3 ms·

In a sense, it may have been a good thing we didn't attempt a manned Venus fly-by in the 70s. Even today, we aren't sure we can sufficiently shield spacecraft f

by mabbo 9y ago

In a sense, it may have been a good thing we didn't attempt a manned Venus fly-by in the 70s. Even today, we aren't sure we can sufficiently shield spacecraft from radiation outside of the earth's magnetosphere. Imagine the public perception of NASA had every astronaut that went to Venus come home and slowly died of multiple cancers.

Robotbeat 9y ago
Meh, radiation concern is over-rated. Astronauts and cosmonauts have spent more than a year in orbit, and the longest cumulative time in space (for one person) is over 800 days. YES, this is LEO, where the radiation levels are lower, but the levels of radiation aren't actually that much higher once you minus out the relatively-easily-shielded solar particle radiation. It's about a factor of 2 higher in deep space vs LEO. So as far as cumulative dose, we've already achieved that without "slowly dying of multiple cancers." And really, it takes a lot more cumulative dose than that to have a large and statistically meaningful cancer risk increase. We're talking about a 3% risk of cancer death, not 90% as you're implying (and the risk is relatively linear). The nice thing about Venus flyby is that provided you can shield the solar radiation (using water and supplies), the interplanetary magnetic field is stronger the closer to the Sun you get, so the very difficult-to-shield cosmic ray dose actually reduces. And another note about deep space radiation: there's an incorrect assumption out there that you do not receive the highest energy cosmic ray radiation in LEO due to the Earth's magnetic field. That's not true. The Earth's magnetic field can only shield the lower energy cosmic rays (the ones that are easier to shield using supplies and spacecraft mass). The highest energy cosmic rays, above the "geomagnetic cutoff," still get through, and they're the hardest to shield and also the ones that people say the effects are least known. However, we've had dozens of astronauts & cosmonauts spend ~6 month stints in space with exposure to these rays without any dramatic effects (and some have spent a year or more at a time). I'd venture that a crewed Venus flyby ("ma'ammed" as well as manned, since this is Venus afterall!!!) in the 1970s was perfectly doable from this perspective, given enough supplies and basic shielding from solar particle events. It would've been risky, but perhaps no more risky than Apollo 11, which had to actually land on and launch from a rocky body (a huge extra source of risk). Skylab had a >80 day mission in the 1970s, and the Soviets did a >175 day mission in 1979. I think a Venus flyby in the 70s would've been feasible.
- mabbo 9y ago
  These are really good points. Maybe the risks are over-stated. I guess as we (finally) start getting out there, going to Mars, etc, we're going to find out for sure.
- scrumper 9y ago
  Isn't the problem more those occasional solar flares than steady-state cosmic radiation? All longterm spaceflight so far has been inside the van Allen belts which offer quite a bit of protection (for us on earth too).
  - Robotbeat 9y ago
    The solar flares' radiation is relatively easy to shield against. You can arrange your food and water supplies to provide temporary shielding. Even a very small amount of shielding (like simply being inside a spacecraft) will stop the worst effects. Here's a graph showing some really bad solar flares and how aluminum (which is a terrible shielding material compared to food and water) reduces the dose: http://www.bioedonline.org/slides/content-slides/space-life-sciences/radiation-effects/?pageaction=displaySlideDetails&tk=56&dpg=13 http://www.bioedonline.org/slides/content-slides/space-life-...
    - scrumper 9y ago
      OK interesting, thanks for sharing. Shielding in general does seem to be a real issue for any spaceflight beyond LEO though; perhaps not as bad as I'd thought.

by mabbo 9y ago

Robotbeat 9y ago

Meh, radiation concern is over-rated. Astronauts and cosmonauts have spent more than a year in orbit, and the longest cumulative time in space (for one person) is over 800 days. YES, this is LEO, where the radiation levels are lower, but the levels of radiation aren't actually that much higher once you minus out the relatively-easily-shielded solar particle radiation. It's about a factor of 2 higher in deep space vs LEO. So as far as cumulative dose, we've already achieved that without "slowly dying of multiple cancers." And really, it takes a lot more cumulative dose than that to have a large and statistically meaningful cancer risk increase. We're talking about a 3% risk of cancer death, not 90% as you're implying (and the risk is relatively linear). The nice thing about Venus flyby is that provided you can shield the solar radiation (using water and supplies), the interplanetary magnetic field is stronger the closer to the Sun you get, so the very difficult-to-shield cosmic ray dose actually reduces. And another note about deep space radiation: there's an incorrect assumption out there that you do not receive the highest energy cosmic ray radiation in LEO due to the Earth's magnetic field. That's not true. The Earth's magnetic field can only shield the lower energy cosmic rays (the ones that are easier to shield using supplies and spacecraft mass). The highest energy cosmic rays, above the "geomagnetic cutoff," still get through, and they're the hardest to shield and also the ones that people say the effects are least known. However, we've had dozens of astronauts & cosmonauts spend ~6 month stints in space with exposure to these rays without any dramatic effects (and some have spent a year or more at a time). I'd venture that a crewed Venus flyby ("ma'ammed" as well as manned, since this is Venus afterall!!!) in the 1970s was perfectly doable from this perspective, given enough supplies and basic shielding from solar particle events. It would've been risky, but perhaps no more risky than Apollo 11, which had to actually land on and launch from a rocky body (a huge extra source of risk). Skylab had a >80 day mission in the 1970s, and the Soviets did a >175 day mission in 1979. I think a Venus flyby in the 70s would've been feasible.

mabbo 9y ago
These are really good points. Maybe the risks are over-stated. I guess as we (finally) start getting out there, going to Mars, etc, we're going to find out for sure.
scrumper 9y ago
Isn't the problem more those occasional solar flares than steady-state cosmic radiation? All longterm spaceflight so far has been inside the van Allen belts which offer quite a bit of protection (for us on earth too).
- Robotbeat 9y ago
  The solar flares' radiation is relatively easy to shield against. You can arrange your food and water supplies to provide temporary shielding. Even a very small amount of shielding (like simply being inside a spacecraft) will stop the worst effects. Here's a graph showing some really bad solar flares and how aluminum (which is a terrible shielding material compared to food and water) reduces the dose: http://www.bioedonline.org/slides/content-slides/space-life-sciences/radiation-effects/?pageaction=displaySlideDetails&tk=56&dpg=13 http://www.bioedonline.org/slides/content-slides/space-life-...
  - scrumper 9y ago
    OK interesting, thanks for sharing. Shielding in general does seem to be a real issue for any spaceflight beyond LEO though; perhaps not as bad as I'd thought.