3 ms·

As mentioned in another comment, water is a radiation shield, but ionizing radiation in space will attenuate 50% after 7cm of water (I could be wrong), and if y

As mentioned in another comment, water is a radiation shield, but ionizing radiation in space will attenuate 50% after 7cm of water (I could be wrong), and if you want a lot of attenuation, you need a lot of water (which is extremely heavy). A small amount of water for shielding is undoubtedly much more massive than simply using bigger, rad-hard processors.

gpm 6y ago
I don't see any comments about water on this post? If we're talking about $50/kg [1] in the future... well... - Sending a few kg of water (or other shielding) to space costs a fraction of the price of a fast non-rad-hardened CPU. - It really costs less than the extra development cost associated with having to use bespoke toolchains. [1] Number from the other space post on the front page today: https://getmeflyingcars.medium.com/how-much-does-it-cost-to-send-1kg-to-lower-earth-orbit-2852e1821a6d https://getmeflyingcars.medium.com/how-much-does-it-cost-to-...
- klodolph 6y ago
  > I don't see any comments about water on this post? Looks like it was deleted. > - Sending a few kg of water (or other shielding) to space costs a fraction of the price of a fast non-rad-hardened CPU. It doesn’t sound like a few kg is going to cut it. Recall that a 1 kg of water is about 1 L, which gives you about 6 cm of shielding, which is simply not enough. That’s less than 50% attenuation of the ionizing radiation you find in space. Mass increases with the cube of the thickness. If you want 20 cm of shielding, that’s 33 kg, and something like 86% attenuation. It seems to me like there are better things you can do with your mass, which also needs to be spent on things like fuel for stationkeeping. Lower mass also means more satellites. > - It really costs less than the extra development cost associated with having to use bespoke toolchains. POWER is not exactly some obscure ISA. It is well-supported and battle-tested. You don’t need a bespoke toolchain.
  - p_l 6y ago
    The most bespoke parts would be tool chain certification, which among other things, covers "if I have source A, then I can be sure resulting machine code does B, not anything else". And that's something you'll get even if you're running MS-DOS on 286 in space ;-)

gpm 6y ago

I don't see any comments about water on this post? If we're talking about $50/kg [1] in the future... well... - Sending a few kg of water (or other shielding) to space costs a fraction of the price of a fast non-rad-hardened CPU. - It really costs less than the extra development cost associated with having to use bespoke toolchains. [1] Number from the other space post on the front page today: https://getmeflyingcars.medium.com/how-much-does-it-cost-to-send-1kg-to-lower-earth-orbit-2852e1821a6d https://getmeflyingcars.medium.com/how-much-does-it-cost-to-...

klodolph 6y ago
> I don't see any comments about water on this post? Looks like it was deleted. > - Sending a few kg of water (or other shielding) to space costs a fraction of the price of a fast non-rad-hardened CPU. It doesn’t sound like a few kg is going to cut it. Recall that a 1 kg of water is about 1 L, which gives you about 6 cm of shielding, which is simply not enough. That’s less than 50% attenuation of the ionizing radiation you find in space. Mass increases with the cube of the thickness. If you want 20 cm of shielding, that’s 33 kg, and something like 86% attenuation. It seems to me like there are better things you can do with your mass, which also needs to be spent on things like fuel for stationkeeping. Lower mass also means more satellites. > - It really costs less than the extra development cost associated with having to use bespoke toolchains. POWER is not exactly some obscure ISA. It is well-supported and battle-tested. You don’t need a bespoke toolchain.
- p_l 6y ago
  The most bespoke parts would be tool chain certification, which among other things, covers "if I have source A, then I can be sure resulting machine code does B, not anything else". And that's something you'll get even if you're running MS-DOS on 286 in space ;-)