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Why not place a solenoid at the apex or highest elevation point of surface habitation units e.g. apex of dome or other shaped structure to help protect the inhabitants from cosmic and solar radiation coming from the sky? The solenoid could be switched on or off as required and would be sufficient to stop or greatly reduce any remaining radiation getting through the Martian atmosphere.
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Ah the creation of a magnetic field or RF field depending on the source of power sent into the coil with or without any ferrite materials for a core that these windings are place around. Some of this was covered in this topic...
Artificial Magnetosphere - Electromagnetic Induction
Static shield concepts are part of a lunar colony...
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As far as I know, charged particles aren't a worry on Mars, since the atmosphere is thick enough to block it. It's the steady flux of cosmic radiation that's the issue, and that can't be practically blocked with anything other than sheer mass.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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Cosmic rays are an issue on Mars. They hit the upper atmosphere producing a shower of secondary particles, much as they do on Earth. The Martian atmosphere has only 1.6% of the column density of Earth's atmosphere, so most of those particles reach the ground. On the plus side, they individually have less energy than the original cosmic ray. So the magnetic field need not be as strong as it would need to be in free space.
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As far as I know, charged particles aren't a worry on Mars, since the atmosphere is thick enough to block it. It's the steady flux of cosmic radiation that's the issue, and that can't be practically blocked with anything other than sheer mass.
Actually, the report from the MARIE team, the radiation instrument on Mars Odyssey, found the reverse. Mars atmosphere blocks 90% of heavy ion galactic cosmic radiation at a high altitude location like Meridiani Planum where Opportunity landed. Or 98% at a low altitude location such as Elysium Planetia where Spirit landed. Curiosity landed in a river delta, but Spirit landed on the dried-up ocean basin. However, the lighter the particle, the less effective atmosphere is. So it's less effective blocking medium ion GCR, most light ion GCR gets through, and almost all proton radiation from the Sun reaches the surface.
There's very little GCR, and it's steady. Solar radiation is the issue. Most of the time it's fine, about half that of ISS. At a low altitude location like Curiosity or Spirit, radiation is less than half of ISS. The issue is a solar flair or Coronal Mass Ejection (CME). That's highly intense radiation for a short time. It's from the Sun, so mostly proton radiation, and low energy compared to GCR.
Beta radiation is high speed free electrons. It's so low mass that human skin can stop it. Or a single sheet of paper, or single layer of plastic film. Alpha radiation is a helium nuclei; it's stopped by a single layer of aluminum foil. Aluminized Mylar of multi-layer insulation of a spacesuit will stop it. Or spectrally selective coating on a polymer film greenhouse. Space doesn't have much X-rays, the metal of spectrally selective coating should be enough to block that. The coating is specifically designed to block UV-C, UV-B, and most of UV-A.
That just leaves proton, gamma, and light ion GCR. Regolith effectively blocks that.
A magnetic field strong enough and high enough *MIGHT* deflect solar proton radiation.
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Do we really have to worry about particle radiation from the Sun? I'm sure everyone here has read this paper on Curiosity's radiation measurements on Mars, it details the one solar energetic particle event Curiosity had witnessed at the time of the study. The dose equivalent for that event was only 0.025 mSv, a small fraction of the dose equivalent rate from GCRs for a normal day on the surface of Mars.
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Yes, you DO have to worry about solar flare radiation. It DOES NOT follow a trend, the way GCR does. There's nothing, then erratically, there's a lethally intense burst a few to several hours long.
These are unpredictable events on the sun, a bit more frequent during sunspot max activity than during sunspot min, but they can and do occur throughout the cycle. Erratically. Nothing, then death. The erratic behavior is compounded by direction: these are very directional events, not spread throughout space.
In 1972 there was one between two Apollo missions to the moon. Had we had a crew out there, they would have died within hours. It's a dose like that obtained during the first hours of fallout after a surface atomic blast.
It's far lower energy-per-particle than GCR, so thin shielding (about 15-20 cm water equivalent) really is feasible. But there's so much more of it when it does occur, that it is entirely and quickly lethal without that shielding.
High-dose radiation poisoning is a really ugly death, and it cannot be reversed. We've already seen it in the two Japanese cities and in nuclear accidents.
The longer one is out there, the more likely one of these will occur, but you cannot say when, very much like the California earthquake risks. We "got away" with taking the risks unprotected during Apollo, because those missions never exceeded 2 weeks duration. Mars is 6-8 months 1-way, 13 months there, and 6-8 months home. These things occur crudely every few months to a few years. The odds are pretty good a crew will get hit somewhere during the trip. And Mars has no magnetic field to shield the crew on the surface.
