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Comment by jxcole | Hacker News Reader

IIUC most of the mass required to build plants comes out of the air (CO2). Of course, any astronauts wanting to utilize these fungi will have to take some amount of other resources with them.

The most important measure for any radiation shielding in space is weight. We have great technology for blocking all radiation today: lead plating. This is obviously way to heavy for space. Alternative suggestions have been to surround the astronauts with water which presents a lot of challenge in terms of plumbing and weight. Having the walls covered in fungi may actually be a much lighter option, I certainly hope the idea is well considered.

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> IIUC most of the mass required to build plants comes out of the air (CO2).

Fungi aren't plants, though.

edit: they're heterotrophs - they get their food from more complex materials than autotrophs, which generate their raw material largely from carbon extracted from the atmosphere.

> edit: they're heterotrophs

Except not these ones! These are autotrophs fungi, they do some kind of photosynthesis (it's absolutely not the same metabolic path, though) gaining their energy from gamma rays instead of food.

Edit: The above comment is wrong, I though autotroph vs heterotroph was about energy input (as a matter of fact I'm very convinced it was how my college teacher explained it) but from wikipedia it looks like I'm wrong, and such fungi would be classified as Photoheterotroph[1]

[1]: https://en.wikipedia.org/wiki/Photoheterotroph

Yes, but they're still fungi. They might be extracting some amount of energy from radiation, but they still get most of their energy (and cellular raw material) the old fashioned, biological way. It's not like they suddenly evolved replacement pathways to synthesize all the products they need.

For fungi, the carbon source is actually even more straightforward than with plants: we can just feed them biowaste. Depends on the species of course, and probably requires some treatment to not encourage growth of less desirable species instead. If they turn out to be edible, this could prove to be ideal.

Don't fungi "breath" out CO2 as well, I think I remember reading that somewhere. That might be an issue in space.

Lead does not block "all radiation". Here's a great video that explains common types of radiation and what kind of materials are effective at blocking each of these types of radiation: https://www.youtube.com/watch?v=iTb_KRG6LXo

There's plenty of radiation that we have no effective way of blocking, like neutrino radiation.

Ability to block/attenuate radiation is proportional to interaction probability which is generally also proportional to biomedical risk: ergo, if we can't block it, we don't care about it.

Short version: sometimes it's not the bullet that kills you but the spray or ricochet. There are plenty of types of radiation that you want to block with light elements. If a high energy particle spalls off some hydrogen atoms, then those can be less damaging than a similar collision in steel or lead. Fungi is a mixture of mostly light elements.

But that's about the extent of my knowledge.

Do you happen to know if in a composite shielding situation (several layers of multiple materials) would you put the lead on the outside facing the hard radiation, or on the inside?

The other advantage of fungi might be in the aftermath of a micrometeoroid event. Does it make more sense to cut a hole in your shielding and use up a store of fungal bricks that you brought with you, or to grow a somewhat custom patch with the right radius of curvature, and slightly larger than the hole, and then recycling any material that gets removed to apply the patch.

If the shield is actually alive (say, a layer around your emergency shelter), then you can just fill the hole with food and let the fungi patch themselves, and any damage caused by being exposed to partial vaccuum. Possibly with a mold that also acts as a temporary, reusable patch over the worst hit areas, so that a subsequent space storm doesn't catch you with your pants down.

Surely you’d need a lot more water than lead?

At least you can be using the water though.

The water will accumulate deuterium and tritium over time though. Eventually, it will degrade to emergency drink status. Might be a good way to get at fusion reactor fuel though.

Will it also accumulate heavy oxygen?

There is a few radioactive isotopes of oxygen that I think could be produced by gamma bombardment, O-15, and a few others. They decay very quickly to nitrogen though. Over time, this could turn into an interesting mix of elements.

Maybe we should think of the fungus as self-managing water storage and plumbing.

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