Enhanced Gravity Tractor Paper at the IAA Planetary Defense Conference

I’ve noticed that very few people seem to understand the concept of the Enhanced Gravity Tractor planetary defense technique that the ARM Option B approach plans on demonstrating. A friend recently forwarded me a great paper describing this concept that was presented last month in Italy at the IAA Planetary Defense Conference, that provides a good introduction to the concept:

IAA-PDC-15-04-11 Enhanced Gravity Tractor Technique for Planetary Defense

The high level version is that by collecting mass from the target asteroid, you can enhance the diversion speed of an asteroid by 10-50x or more compared to using a normal gravity tractor without local mass augmentation. This means that even for an Asteroid Redirect Vehicle with a capture mechanism about the size Altius analyzed in its ARM BAA study, you could redirect an earth-crossing 100m class asteroid with <1yr notice, and a 150m diameter (Tunguska-class) asteroid with <2yrs.

There were a bunch of points made in the paper, but a few of the more interesting ones are:

  1. Because an enhanced gravity tractor works via gravity, you could use it to divert debris from an unsuccessful nuclear diversion attempt.
  2. You can speed up the process by putting multiple EGT spacecraft into a halo orbit around the asteroid simultaneously.
  3. The EGT doesn’t necessarily require boulders on the target asteroid. If the redirect spacecraft has the ability to scoop regolith for instance, you could use regolith or smaller rocks instead of a boulder extractor system.

There’s a lot more to it than that, but I wanted to put this article up there because I think most people following ARM, especially critics, could benefit from access to the article.


Posted in NEOs | 5 Comments

Taong Boondocks Post on Service

For today’s installment of my month of blogging, I did a post on Taong Boondocks (my other blog) about Service and the Atonement. Advanced warning–it’s an LDS religious philosophy piece, so if religion isn’t interesting to you I should be back to spacey topics tomorrow.

Posted in Uncategorized | 1 Comment

Light Reading Recommendations for House CJS Appropriators

Some tweeted comments from the recent House Commerce, Justice, and Science budget markup meeting gave me some ideas for light reading for our esteemed House Appropriators.

Specifically, Jeff Foust (@jeff_foust) of SpaceNews tweeted that:

This made me think they could possibly enjoy the following two old business books (or at least the Cliff Notes versions):

  • The Goal — This 1984 classic introduces the Theory of Constraints, which demonstrates that applying resources to parts of a process that are not the bottleneck rarely helps improve throughput. Like for instance providing more funding to SLS and Orion when the bottleneck is the ESA-developed Orion Service Module, and the lack of manned spaceflight payloads being funded.
  • The Mythical Man Month — I haven’t actually read this one, but like most people and the Bible, I can paraphrase some general points. One of the great insights from this book is that it’s often not possible to expedite a late project by throwing more people and resources at it. Or as von Braun said: “[Crash programs] fail because they are based on the theory that, with 9 women pregnant, you can get a baby a month.” A relevant example of this is that throwing more resources at SLS and Orion in the hopes that maybe they’ll still fly EM-1 in 2017.

Anyhow, I just wanted to provide these recommendations in case any readers happen to be friends with any of the House Appropriators and didn’t know what to get them for Christmas this year.

Posted in NASA, Politics, Snark | 3 Comments

Upcoming Milestones and a Month of Blogging

I just realized the other day, that we’re rapidly approach the 10 year anniversary of my first post on Selenian Boondocks. The big day will be on June 16th, 2015. In celebration of that milestone, I’m going to try to do a blog post a day for the next month. Some of those posts may be short, and may be links to blog posts I do on the ASM blog or Taong Boondocks, and if I get desparate, I might even do a few reposts or updates of some of the more popular articles from the past. But I want to try and do something every day over the next month.

