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DaveMcW t1_iuibl9m wrote

Reply to comment by Wentoutonalimb in All Space Questions thread for week of October 30, 2022 by AutoModerator

The most dangerous radiation comes from outside the solar system and is called "galactic cosmic radiation". GCR is ionized hydrogen and helium atoms that are traveling very fast. It will destroy any DNA it hits, which is bad for humans.

There are four levels of GCR:

  • On the ground. 100km of air gives very good protection. GCR is not a significant health threat.
  • In low earth orbit. The earth's magnetic field gives some protection. We have measured increased cancer risk and cell damage from GCR in astronauts on the International Space Station.
  • In the solar system. GCR is a significant threat to people traveling to other planets. Our current calculations are that most people will survive the trip, but some will get cancer and die.
  • Outside the solar system. GCR is 10x higher outside the solar system. When you combine this with long travel times, an unshielded spaceship is a death trap. An interstellar spaceship would need a lot of radiation shielding.
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Wentoutonalimb t1_iuif1d3 wrote

Thank you so much for your comprehensive answer. Do you think this issue would make interstellar travel all but impossible? Is shielding from radiation typically lead in composition (like the lead aprons they give you for medical X-rays), or are there other kinds or technologies? I would imagine that lifting lead into space for this purpose would be prohibitively expensive.

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stalagtits t1_iuiindj wrote

> Do you think this issue would make interstellar travel all but impossible?

No, I don't believe so. The major hurdle to be solved is developing much, much more efficient engines. Radiation shielding has pretty good solutions already.

> Is shielding from radiation typically lead in composition (like the lead aprons they give you for medical X-rays), or are there other kinds or technologies?

The best material depends on the kind of radiation. For X-rays and the like (relatively low energy), lead works great. For galactic cosmic rays containing lots of proton and neutrons, things with a high hydrogen content (like polyethylene plastic) can work better and weigh less.

Water is also an excellent choice: It's decent at radiation protection and the ship will need a lot of it anyway (for drinking, cooling, growing food, possibly for the engines). Lining the outer hull with a layer of water could work. Or the ship could have a radiation vault encased in a thicker layer of water for the crew to take shelter in.

> I would imagine that lifting lead into space for this purpose would be prohibitively expensive.

The whole ship would be much, much heavier than the lining alone. If it is too expensive to launch the ship, dropping a bit of shielding mass won't make much of a difference. Without a breakthrough in the launch cost to Earth orbit, even regular interplanetary travel remains a pipe dream. SpaceX's Starship program aims to change that in the near future.

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grambell789 t1_iujno5w wrote

>>Radiation shielding has pretty good solutions already.

How much time could someone spend unshielded without significant effects? Like time spent space walking to fix something .

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