3 ms·

The Martian atmosphere may not but the surface of the planet does, cutting half the yearly dose versus being in deep space. And I'm not sure I buy the argument

The Martian atmosphere may not but the surface of the planet does, cutting half the yearly dose versus being in deep space. And I'm not sure I buy the argument that the atmosphere provides little protection. There's a lot of atmosphere there still, enough you can push down on it and rise into the sky if you have some carbon fiber blades moving at very high speeds. I'd think a iron nuclei would hit a lot of atoms on the way down. > you'll still get all the cancer sooner than later. Cancer risk from radiation is probabilistic. If you spend all day outdoors then you increase your lifetime risk of cancer by a significant degree, but it's not like you're definitely going to get cancer. Additionally, most habitation modules, at least early on, are planned to be buried in martian regolith. Also the moon is worse than Mars in all respects with regard to this so you're effectively arguing that humans should never leave the orbit of Earth. I'm not a fan of that future. (BTW, we deal with much higher radiation levels in hot cells in reactors here on Earth, and those even have windows into them. I'm sure we can work out something.)

idlewords 4y ago
You don't have to buy the argument; you can look up the scientific papers. Heavy ion radiation is hard to shield against and creates high energy secondary radiation when it hits air, metal, or rock. Moreover, there is strong evidence cancer risk from heavy ions is considerably greater than predicted by the absorbed dose model we use for other kinds of ionizing radiation. Search on "non targeted effects heavy ions" to read up on this; it's a fascinating topic. The upper error bar right now for a 1000 day Mars mission is upwards of 20% risk of radiation-induced death; most of this is from the heavy ion component of cosmic rays.
- mlindner 4y ago
  Rather than speculation it'd be useful if there was more hard science on the subject, you know by actually doing long term experiments on life in space being exposed to these heavy ions. You can find scientific papers on a lot of subjects where it's hard to get at objective fact arguing one way or another and it's hard to tell how factual they really are. Also why would you quote the "upper error bar"? I'd like to know the size of that error bar and what the median is. > The upper error bar right now for a 1000 day Mars mission is upwards of 20% risk of radiation-induced death; most of this is from the heavy ion component of cosmic rays. This is just an argument that you need to bury things in regolith, at least early on, until we get better shielding designed for heavy ions.
  - idlewords 4y ago
    Here's the specific citation: Assuming 940 day mission, percent risk of radiation-induced death for a 40 year old woman is: * mean: 8.8; 95% confidence [2.78, 21.0] For a 40 year old man: * mean: 6.49; 95% confidence [2.58, 13.6] Source is "Cancer and circulatory disease risks for a human mission to Mars: Private mission considerations", Acta Astronautica, 2018. Narrowing this uncertainty range requires long-duration human or animal experiments outside the magnetosphere.
    - mlindner 4y ago
      Thanks for the raw data. That's a very wide range.
    - Retric 4y ago
      It’s also dependent on the effectiveness of various cancer treatments as well as the specific location etc.
      - idlewords 4y ago
        These figures aren't limited to cancer, they include the risk of (also poorly understood) heavy ion radiation induced cardiovascular disease.
- Andrex 4y ago
  I'm not very knowledgeable, but couldn't we wrap the space suits in tinfoil or something?
  - idlewords 4y ago
    This works for lower energy particles (like protons from the sun), but for heavy ions partial shielding makes the problem worse than not having shielding at all, the small number that hit the metal instead of passing through create a shower of damaging secondary radiation. Effectively shielding people from cosmic rays requires either a thick atmosphere, a couple meters of soil, or really thick slabs of metal. The best solution on Mars might be to build a shelter inside a cave or lava tube, but then you run up afoul of international treaty obligations to not contaminate these sensitive environments. The short answer to your question is "yes, but the foil has to be three feet thick."
    - Retric 4y ago
      I mostly agree with that but you don’t need to hand wave as much. The atmosphere of mars is roughly equivalent too 2 inches of soil if the source is directly overhead and 3 inches at a 45 degree angle, but far more than that at low angles. Anything below the horizon is blocked by the surface of Mars, so you end up with well over 50% shielding from cosmic rays vs the trip to Mars. Being further from the sun is also beneficial. You definitely want to live and work underground on Mars or at minimum below a large water tank, but even just landing in a valley can noticeably reduce radiation exposure as the mountains block portions of the sky so too do they block a portion of cosmic rays.
      - idlewords 4y ago
        I think you have this backwards; GCR flux increases with distance from the sun.
        Retric 4y ago
        For GCR, but not total radiation exposure. Cosmic rays are a combination of solar energetic particles and GCR. Though this is dependent on how active the sun is: “If the instrument had been taking measurements on Mars during the comparable period of the solar-activity cycle about 11 years ago, it would probably have seen eight events in 300 sols, contributing an unknown but certainly significantly higher amount to the overall dose.” And of course if Mars was closer to the sun these numbers would be significantly higher. https://www.nasa.gov/jpl/msl/mars-rover-curiosity-pia17600.html https://www.nasa.gov/jpl/msl/mars-rover-curiosity-pia17600.h...