In case you’re interested, the next month or so has a few other interesting milestones:

  • Tomorrow (May 16th) marks my one year mark on DuoLingo studying Spanish. I’ve had to use the streak saver a handful of times (~4 or 5), but my streak is currently at 364 days. I’m still a beginner, but can at least read signs in Spanish reasonably well.
  • June 4th is the one year birthday of our youngest son, Andrew Perigrin (“Pippin” or “Pip”) Goff. He’s a lot of fun. Probably our happiest baby so far.
  • July 2nd is the 5 year anniversary of incorporating my space robotics and technology startup, Altius Space Machines. We’ve been primarily bootstrapping since then off of a mix of government and commercial contracts, and sometime in the next month we should cross the $2M cumulative revenue mark for the company. That’s slower than I would’ve liked it, but we’re starting to gain some momentum, and finally in a new office in Broomfield, CO. BTW, this is the main reason why I don’t blog as often these days as I used to. That and four little boys and being recently called as an Assistant Scoutmaster.
  • July 6th is the 5 year anniversary of leaving my former startup, Masten Space Systems, to start Altius full-time. I’m really glad Dave roped me into helping him start Masten. It’s been great seeing how much they’ve accomplished since I left. I can’t repeat enough how proud I am of where they’ve taken things over the past five years. They’re cashflow positive off of flying EDL flights for NASA and commercial companies under the Flight Opportunities program. Last I heard they’re over 20 employees, they’re running the “black horse” team for the DARPA XS-1 program, and they’re about to start free-flying two new vehicles. Not to mention they have a vertical take off and landing rocket vehicle with >220 flights under its belt that I got to help build. :-)
  • August 8th is the big 35 for me, and the 13th anniversary of getting back from my mission in the Philippines.
  • August 23rd is Tiff’s and mine 12th wedding anniversary.

Lots of milestones. Now let me see if I can actually keep up with the blog a day promise…

Posted in Administrivia | 3 Comments

Asteroids as Transportation Hubs


This is a sketch from a post I did in 2009  about moving asteroids using their own rotational energy to sling ISRU mass  to change their orbit.


With Jons’ last post, I got to speculating about other ways of getting mass from an asteroid back to Earth. What if the exploring spacecraft carried a tether to the asteroid that was long enough to serve as a beanstalk. Instead of carting the selected boulder(s) all the way home, the beanstalk is used to sling a number of samples to Cislunar space to be caught by some TBD craft.

Instead of the thousand ton boulders slung in the original post, ten or so tons per throw would send a sizable mass to explore and exploit close to home while leaving the spacecraft in the field for a continuing mission. While as in the previous it would be necessary to wait for launch windows to use the tether,  the time between arrival and window could be spent exploring the body in question and organizing multiple throws. When the window opens, the ten (or one or thirty) ton samples could be sent Earthward every time the asteroid rotates. A four hour asteroid rotational day would give six launches per Earth day. A window a week long could have forty or so samples heading home at once.

If the asteroid is considered explored by that time to the limits of the available craft, it is time to head to the next target. One way of doing that would be for the spacecraft to climb the tether to well past astrosync orbit to a point calculated to sling it to the next body to be explored. At the right time, the tether is cut loose at the asteroid end to send the vehicle and its’ tether to a new little unexplored world. Once there, the cycle is repeated. It would seem that the craft could explore and exploit indefinitely without running out of propellant.

For a second phase of exploitation, tethers are left attached to the asteroids for use by future visitors. Eventually, spacecraft could visit dozens of rocks during an operational lifetime to prospect for different substances or to test new techniques in a variety of locations.

Certain asteroids would be exceptionally useful in a third phase if they proved exceptionally well suited for transportation hubs. Instead of slinging small robotic prospectors to other rocks, long beanstalks could relay humans and cargo to Mars and other points of interest throughout the inner solar system.

Posted in Uncategorized | 12 Comments

Up in ARMs for No Good Reason

While there has been some slightly more positive discussion about the NASA Asteroid Redirect Mission since my previous blog post and SpaceNews Op-Ed, there have still been a steady stream of criticisms and suggestions of alternatives to the ARM mission being discussed lately. I’ve always been a bit of a knee-jerk defender of the underdog, and I still don’t think ARM is being given a fair shake by many in the space policy community, so I want to take the opportunity to respond to some of these criticisms and alternatives. And by respond, I don’t mean just dismiss–some of the suggestions have real merit, and could lead to ways to improve the existing ARM mission.


