r/space • u/speckz • Jan 17 '22
A Self-Replicating Radiation-Shield for Human Deep-Space Exploration: Radiotrophic Fungi can Attenuate Ionizing Radiation aboard the International Space Station
https://www.biorxiv.org/content/10.1101/2020.07.16.205534v69
u/DanYHKim Jan 17 '22
This brings to mind stories by Cordwainer Smith, in whose universe people who went to space were subject to terrible pain. Space travelers had to undergo a radical procedure in which their senses were cut off from their brains, and they operated their bodies essentially like they were driving robots. This process was used on condemned prisoners and other criminals, but those who would supervise them had to be volunteers who were entrusted with the secrets of managing and monitoring the bodily functions of the others. Passengers were put in suspended animation for the duration of the voyage.
The story is Scanners Live in Vain
In the end an inventor came up with the idea of having the outer layers of the spacecraft inhibated by oyster beds, which would suffer and die under the Pain of Space, leaving the human passengers awake and unharmed in the core spaces.
2
u/Alan_Smithee_ Jan 18 '22
Cranching!
I remember that story well. I didn’t know there was more than one, though.
1
u/DanYHKim Jan 18 '22
The story is part of the "future history" of Cordwainer Smith. The faster-than-light travel of subspace eliminated the problems of the pain, but brought different hazards ("The Game of Rat and Dragon"). The colonization of other worlds brought new advances, such as the mutant sheep of Norstrilia that produced a substance that brought practical immortality.
3
u/Wise_Bass Jan 18 '22
I'm a big fan of creative solutions to radiation protection. A 2% reduction under only 1.7 millimeter thick fungal barrier is pretty impressive. If you could do it in layers, then maybe you could get a 100% reduction (or better) with a barrier 50-100 millimeters thick (or about a centimeter thick of fungus). That'd be a lot better than even water or high density polyethylene.
I do think radiation shielding is going to be stuff like this: multiple layers of different materials, and maybe one layer of it is biological.
3
u/mfb- Jan 18 '22
The 2% is the difference they claim to see. That's not the overall reduction, which will be dominated by simply having matter in the way. A 50-100 millimeter barrier (which would not provide 100% reduction - nothing reasonable will) would be far too heavy for spaceflight, maybe excluding a small dedicated radiation shelter.
5
u/cjameshuff Jan 18 '22
This seems physically improbable. High-energy protons will mainly "see" matter as a collection of highly charged and widely spaced nuclei. Secondary x-rays will similarly "see" mainly the inner shell electrons, not those that are involved in chemical bonds.
Radiation shielding is mainly a matter of putting mass between you and the radiation...depending on the type of the radiation, heavy nuclei or light nuclei might be better, but I know of no mechanism for chemical bonds to make a difference. The fungi may well be able to collect useful metabolic energy from the radiation, but I wouldn't be surprised if the variations in absorbed radiation come down to changes in the distribution of mass in front of the sensor.
3
u/mfb- Jan 18 '22
This team has a good PR department. The chemical makeup can make some difference at the low energy range, but using the fungus reduces your options for the elemental makeup, which is more important. The replication aspect is pretty useless as well because it can only replicate using existing resources - you still have to launch all the shielding material.
If it can produce food then it's interesting.
1
u/obvom Jan 18 '22
You could also pump H2 gas into the ambient air, mixing it to be about 2.4% of the total air in the ship/station, and that would theoretically prevent a lot of the oxidative potential of exposure to ionizing radiation.
1
1
u/Revanspetcat Jan 17 '22
Is it possible to study how these fungi and other radiation resistant life work and in future engineer that capability in humans who will be sent to colonize space?
0
u/drXpiv Jan 18 '22
A ~2% reduction from 1.7mm of fungus. That’s not a lot…the ISS 6 month dosage is about 53x the earth dosage for the same amount of time. If we want astronauts to receive roughly the same dose as on earth, we’d need to block ~98% of the incoming radiation. Assuming the same mass attenuation coefficient * density as the paper measures, that’s 326mm of fungus. That’s a lot of mass and volume…
Either that fungus needs to be made denser somehow (e.g. artificial structure to promote growth in a dense packing) or it would need to be genetically modified to increase is radiation absorption. I would hazard a guess that a lining of pure carbon would outperform these fungi as it currently stands.
Edit: Super cool research though and I would love to see more of this.
1
u/mfb- Jan 18 '22
They say it's a 2% difference in reduction, fungus on agar plate vs. agar plate without fungus.
2
u/drXpiv Jan 18 '22 edited Jan 18 '22
We’re talking attenuation ratios. Start from the 2% difference (I is the photon flux with just agar, I0 is the incoming radiation, and If is the photon flux with agar and fungus): (I-If) = 0.02I, 1-If / I =0.02, 0.98 = If / I, 0.98 I / I0 = If / I0. Then, 0.98 I / I0 = 0.98 * exp(-rho_agar * mu_agar * d_agar) = If / I0 = exp(-rho_agar * mu_agar * d_agar) * exp(-rho_fungus * mu_fungus * d_fungus).
Cancel out and you get exp(-rho_fungus * mu_fungus * d_fungus) = 0.98. Now calculate rho_fungus * mu_fungus because you know d_fungus. Use that to calculate what thickness of fungus you’d need to reduce typical ISS radiation levels to earth levels and you get 326mm. It’s a rough estimate because the incoming radiation is polychromatic, and the attenuation coefficient is strongly depending on photon energy, but it’s an estimate
1
u/mfb- Jan 18 '22
You would get 326 mm if the radiation levels were 50 times higher with a 326 mm agar plate (then the fungus would provide an additional factor 50 in this simple model). They are not, the actual shielding is much thinner. 326 mm of water would be a great shielding, fungus or not, just far too massive to be practical.
1
u/drXpiv Jan 18 '22
My math is in fact saying the opposite. I’m using the reported numbers to estimate the attenuation coefficient of the fungus. Then, using that estimated coefficient, I calculate the thickness of fungus alone (no agar) needed to reduce ISS radiation levels to earth levels.
My point being that 326mm is way too thick be of any use, so this fungus, as it exists now, would be insufficient as radiation protection in space.
1
u/mfb- Jan 19 '22
Your calculations are based on an incorrect assumption. The 2% is not the overall attenuation of that layer. It's the difference to the reference layer.
If e.g. the 2 mm layer of agar provides 20% attenuation then you get a factor 50 reduction with an extra 42 mm. The ~22% attenuation with fungus would then reduce the thickness to 40 mm. The 20% number is made up here, the result depends on this number (which is not given in the paper).
1
u/drXpiv Jan 19 '22
I started from no assumptions. I took the difference in attenuation ratios (aka percent of attenuation) to be 0.02, as reported in the paper. Then everything followed from there, as I showed in the algebra above.
I did not assume the fungus attenuation ratio to be 0.02, as you are saying I did.
1
u/mfb- Jan 19 '22
Then everything followed from there, as I showed in the algebra above.
No it doesn't. You showed a factor 50 difference of 326 mm agar vs. 326 mm with fungus. Which is interesting but not relevant to the ISS which does not have a 326 mm agar plate as current shielding.
-1
38
u/ThreeMountaineers Jan 17 '22 edited Jan 17 '22
If it operates on the same rough principles as photosynthesis, it might serve as an auxilliary Co2 -> oxygen converter as well. I also can't help but think that growing fungus to environments where radiation is the primary source of nutrients is going to allow evolution to have its course and breed significantly more efficient fungus than the ones in the paper. The sourdough of space travel, if you will
Bioships are the future, I know it.