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Comment by albertzeyer | Hacker News Reader

Where do you have that 52,000 millirem (i.e. 520 mSv) number from?

Doesn't that completely depend on the thickness and material of the walls of the spacecraft? I.e., isn't it just a question of making the walls thick enough?

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I occasionally get to work with the Astronomical Society and have gotten into a few conversations about manned Mars missions with people from NASA, JPL and various educational institutions. The numbers are from a study NASA conducted at Brookhaven National Laboratory.

The problem with shielding is the weight involved to achieve any level of protection.. wrapping the ship in enough lead to make a difference would be hard to get it off the ground. Also while this type of shielding may be effective against normal solar radiation, high energy galactic cosmic rays are far more dangerous and are almost unaffected by conventional shielding.

If you're interested, I recommend this paper. It goes a bit deeper into exactly why radiation is such a problem for any proposed Mars missions (warning, PDF):

http://spaceradiation.usra.edu/references/Ch4RadCarcinogen.p...

Why does the entire spacecraft have to go up at once? Also, why does the entire spacecraft have to go down?

Ya, you should swing by the space station and pick up your lead shielding on the way out, drop it back off on the way home.

Iss is in the wrong orbit for that.

Something could be put in the right orbit for it?

Couldn't the shielding be left with the ISS?

Good point, and would that would take care of the gravity well aspect of the issue. You'd still have the same amount of mass to accelerate, though. I suppose that wouldn't be as much of an issue once you weren't fighting Earth's gravity as well as inertia.

It doesn't. However, the more launches required to assemble your spacecraft, the more chances there are for something to go wrong.

That's a silly argument. You could just as well say that the more things you launch that aren't a passenger-loaded vehicle, the more likely you'll have worked out the glitches by the time large numbers of lives depend on it.

A mission to Mars is guaranteed to be the most complex space mission ever attempted. Every additional rocket you need for the mission adds complexity. Complexity is the enemy of reliability.

What happens to your Mars departure window when the rocket carrying your life support system goes off course and is destroyed by the range safety officer?

This is a pretty relevant and interesting read about magnetic shielding.

http://www.thespacereview.com/article/308/1

I hope this technology is thoroughly investigated before moving forward with the standard absorption method of radiation protection.

Unless I'm missing something interesting (maybe a plasma shield?), this only works for radiation with an electric charge - protons, electrons, helium nuceli. Cosmic rays and other EM radiation are not affected by a magnetic field.

Cosmic rays are energetic charged subatomic particles, originating in outer space; i.e. they will be affected by magnetic field. About 89% of cosmic rays are simple protons or hydrogen nuclei, 10% are helium nuclei or alpha particles, and 1% are the nuclei of heavier elements. The term ray is historical as cosmic rays were thought to be electromagnetic radiation. [Quoted from Wikipedia]

I didn't read the whole paper, but your own link completely disagrees with your 52,000mrem/520sV-figure:

    Whole body doses of 1 to 2 mSv/day accumulate in interplanetary space, and 
    approximately half of this value accumulates on planetary surfaces (Cucinotta et 
    al., 2006; NCRP, 2006).

That's millisieverts per day, not sieverts. Am I missing something?

52,000 millirem is 520 mSv, not 520Sv. This number is taken from the Brookhaven National Lab tests. The paper may be talking there about accumulated absorbed radiation, not total exposure.

That's what I was thinking. Not to mention, I would imagine that anti-radiation technology has surely grown in capability since the Apollo missions.

Practically it really hasn't. Polyethylene is being tested in NASA's Radiation Shielding Program but I don't believe it's been put into service for a manned mission. There are also tests being conducted with adjustable "magnetic bubbles" that can in theory shield a spacecraft from radiation, but the last I heard they were done on a much smaller scale and would require a huge amount of power.

NASA has been making progress in making astronauts less susceptible to radiation damage through diet and vitamins. There's also this paper which talks about a vaccine that's being tested to counteract some of the body's responses to radiation exposure (PDF):

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2007002...

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