  1. We should be looking for asteroids not trying to redirect them — This criticism is that before sending a mission to an asteroid, we should be making more of an effort to find the vast majority of NEOs that we still haven’t identified. I actually agree that a strong effort at identifying more of the NEO population would be money well spent. As I pointed out in a previous post based on a talk by Josh Hopkins about LM’s Plymouth Rock mission concept, more knowledge of the NEO population and orbits gives us more options and can only make missions like ARM and others better over time. I don’t think this should preclude doing ARM as well, but finding ways to invest more effectively in this area would be useful. Some suggestions for how we could do better here range from traditional approaches such as funding a NASA asteroid hunting mission or  doing a competition for industry provided asteroid finders, to providing matching funds or a free rides for more commercial missions such as what Sentinel and/or the prospecting spacecraft  Planetary Resources and Deep Space Industries are developing, to potentially offering a bounty for detection and verification of new asteroids. It doesn’t have to cost billions, but spending a bit more money in this area is likely to make ARM better, and increase our odds of finding dangerous asteroids with enough time to do something about them.
  2. OSIRIS-REx is already doing this — I’ve heard people criticize ARM because the OSIRIS-REx mission is already going to be returning samples from an asteroid before the ARM mission is flown, and thus we don’t need another mission. I find this argument as silly as Obama dismissing the Moon with his “Buzz has already been there, done that” argument. Just as the Moon is a world the size of Africa, and you can only learn so much from a half-dozen landing missions, how much are we really going to learn about the millions of asteroids in the NEO population from a few hundred grams of materials returned by a handful of sample return missions? How much do we really know about the consistency of material composition even within one single decent-sized asteroid? What are the odds that even two C-type asteroids are going to be identical enough that additional samples wouldn’t be worth it?
  3. We need a large number of samples, not a large sample — I partially agree with this argument–diversity of samples is important, but so is having enough quantity to actually be able to do useful ISRU experimentation. The multi-teaspoon sized samples provided by current missions might provide you with some idea of the chemical composition of at least that part of a given asteroid, but learning how to mine asteroids (and if we can do so in a way that makes economic sense) is going to take larger samples. One possible compromise that could give you the best of both worlds might be a multi-lander/grasper ARM concept. Instead of having one big 4m diameter boulder grasping system, ARM could potentially do 6-7 smaller (~2m) separable grasper/landers, attached to an ESPA-ring like structure, and the spacecraft could also possibly visit more than one asteroid during the mission. As commenters have pointed out previously, there are actually relatively low-delta-V multi-asteroid tours that can be done that go from Earth to several interesting locations along the way before returning to earth. That way you can get sizable samples and variety, maybe 1-2 carbonaceous chondrite boulders, throw in a nickel-iron sample or two, and then one or two samples from another asteroid types. While this may sound a lot more complicated, NASA has already demonstrated multi-asteroid rendezvous with missions like Dawn, and building 6-7 copies of a lander grasper system would actually mean that a lot of the complexity is offset by larger efficiencies of scale–with a Prospector-like Option B grasper mechanism, you’d be making dozens to hundreds of most individual piece parts instead of the one or two that you often see for more traditional science missions. If I get more time, I’d like to flesh this idea out in its own blog post, but I wanted to get it out there publicly in case I can’t find that time.
  4. You shouldn’t pick the boulder just on its pluckability — One concern was that the boulder would be picked entirely from a standpoint of ease of extraction. I agree with this concern wholeheartedly, but NASA has already indicated that they were are planning to include at least a basic sensor suite to help with picking an interesting boulder, not just an easy one.
  5. You should bring the boulder back to Earth Orbit instead of DRO, because that’s just make-work for SLS/Orion — This one also comes up a lot. The fact that ARM is bringing the boulder back to DRO instead of LEO is seen as somehow indicating that this is all just a make-work stunt. But the more you study the problem, the more DRO seems like a reasonable choice. Spiraling in to earth orbit from escape velocity takes >5km/s of delta-V with a low-thrust system, on top of all of the other . This would require either a refueling or two, or a much bigger spacecraft (about 2-3x the size), and would take a really long time. High Thrust-to-Weight SEP stages can take 6 months to 1 yr to spiral out from LEO to escape. But with a 40-80 tonne boulder attached, the T/W ratio for the return spiral would be 5-10x worse, which would mean 3-10 years spiraling through the van Allen Belts. If you use aerocapture/aerobraking instead, with such a large mass, you would need either a large aerobrake, a lot of time, or something like the magnetoshell aerocapture technology we’ve been supporting MSNW on. I’m obviously not opposed to that last option, but this would be a non-trivial additional system development. Plus, even if you could magically snap your fingers and get an asteroid into LEO, there would still be challenges. An asteroid in LEO would be easier to visit but would also be a debris hazard (especially as you try to mine it and accidentally knock dust or rock chunks off or it), would have to deal with a much worse micrometeorite/orbital debris environment than it would in DRO, would be unlikely to have enough T/W to dodge a detected conjunction with other dead space objects in LEO, and would require constant propellant for reboost. It’s not an entirely impossible, but it’s not as much of a slam-dunk as some seem to think.
