That headline title.
But then again, why is this needed? Won't they be getting plenty of radiation soon as they're outside the o-zone layer? Does our normal method of radiation shielding decay over time, or something?
(Total layman here, curious)
But then again, why is this needed? Won't they be getting plenty of radiation soon as they're outside the o-zone layer? Does our normal method of radiation shielding decay over time, or something?
(Total layman here, curious)
The water and food, and "the stuff water and food turns into over the course of a trip" as the joke goes, are very useful as a "storm shelter" against a solar flare. If one comes up and the crew is not shielded like this against the solar flare, they will die within a day or two.
Cosmic rays are very hard to effectively shield against. They don't stop for much, including people, but there are so many of them that you are bound to take a dose. Right now the best way to deal with it, for temporary trips in space, is probably just to deal with it: accept the 1% or 2% rise in cancer risk, and make up for it with superior health care once they are back on Earth.
Honestly I had no idea it was so active up there.
Solar flare particles are very eager to find something to interact with. But flip side of that it only takes a few inches (IIRC) of water, or a watery substance, to absorb them.
Cosmic rays, on the other hand, are likely to pass right through the entire spacecraft without interacting with anything. The problem is that there are so many of them that, by chance, some will decide to stop inside your body and dance on your DNA. It takes something like a planet to really completely block them.
I don't know where you get the idea that it takes an entire planet to protect you from solar flares or cosmic rays, that's very wrong, solar flares are not that penetrating. In fact, on Earth almost all particle radiation from solar flares (and from cosmic rays) is stopped by the upper atmosphere.
Edit: added additional clarification.
Just wanted to point out he was talking about cosmic rays with the planet comment. And added the ;) to try and not be a dick about it. Not sure how that worked out.
I brought up a planet only for the fact that you would need something really really big to block all cosmic rays. I did not mean to imply it was necessary. People on Earth are hit from cosmic rays from "above" as part of our background radiation.
Also, to be precise people aren't hit by primary cosmic rays on Earth but by secondary cosmic rays, the particle debris from high energy protons and nuclei colliding with atoms in the upper atmosphere.
Over a long term interplanetary voyage, the chances of cancers developing would probably approach 100%.
I think the idea is, you're going to have to carry all that water to Mars anyway, and it just happens to be the best form of shielding around.
You could make your shielding dual-purpose. Material that serves another purpose could be put around the outside of the spacecraft and act as shielding.
Machinery doesn't work too well, because it needs to be in a particular spot to work, and there isn't enough of it, and the stuff it's made out of isn't the best material for shielding.
Food and water, on the other hand, you can store just about anywhere. It's pretty good shielding too. For a Mars trip, you need a lot of it.
However, it's consumable. Food might be good shielding at the start of the trip, but there won't be much left at the end. Fortunately, food doesn't disappear when eaten, it's just transformed. The transformed food is still just about as good at shielding as the original was.
I assume this is more or less the chain of thought that got to this point.
All of our manned spaceflights except for Apollo have been in low Earth orbit. Nestled deep down inside of Earth's magnetosphere protects you from a lot of radiation. Being above the ozone layer means that you are exposed to more ultraviolet light, but this isn't a big deal because it's not like you "go outside" much, you'll always have a window or a helmet between you and the Sun and those will always have a UV filter. The real issue is particle radiation, which comes from the Sun, the galaxy, and from parts of Earth's magnetosphere (the van allen belts). In low Earth orbit a lot of the solar and cosmic particle radiation is blocked, and as long as you steer clear of the van allen belts at high altitudes you'll be alright. The aluminum skin of spacecraft will protect you from some radiation, and you can add additional mass, especially water, to add more radiation protection. Overall in Earth orbit the radiation environment is fairly mild though a bit on the concerning side if you were to live there for decades.
If you have to travel through the van allen belts or outside Earth's protective magnetospheric bubble then things get much more difficult. In the case of the Apollo program they were careful to ensure that the thickness of the spacecraft's skin was enough to block a goodly amount of particle radiation and they designed the mission profile such that the spacecraft passed through the van allen belts as quickly as possible (spending as little time exposed to their radiation as could be managed). And in terms of operations in orbit around or on the Moon the main advantages was again one of time. Astronauts only spent at most a few days up there, limiting their radiation doses. However, they were extremely vulnerable to solar flares, which could have subjected them to extremely high doses of radiation that they had no way to protect against. In that they just got lucky.
A Mars mission, however, will spend months in interplanetary space and the chance of the crew being subjected to the radiation from a solar flare are very much higher. Additionally, they'll be subjected to much higher accumulated doses of radiation just by being in interplanetary space for so long. The thin aluminum skin of a spacecraft won't be sufficient protection for these conditions, so they'll need both a greater level of day to day protection and also an area of heavy protection that they can use to ride out solar flares and CMEs. Generally large masses of water or organic material work the best in protecting from the high energy protons that are the most concerning source of radiation in interplanetary space.
P.S. There's another option for shielding which is to generate a miniature magnetosphere around a spacecraft. This has a lot of advantages but the biggest disadvantage is that it would require additional equipment (weight is the biggest constraint on any Mars mission) as well as a significant amount of power and the technology hasn't been proven yet. Here's a neat paper on the subject: http://www.ess.washington.edu/Space/M2P2/rad.shielding.pdf
The other complication for an m2 radiation shield is that it would be slightly propulsive, which would slightly complicate planning trajectory planning (though not badly so).