idlewords 4y ago

You don't have to buy the argument; you can look up the scientific papers. Heavy ion radiation is hard to shield against and creates high energy secondary radiation when it hits air, metal, or rock. Moreover, there is strong evidence cancer risk from heavy ions is considerably greater than predicted by the absorbed dose model we use for other kinds of ionizing radiation. Search on "non targeted effects heavy ions" to read up on this; it's a fascinating topic. The upper error bar right now for a 1000 day Mars mission is upwards of 20% risk of radiation-induced death; most of this is from the heavy ion component of cosmic rays.

mlindner 4y ago
Rather than speculation it'd be useful if there was more hard science on the subject, you know by actually doing long term experiments on life in space being exposed to these heavy ions. You can find scientific papers on a lot of subjects where it's hard to get at objective fact arguing one way or another and it's hard to tell how factual they really are. Also why would you quote the "upper error bar"? I'd like to know the size of that error bar and what the median is. > The upper error bar right now for a 1000 day Mars mission is upwards of 20% risk of radiation-induced death; most of this is from the heavy ion component of cosmic rays. This is just an argument that you need to bury things in regolith, at least early on, until we get better shielding designed for heavy ions.
- idlewords 4y ago
  Here's the specific citation: Assuming 940 day mission, percent risk of radiation-induced death for a 40 year old woman is: * mean: 8.8; 95% confidence [2.78, 21.0] For a 40 year old man: * mean: 6.49; 95% confidence [2.58, 13.6] Source is "Cancer and circulatory disease risks for a human mission to Mars: Private mission considerations", Acta Astronautica, 2018. Narrowing this uncertainty range requires long-duration human or animal experiments outside the magnetosphere.
  - mlindner 4y ago
    Thanks for the raw data. That's a very wide range.
  - Retric 4y ago
    It’s also dependent on the effectiveness of various cancer treatments as well as the specific location etc.
    - idlewords 4y ago
      These figures aren't limited to cancer, they include the risk of (also poorly understood) heavy ion radiation induced cardiovascular disease.
Andrex 4y ago
I'm not very knowledgeable, but couldn't we wrap the space suits in tinfoil or something?
- idlewords 4y ago
  This works for lower energy particles (like protons from the sun), but for heavy ions partial shielding makes the problem worse than not having shielding at all, the small number that hit the metal instead of passing through create a shower of damaging secondary radiation. Effectively shielding people from cosmic rays requires either a thick atmosphere, a couple meters of soil, or really thick slabs of metal. The best solution on Mars might be to build a shelter inside a cave or lava tube, but then you run up afoul of international treaty obligations to not contaminate these sensitive environments. The short answer to your question is "yes, but the foil has to be three feet thick."
  - Retric 4y ago
    I mostly agree with that but you don’t need to hand wave as much. The atmosphere of mars is roughly equivalent too 2 inches of soil if the source is directly overhead and 3 inches at a 45 degree angle, but far more than that at low angles. Anything below the horizon is blocked by the surface of Mars, so you end up with well over 50% shielding from cosmic rays vs the trip to Mars. Being further from the sun is also beneficial. You definitely want to live and work underground on Mars or at minimum below a large water tank, but even just landing in a valley can noticeably reduce radiation exposure as the mountains block portions of the sky so too do they block a portion of cosmic rays.
    - idlewords 4y ago
      I think you have this backwards; GCR flux increases with distance from the sun.
      - Retric 4y ago
        For GCR, but not total radiation exposure. Cosmic rays are a combination of solar energetic particles and GCR. Though this is dependent on how active the sun is: “If the instrument had been taking measurements on Mars during the comparable period of the solar-activity cycle about 11 years ago, it would probably have seen eight events in 300 sols, contributing an unknown but certainly significantly higher amount to the overall dose.” And of course if Mars was closer to the sun these numbers would be significantly higher. https://www.nasa.gov/jpl/msl/mars-rover-curiosity-pia17600.html https://www.nasa.gov/jpl/msl/mars-rover-curiosity-pia17600.h...