  6. Grabbing a boulder has nothing to do with planetary defense — This is one of the more ridiculous statements I’ve heard repeated by otherwise very intelligent people. The reality is that unless you’re going to use nukes, the gravity tractor is probably one of your better bets for asteroid deflection. And because the mutual gravitational attraction is proportional to the masses of the two objects multiplied together, there’s a big benefit for being able to increase the mass of the spacecraft using local mass. What better way is there to rapidly increase the mass of your spacecraft via in situ materials than to grab one or more big boulders off the asteroid?
  7. We should do ARM just minus the whole going to an asteroid and bringing a sample back thing — That’s like saying we should go to Mars but without that whole going to Mars thing. I think people are laboring under a false belief that the boulder grasping mechanism is most of the cost of ARM–it probably isn’t. The spacecraft bus and human spaceflight follow-on mission are likely a much bigger chunk, and NASA has already indicated they’d like to do those even if ARM was canceled. Canceling the grasping mechanism is unlikely to save you much at all–maybe the equivalence of a CRS mission or two, or a few months of SLS or Orion development. Spending the vast majority of the cost of the mission but without actually achieving useful exploration or ISRU development would be a waste. Why do people think that play-acting at being astronauts out at DRO without an actual useful mission for them to be performing is somehow more grown-up than doing actual exploration and potential ISRU research?
  8. We should skip the asteroid and go to Phobos instead — This is one of the best alternatives (not surprising considering the source–I have a ton of respect for Wayne Hale), and while I think it’s not the best option, I wouldn’t be heartbroken if ARM was refocused in this way. One of the selling points of ARM was that it is relevant to future Phobos/Deimos missions–the ARM spacecraft can and should be designed so that it can be refueled and “re-clawed” and used for another destination. The marginal cost of a Xenon tank and another copy of the claw is going to be trivial compared to the overall mission development costs, and there are tons of good reasons for an ARM-like mission to go to one or both of those moons. We didn’t explicitly analyze the case of grabbing a boulder from Phobos/Deimos, but a NASA Langley team did, and found that you could get a 1-2m diameter boulder off of them using the existing Option B hardware–notice this is the same size as the multi-lander/grasper concept mentioned above. But by skipping out on the asteroid first, you would lose the ability to test gravity tractor techniques, which could be important, and asteroids are also interesting in their own right. So I’m torn. I’d rather do both.
  9. We shouldn’t do anything that isn’t directly on the quickest path to Mars — I probably won’t convince Zubrinites, but it turns out we have this whole Solar System that doesn’t just consist of Earth and Mars. If manned Mars exploration was something we could do quickly, within NASA’s existing budget, or if there were no other interesting or useful destinations along the way, it might be one thing. But even the committee members who are advocating for this have admitted we don’t have the money to do a manned Mars mission in the next 25 years without significant increases in NASA’s funding. While it has been poorly marketed, Flexible Path wasn’t just about “doing asteroids first” or doing them instead of the Moon or Mars. To me the underlying point was that even if Mars is the long-term goal, we should find ways to do interesting exploration along the way to Mars, even if some of those destinations involve slight detours along the way. When you’re talking about a destination over 25 years out, acting like a 3 month delay is somehow insufferable is flat out ridiculous.
  10. We should just fly an SEP module to Mars and back instead of ARM — While the concept of skipping the asteroid and going straight for a Phobos or Deimos boulder return option actually made some sense–I think the concept of building a big SEP just to fly out to Mars and back is plain ridiculous. We’ve already demonstrated the ability to use SEP systems to do multiple rendezvous with celestial bodies, as mentioned earlier. SEP technology is likely going to shift so much over the next 25 years that the only good reason to spend a lot of money building and flying a demo SEP system now is if we’re using it for something useful like ARM. Building an ARM-class SEP system and just flying it around with no greater purpose seems like a waste to me. And as mentioned previously, you’re not actually saving that much money by ditching the whole grasper thing.