GW
Last edited by GW Johnson (2017-09-23 13:04:54)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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GW, I agree that we do have to worry about solar particle emissions in space. But this topic is about radiation protection on the surface of Mars, where there already is some thin shielding.
Mars' atmosphere is about 600 Pa, so the weight of Mars' atmosphere is about 600 N/m^2. That means that the mass per area of Mars' atmosphere is 600/3.7=162 kg/m^2, or 16.2 g/cm^2. This is very close to the level of shielding you suggest for protecting against solar energetic particles.
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I agree that Mars's thin atmosphere provides some shielding effect. I'm not sure it's enough for a big X-class flare in a direct hit on the sunward side.
Here, the magnetic field deflects direct impact, plus we have a very much thicker atmosphere. That's why we only see radio/TV disruptions and sometimes electrical blackouts. The downside is those particles accumulate in lethal belts we call the Van Allen belts. Crews must traverse that region quickly to limit dose. We did that quite easily in Apollo.
Radiation levels in space during bad solar flare events fall somewhere around 10^3 to over 10^4 REM/hour. Yep, per hour! These events are a few to several hours long, so you can see the problem, when 500-1000 REM accumulated in a "short interval" is considered to be a uniformly-fatal dose.
If the shielding effect of Mars's atmosphere is around half an order of magnitude to an order of magnitude as a reduction factor, then that's just not enough. The crew just needs a safe place to hide for a few hours. Some tin-can / tuna-can habitat or plastic-balloon greenhouse ain't it. A few sand bags wet-down and allowed to freeze, then piled onto the roof, would be.
I personally like 20 cm of water equivalent better than I do 15 cm. More is just better. I don't think we yet understand just how large an X-class flare event really can be.
GW
Last edited by GW Johnson (2017-09-23 15:31:20)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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During the Mars Homestead project, one member was a master student in nuclear engineering at MIT. Another individual was a master student in nuclear physics at MIT. They calculated regolith over the habitat of 2.4 metres deep (8 feet) should reduce radiation exposure to equal annual exposure to a radiation worker in the US. Our design was built into a hillside. The edge would have regolith 2.4 metres deep. I suggested an "awning" over each apartment window, providing shade. This awning would be made of reinforced concrete with a lip holding regolith. The concrete plus regolith would equal 2.4 metres depth or greater, and configured so it provides shade. The reason for shade is radiation protection. East facing windows would have direct sunlight a number of minutes during sunrise, west facing windows during sunset. But the settlement we designed had south facing windows, not east or west, so no direct sunlight through apartment (bedroom) windows. Furthermore, since it was built into a hillside, common spaces were deeper into the hill, which meant deeper regolith overhead. During a major CME, settlers would move away from spaces near the hill edge (apartments, rover garage, workshop) and definitely out of the greenhouses. They would wait out the CME in the atrium, with much deeper regolith overhead. And seed bank storage would be in a room even deeper into the hillside.
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I think I underestimated how big a solar flare can be. The largest we've measured was an X-28 in 2003, 43 times the flux of the M-6.5 flare that caused the SEP event that Curiosity measured. If the relationship between flare flux and radiation reaching Mars' surface was linear, that would still mean only 1 mSv for an X-28 flare. But the relationship could be very different, which makes the danger of SEP events uncertain. You've convinced me that this is a potential problem.
I think the biggest question is "do high energy SEP events have significantly higher energies per particle?". Reading through the paper I linked before again, I noticed the authors say that Mars' atmosphere blocks particles with energies of less than 150 MeV. So almost all of the energy from the flare Curiosity measured was blocked by the atmosphere. But if larger events also have a much larger proportion of particles above 150 MeV (which is practically in the range of cosmic rays), then that could pose serious danger to astronauts on Mars' surface. Have we taken any radiation measurements on Mars during larger SEP events?
One final note, shielding in gale crater is actually 20 g/cm^2, slightly higher than the average because of its low altitude. So if we visit low altitudes on Mars, we'll have a bit more protection than we otherwise would.
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I just came across this recent paper that models the radiation dose on Mars from solar particle events. Their conclusion is that even the Carrington Event would result in a mild surface radiation dose equivalent of under 20 mSv (see Fig. 10 on page 23). It looks like we can ignore solar particle radiation on Mars.
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A solenoid has low external B magnitude along its length, whereas a straight wire has maximum B magnitude. For surface facilities, straight-wire shielding geometries are desirable.
For a first concrete example of a Mars facility field, see our initial design for the "Omaha Field," one component of the "Omaha Shield" proposal:
Omaha Shield: radiation protection systems for Unlimited Mars Career
Last edited by Lake Matthew Team - Cole (2017-12-01 15:40:59)
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