, and lighting, and it gets the crew all the way to Mars, is it better from a mass perspective to leave it in Mars orbit and drop food as needed instead of landing the farm on the surface?

    The baseline Mars One scenario is that the requisite module and supporting solar cells are given a heat shield, parachutes, and landing fuel so they can get all the way to the surface. Since they won’t be coming back up from the surface, the return trip’s mass budget has to add enough stored foods to cover whatever flight mode is used. Landing incurs a large weight penalty, and in the case of the Mars Curiosity Rover the re-entry weight is about 2.67 times the weight of the rover. Going by roughly eyeballing the MIT bar chart of mass requirements, the combined habitation module and biological product system mass 17 tonnes, and I’ll assume the BPS is half of that, or 8.5 tonnes. Multiplying by Curiosity’s mass ratio, that means the BPS would need an orbital weight of 22.7 tonnes, of which 14.2 tonnes is thrown away.

    If you didn’t drop the BPS to the surface, all of that 22.7 tonnes could be devoted to bioproduction. If you keep the final orbital BPS mass at 8.5 tonnes, run the surface food and O2 open loop (but recycling the water), that 14.2 tonnes you saved would translate into 5.3 tonnes delivered to the surface (using the Curiosity mass ratio), and assuming 20 percent of that mass is just storage containers, that results in 4.43 tonnes of consumables delivered. That would support four astronauts for 850 days without even closing the oxygen loop, which could almost triple the 850 day break even point.

    And you still have a farm in orbit for the flight back, and that orbital farm could be resupplied with CO2, N2, water, and Martian soil from the surface with a fairly low mass penalty, not to mention using the moons, so the early ISRU units can stay in orbit, too. This both closes the loop on the mission as a whole while not tying the surface crew to one particular site, because the orbital module can send and receive consumables and resources from anywhere near its orbital plane. This makes it vastly easier to support multiple exploration sites per mission, and after exploring a site the astronauts return to orbit with a load of rock samples, soil samples, and compressed atmosphere. Some of that serves as input back into the biological system, while the astronauts will re-descend with food and oxygen produced from their previous surface site.

    As another benefit, the entire crop growing scheme can be fully debugged and tested in LEO, and the first mission could carry extra raw materials on the assumption that ISRU from the Martian surface will hit an unforeseen snag. If not, subsequent missions can shave that weight. Either way, the flight out and back becomes closed loop with cropping and the only losses are from the surface consumables, and there is no lag time from surface landing until crop maturity (surely nobody is going to re-enter with fruit hanging from plants).

    It presents another set of options to explore in a spreadsheet, of course with better mass numbers for everything, so everyone feel free to start crunching! 🙂

  11. Peterh says:

    If food production is in orbit and food is dropped to the surface as needed, you still need to account for the mass of the delivery system, and delivering replacement material for the greemhouse. Otherwise the greenhouse is limited to delivering less food mass than the mass of raw material sent with the greenhouse. A greenhouse down with the settlement can be hooked into the waste biomass processing to close the loop.

    A farm in orbit to supply crew on orbit or transfering between planets could make sense for ongoing operations. But for the transfer itself not all that much mass of food is needed, allowing for water recycling. Operating a greenhouse on the transfer vehicle is of limited utility, unless we consider the case of a long endurance cycler.

  12. George Turner says:

    That’s the kind of thing I’m wondering, and I’m still playing around with some rough numbers. So far I think the potential mass savings for the mission might be huge.

    Going from the rough guess of a greenhouse mass of 10 tonnes (that could be way off), here’s what I get:

    A pure powered descent from low Mars orbit with no aerobraking would take a mass ratio of about 3.25, whereas Curiosity with aerobraking made it down with a mass ratio of 2.67, but NASA says that method can’t scale up much because of giant parachute issues. But they also threw away the skycrane, and perhaps a better architecture could get the ratio a bit lower, and they were coming in from a transfer orbit instead of low Mars orbit.

    As I said, my numbers are rough, but landing the 10 tonne greenhouse is going to take a mass in low orbital of 20 to 32.5 tonnes. Getting to low Mars orbit with LH2/LOX is going to require a mass ratio of about 4 (depending on modes, etc), so the LEO mass is 80 to 120 tonnes. If you don’t land the greenhouse, the required LEO mass is only 40 tonnes. But once at Mars low orbit, you’ve saved 10 to 22.5 tonnes by not landing it, and so the numbers game continues with food and resource transport.

    Assuming a surface crew of four, you need to deliver about 4 pounds of food per surface day and transport roughly the same mass of soil and atmosphere back up, assuming you’ve closed the water loop on the surface. So for somewhere around 400 pounds transported up and down, you’ve covered 100 days. I’m assuming the oxygen is being provided on the surface, because the minimal Mars schemes assume that fuel and LOX is being produced by ISRU for the ascent or return flight.