I could go on, and there are other positive suggestions I could provide, like using a COTS model on the SEP module to make something that gets us the experience we want while still being commercially relevant. But I wanted to provide some more thoughts for the ongoing conversation. ARM may not have very good odds of being funded to completion, but it’s not because the arguments against it are actually all that sound.

Posted in NASA, NEOs | 11 Comments


Sometimes the ideas I throw out are obscure and hard to communicate, and sometimes they are so blindingly obvious that they have been rehashed many times in the decades past. Since I have no feel for which is which, sometimes I throw an idea to the wolves (that’s you) to see which it might be, and also to see if some of the follow ons are equally obvious, or not as it may be.

In my last post on the small tetherocket, the idea was somewhere in the middle. This is one of the possible follow ons that I have thought about before, but only decided to write out as my reaction to some of the feedback in comments.

turbinozzleOnce again my cartoon may be a bit difficult to read. The black lines at 3,000 m/s are expansion nozzles spinning on a tether complex as in the last post. The small rocket inside the curves is fixed relative to the ship with a suggested exhaust velocity of 4,000 m/s retrograde to the ship. The 4,000 m/s exhaust encounters the spinning nozzles with a closure rate of 7,000 m/s. The exhaust bends nearly 180 degrees in the moving nozzle with the gasses retaining the 7,000 m/s velocity relative to the turbinozzle. The gasses exit the turbinozzle at 7,000 m/s nozzle relative which is 10,000 m/s ship relative.  Net Isp just over 1,000.

I suggested 4,000 m/s exhaust velocity for the H2/O2 rocket as it would likely have a low expansion ratio to fit the envelope. I suggest that the near 180 degree turn in the turbinozzle channels would cause shock losses that would cancel any expansion gains from the nozzles.  I believe that the thrust/weight ratio would remain in the 1 m/s range for the bare engine.

This would retain the capability of using any fluid reaction mass available in the solar system from CO2  to water to impure methane if that is available ISRU. The rocket engine would need changing out to a steam engine using whichever fluid is available for a likely Isp in the 500+ range if I see the reactions correctly.

One of the comments suggested beamed energy and hydrogen only as a superior alternative. Nothing any of us said would preclude using beamed energy to drive the reactions. It would solve a number of problems with onboard power if available. Hydrogen may or may not be the reaction mass of choice. The tankage mass and handling properties may well make it second best even if it happens to be available at a particular location.

On one end of the conceptual capabilities is the possibility that I am pessimistic in the capabilities suggested. A larger envelope for the fixed expansion nozzle may make it  possible to get 4,500 m/s exhaust velocity from the fixed rocket which would add 1,000 m/s to the final exhaust for a total of 11,000 m/s exhaust velocity. It may also be possible to recover the energy from the turbinozzle heating to a higher velocity exhaust which could possibly add another 1,000 m/s to the final gas velocity then totaling about 12,000 m/s.  Hopefully the speculative possibility of Isp=1,200 will have a qualified person of two running a few simulations for the entertainment value.

