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Comment by barbegal | Hacker News Reader

I am skeptical that this fungus absorbs radiation significantly more than the equivalent amount of water would. The paper [1] isn't very clear about possible inaccuracies in the results and I don't understand why this experiment hasn't been repeated down on Earth. The mass attenuation coefficient of the fungus is 0.234 cm^2/g at 100MeV whereas water is 0.0166 cm^2/g according to this paper [2].

[1] https://www.biorxiv.org/content/10.1101/2020.07.16.205534v1....

[2] https://apps.dtic.mil/dtic/tr/fulltext/u2/a278139.pdf

Edit: I made a mistake in this comment, see child comment for correction.

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Reading the paper again, I made a mistake in my comment above. The mass attenuation coefficient was at 10keV not 100MeV. Water has a mass attenuation coefficient of about 5cm^2/g at 10keV.

Table 1 [1] in the paper shows the true comparison with water at 100 MeV where it can be seen that there is not a large difference. On a weight basis stainless steel outperforms the fungus.

[1] https://www.biorxiv.org/content/10.1101/2020.07.16.205534v1....

Maybe it’s because you have to ship stainless steel from Earth. Maybe the mass of the fungus can be grown from CO2 from respiration. The carbon originally coming from food, which has to be shipped up. Lots of maybes, but you know, maybe...

To grow fungus from CO2, don't you first have to grow a plant then let the fungus eat dead plant? Plants require (heavy) equipment to support them.

If it can photosynthesise (on gamma rays no less), then perhaps not. Mold can grow on concrete walls and stuff, so not sure what it needs.

It sounds like this fungus only produces energy, and doesn't fix carbon like photosynthesis does.

Mold growing on concrete walls is actually living off the dust and other organic debris that accumulates on the surface if you don't clean it.

> Maybe the mass of the fungus can be grown from CO2 from respiration.

That's not a thing. Fixing carbon to a usable form [0] using "general biological energy source" to the carbon pool is extremely difficult (there are only four and a half, counting c3 vs c4 as a half, pathways known) and requires complex machinery to achieve.

[0] assimilating carbon dioxide in general is not difficult, even humans do it but it does not enter the general carbon pool and is effectively only transiently converted out of CO2, and net does not contribute to biomass.

Zeolites can do this. https://en.m.wikipedia.org/wiki/Zeolite

Either you ship steel, or you ship biological material - you're shipping things either way. (And if you can do ISRU, then steel or just plain cast iron is available)

Steel doesn't reproduce though.

Reproduction doesn't create matter ex niliho, either. And in space, organizing the matter is far easier than getting the matter in the first place.

I wonder if material degradation factors like neutron embrittlement would tip the scales in favor of a fungal barrier at longer timescales.

>> it could be shown that the melanized fungus C. sphaerospermum can be cultivated in LEO (Low Earth Orbit), while subject to the unique microgravity and radiation environment of the ISS.

I believe this "small scale" experiment was meant as a "proof of concept" to illustrate the idea whether this could be done in house in adverse conditions (unlike Earth's conditions) and could be a potential long term solution for radiation attenuation. I would hope that these somewhat promising results would allow them to conduct a large scale experiment.

still worth for the conversion of radiative energy to biological activity

nuclear waste may become green :)

Not really, almost all the radiation is converted to heat just like in any shielding material.

hum isn't it more efficient to divert it into "productive" chemical active than average heat (then used for whatever) ?

Well technically it already is pretty darn green in that the energy system concentrates its waste into tiny generally well-contained packages that have, per TWh generated, a relatively miniscule negative impact and footprint on the biosphere.

I recognize this is controversial but the numbers are pretty solid.

Totally true and nothing disappoints me more than the push away from nuclear energy

totally untrue they dump the western nucular waste in front of the Somalian coast.

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