    If the ascent/descent craft is using methane/LOX with a vacuum ISP of a Raptor engine (363 seconds), the 4.2 km/sec delta V needed to reach low Mars orbit gives you a mass ratio of 3.25. Assuming your vehicle has a stage mass ratio of 10 (built tough), the payload would be about 24 percent of the launch mass, and if 10 percent of the payload was packaging, the real payload would be 21 percent of the launch mass. The fuel mass is 70 percent of the launch mass, so the fuel weighs 3.23 times as much as the real payload. This fuel is produced on the surface via ISRU, and the rate of fuel production has to match up with the rate of resource consumption, which was 4 pounds per day (depending on closing the O2 loop), giving you a fuel production requirement of 13 pounds per day.

    So assume a transport ship of 1000 lbs dry weight, 3250 lbs wet, delivering 700 lbs of resources per trip, which are consumed at a rate of 4 lbs per day, and flying once every 175 days. The fuel for the first descent is probably launched from Earth, but that’s only 2250 lbs of fuel to low Mars orbit plus the vehicle, or 1.48 tonnes, just 6 tonnes in low Earth orbit instead of the extra 40 to 80 tonnes required to land the greenhouse.

    I haven’t figured in the extra fuel required for the transport to perform a de-orbit burn or return landing, but since it’s much smaller than Curiosity it can depend more on parachutes, or you could recompute the mass ratios for twice the delta V, up the stage mass ratio to about 16, and cut the payload in half while doubling the flight rate to once every 87 days, and producing about 110 lbs of fuel per day.

    One of the keys to the concept would be the greenhouse mass versus the amount of food it produces per day, and the bigger that ratio is, the less sense it makes to try to move or land the greenhouse instead of just transporting its products.

    There are some other mass savings from staying in orbit, some of them potentially huge, such as being able to double the solar cells and keep the grow lights running 24 hours a day (somewhat split between different crops or not depending on the biology of night respiration), while only having 1 hour worth of battery output to cover the night transit, as opposed to requiring 12 hours of battery power on the surface for the same result. Then there’s atmospheric losses, dust losses, angular losses, and the required support structures for surface deployment. The mass savings could end up being much larger than the already large ones from just avoiding the landing.

    One thing I haven’t figured in, however, is radiation shielding. That could be a show stopper for either mission mode.

    I know this all sounds a bit counter-intuitive, because like everyone, I always thought we’d arrive, land, and farm. Eventually we will, but that may not be nearly the optimal way to go about it. We’ve never gone someplace where you have to bring the farm with you. It’s perhaps one of those unexamined assumptions that needs to be run through a spreadsheet.

  13. ken anthony says:

    The initial farm is hydroponic which has almost no mass (inflatable dominates, the rest is ISRU.) Transit food is under 2 kg/day/crew. (and could be a quarter of that as you pointed out.) They should bring a bag of live starter soil (to be mixed with processed mars dirt.) Seeds are natural space travelers (bring lots of variety for experimentation.)

    They will certainly leave a lot in mars orbit. Mars SSTO gives a lot of options.

  14. Doug Jones says:

    The biggest problem for any closed greenhouse is the tiny mass of atmosphere. At one bar and a modest ceiling height, you only have a few kg of air above each square meter of floorspace, vs the roughly ten tonnes available in Earth’s open skies. An ECLSS on the Mono or Mars absolutely MUST have high pressure storage for short-term buffering and liquefaction to allow storage of months worth of food and air to burn with it. At 300 ppm of CO2, a 3 meter high space can only grow a few *grams* of food per square meter, and nitrogen fixing plants will also deplete that component.

    The small atmosphere mass in Biosphere II was the main reason they had such problems with low O2 levels- if they’d had tons of air for each square meter they would hardly have noticed the drawdown.

    Unfortunately, the Red Dragon propellant tanks are not well suited to cryogenic air storage, but the surplus N2O4 and UDMH could be run through a catalytic reactor with ISRU oxygen to produce ammonia. The fixed nitrogen the propellants represent is a tremendously valuable resource and would provide fertilizer for decades.

    Hydroponics systems require replenishment with concentrated nutrients and can’t recycle crop waste; on the other hand aquaponics (using fish hatched from cryopreserved fertile eggs) can be part of a composting-worms-duckweed-fish-growbed system, with almost no waste. Add rabbits to eat stems & leaves and you get four drumsticks apiece.

  15. George Turner says:

    The X-15 ran on ammonia/LOX, and the Russians are experimenting with a mixture of 30 percent acetylene in ammonia as a direct replacement for RP-1, giving about 10 seconds higher ISP than RP-1 while solving several problems. NASA spaceflight thread

    In an RD-161 (development discontinued) that should give an ISP of 370 seconds, whereas a Merlin should see maybe 350 seconds. A different oxidizer would of course lower this, and red-fuming nitric acid might give an ISP of 340 seconds based on some Russian RP-1/RFNA engines.

    Once landed on Mars, the acetylene should boil off long before the ammonia, making fractional distillation quite simple. Then the ammonia is mixed with the nitric acid to make ammonium nitrate, and that is used to fertilize the plants.

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