Author Topic: Dear SpaceX: You're incorrect about solar flare radiation. (Constructive)  (Read 2550 times)

Offline Robotbeat

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Elon Musk has on multiple occasions suggested that shielding pointed to the Sun would block solar flare radiation. That's wrong for two reasons:

1) Solar flare radiation doesn't travel straight from the Sun, it travels along (spiraling along) the Sun's magnetic field (which is called the Interplanetary Magnetic Field--IMF), whose field lines actually spiral outward, not in straight lines but curved. At Earth, the field lines are curved such that the lines are usually around 45 degrees from the Sun's rays, and at Mars, even greater. See the attached image.

2) Solar flare radiation does not actually arrive from one single direction. Although the energetic particles do follow the IMF lines, they do so on spirals. They also can and do reflect /backward/. This means that the radiation comes in at all sorts of directions, not just from a single one. That means you can't just place your shielding toward the IMF lines and expect to be well-shielded. You really need to place shielding all around.

Now some caveats: The solar flare radiation is not quite /perfectly/ isotropic, so there may be something gained from finding out where the particles are most coming from. Also, the particles in a solar particle event can actually cause the IMF to change locally. It's difficult to predict beforehand exactly what WOULD be the /most/ optimum place to concentrate shielding provided there is significant anisotropy.

And it doesn't take much shielding to mitigate against solar flares. In fact, even the mass of the hull should be enough to prevent any immediately life-threatening doses (see attached) from even some of the worst recorded flares. But repositioning supplies can also provide a lot of extra shielding without requiring any extra mass. If all the crew huddled in the center of the ship surrounded fairly evenly by supplies, the dose should not only be low enough to prevent any life-threatening acute effects, but even things like nausea would be prevented from even the worst flares.

(source for bottom image: http://www.bioedonline.org/videos/lecture-series/symposium-for-space-life-science/radiation-effects/ )
« Last Edit: 11/04/2016 12:36 AM by Robotbeat »
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Offline meekGee

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Elon Musk has on multiple occasions suggested that shielding pointed to the Sun would block solar flare radiation. That's wrong for two reasons:

1) Solar flare radiation doesn't travel straight from the Sun, it travels along (spiraling along) the Sun's magnetic field (which is called the Interplanetary Magnetic Field--IMF), whose field lines actually spiral outward, not in straight lines but curved. At Earth, the field lines are curved such that the lines are usually around 45 degrees from the Sun's rays, and at Mars, even greater. See the attached image.

2) Solar flare radiation does not actually arrive from one single direction. Although the energetic particles do follow the IMF lines, they do so on spirals. They also can and do reflect /backward/. This means that the radiation comes in at all sorts of directions, not just from a single one. That means you can't just place your shielding toward the IMF lines and expect to be well-shielded. You really need to place shielding all around.

Now some caveats: The solar flare radiation is not quite /perfectly/ isotropic, so there may be something gained from finding out where the particles are most coming from. Also, the particles in a solar particle event can actually cause the IMF to change locally. It's difficult to predict beforehand exactly what WOULD be the /most/ optimum place to concentrate shielding provided there is significant anisotropy.

And it doesn't take much shielding to mitigate against solar flares. In fact, even the mass of the hull should be enough to prevent any immediately life-threatening doses (see attached) from even some of the worst recorded flares. But repositioning supplies can also provide a lot of extra shielding without requiring any extra mass. If all the crew huddled in the center of the ship surrounded fairly evenly by supplies, the dose should not only be low enough to prevent any life-threatening acute effects, but even things like nausea would be prevented from even the worst flares.

(source for bottom image: http://www.bioedonline.org/videos/lecture-series/symposium-for-space-life-science/radiation-effects/ )
Does it ever curve so bad that it has a radial component that is towards the sun?
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Offline Robotbeat

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A component? Sure. A component.
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Offline meekGee

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A component? Sure. A component.

So it's actually spiraling back towards the sun?

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Offline MikeAtkinson

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Now some caveats: The solar flare radiation is not quite /perfectly/ isotropic, so there may be something gained from finding out where the particles are most coming from. Also, the particles in a solar particle event can actually cause the IMF to change locally. It's difficult to predict beforehand exactly what WOULD be the /most/ optimum place to concentrate shielding provided there is significant anisotropy.

I have seen (nearly) isotropic radiation asserted several times, but have not seen a source.

Later: I've read several papers now and it seems the topic is not straightforward. There are bow shocks, periods of anisotropic and isotropic radiation, differing effects at different particle energies and at varying distances from the Sun. It seems CMEs are very variable and most of the papers seem to be about why the standard model does not apply to the event(s) being looked at (which are more interesting from a research point of view). I haven't found an overview analysis yet, which gives the typical behaviour and probabilities of variation from that.

Online guckyfan

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It sounds like the rocket is pointed engines to the sun during the flight and there is no reason to change it. Unless there is a number of radiation sensors pointing in all directions and during a solar event the engines are pointed in the direction of highest radiation, whatever that direction is.


Offline Robotbeat

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The more important reason to keep the engines pointed to the Sun is for thermal management. SPEs can last a ~day. Don't want your methane and oxygen boiling off while you vainly attempt to slightly reduce SPE radiation dose. Just hang out in the center of the ship surrounded by your rations and you'll be very well-shielded from SPEs.
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Online guckyfan

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The more important reason to keep the engines pointed to the Sun is for thermal management.

Sorry, that is what I meant. Should have been more clear.

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