Posted in Uncategorized | 5 Comments

Small Tetherocket

Some years ago I posted an idea for combining tethers, rockets, and nuclear power to build an engine with very high Isp for orbital transfer operations. 750-850 seconds Isp with LH2/LO2 seemed and still seems possible. I am posting a follow on to that idea with some modifications suggested by commenters and some of my own.


The original post is at     http://selenianboondocks.com/2008/10/tetherocket/


In this cartoon, the spiderweb structure is a connected tether complex inside a pressure disk. It is powered up to 3,000 m/s by the onboard nuclear or solar power with the spin maintained by continuous power input.  The little angles on the tether tips are the throatless diverging combustion chambers. The LH2 and LO2  are sprayed into the path of the combustion chambers and both mixed and ignited by the 3,000 m/s impact. The pulse detonation burn will exit the combustion chambers at close to the 4,500 m/s characteristic of an LH2/LO2 engine in vacuum relative to the moving combustion chamber.

The small combustion chamber  expansion ratio is partially compensated by the impact heating and pulse detonation in the initial chamber. The near 4,500 m/s exhaust velocity is relative to the moving combustion chamber though and has a vehicle relative velocity of nearly 7,500 m/s. The exhaust then enters the single fixed high expansion ratio nozzle to finish expanding to as near vacuum as possible. The net exhaust velocity should be in the 8,000-8,500 m/s range.

I still see the T/W as being about 0.1 or 1 m/s acceleration with the bare engine and probably about a tenth of that including  vehicle mass. 100 cm/s would go from LEO to Lunar Transfer Orbit in about half a day using about 1/3 of IMLEO to do it.

Higher T/W than ion engines. No radioactive exhaust as in nuclear thermal and higher propellant densities to boot at similar net Isp. Switch to methane/Lox or any other bi-propellant  by changing two low pressure injector elements. Able to use inert gasses from ISRU anywhere in the solar system for Isp in the 450-500 range using the mechanical drive alone.

Posted in Uncategorized | 35 Comments

Precursor to Station

The comments on the torus station post made it clear that I had skipped steps in suggesting a specific station type. One step is the investigation of exactly how many RPMs are acceptable for a working orbital facility. The acceptable RPMs dictate the length of the station arms to achieve a given gee level. The required arm length or torus diameter needs to be known before design starts, and long before construction starts.

I suggest that an initial investigation on the ground could be a 10 meter radius unit with a 3 meter inclined floor around the circumference. There would be a bit over 190 square meters of available floor area when the unit is spun up. The floor area would be divided into offices, bathrooms, kitchens, bedrooms, and other requirements as needed.

The unit would be spun up to the design RPM for that particular design. There would be one acceptable RPM for any fixed floor angle with several different units for different investigations. This would be terrestrial construction and relatively cheap compared to anything launched which would make multiple units on the ground affordable compared to launching sub-optimal stations.

The unit is spun up to design RPM with the intention that it will spin continually for several months at a time. Several shifts of investigators work in the facility on short and long term ‘missions’. Some works 8 hours plus lunches and go home at night exiting through the hub without stopping the unit. Entry, exit, and transition through the spokes would be part of the experiments. Others stay for 30 days straight, while yet others do business visits of minutes to hours.

The purpose would be to determine whether 10 or more RPM can be adapted to in a working environment. I would see the experimenters as being  perhaps one department of a company or government facility totaling between 20 and 100 people on a near continuous basis plus many visitors. The quality of an individuals work compared to their normal performance in regular environments would be a good baseline to prove/disprove the possibility of very short radius stations for people in high stress and workload environments as during a space mission.

The long term investigators would exit fairly often for family functions and such which would be the  spin equivalent of going to the microgravity sections of the station or an EVA. The ability to conduct the investigation without missing the kids recital or your wedding anniversary would make it possible to get long term volunteers.

After determining the acceptable RPMs for people in a real working environment it wold be much easier to design a real working station. A 5 meter spin radius in orbit is a totally different animal than a 1000 meter radius. If the ability to adapt to high RPMs eliminates 99% of the population, then there would still be about 3 million people in this country to select from plus several times that number world wide.

Posted in Uncategorized | 17 Comments

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

Posted in ISRU, Space Settlement | 15 Comments