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Old 05-17-2010, 04:52 AM   #1
Cairan
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Post Manned exploration of Jupiter and Radiation hazard

Here's a quick analysis for planning and realism purposes for manned exploration of Jupiter's Galilean satellites:

Satellite Daily radiation rate (Sv) Yearly rate (Sv) Single-year limit 5-year cumulative limit Mild sickness LD 10/30 LD 35/30 LD 50/30 LD 60/30 LD 100/14 LD 100/7 LD 100/2
Io 36 13149 2 min 4 min 20 min 40 min 1.33h 2 h 2.67h 4 h 6.67h 33.33h
Europa 5 1972 13.33 min 26.66 min 2.22h 4.44h 8.89h 13.33h 17.78h 26.67h 44.44h -
Ganymede 0.08 29.22 15h 30h 6.25d 12.5d 25d 37.5d 50d 75d - -
Callisto 0.0001 0.037 1.37y 2.74y - - - - - - - -
The single year limit is 50 mSv, while the maximum 5-year cumulative exposure is 100 mSv (or 20 mSv per year). LD stands for Lethal Dose, LD x/y means "x" percent of individuals die within "y" days. LD 50/30 thus means half of people exposed at this level of radiation would die within 30 days. Some values have been omitted as the time required to reach the lethal dose level exceeds the time for lower lethal dose rates to be achieved or, in the case of Callisto, because it would simply be unreachable with the low radiation rate observed.

A few observations point to the obvious:

Astronauts on Io would experience fierce radiation flux, reaching their maximum cumulative radiation dose accepted by various safety regulations for a period of 5 years in only 4 minutes outside on the surface!!! Europa isn't much better, with less than half an hour of exposure. Ganymede is also a fierce environment, despite radiation being much less intense than at Io. With minimal shielding, Callisto would provide a safe working environment no worse than a nuclear power plant or research facility.

For shielding purposes to limit exposure to below regulatory levels for 5-year periods, the number of halving thickness of shielding material stands as follows:

Satellite Number of shielding layers Liquid water thickness
Io 20 3.6 m
Europa 17 3.06 m
Ganymede 11 1.98 m
Callisto 1 18 cm
As ice is less dense than water, about 10% more would be required.

I'll spare the details of what would happen to the exposed crews, you can read for yourself at Wikipedia!
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Old 05-17-2010, 07:02 AM   #2
SiberianTiger
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Might not be a problem for their kind...



(See Man After Man book by Dougal Dixon)
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Old 05-17-2010, 11:26 AM   #3
PhantomCruiser
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Quote:
Originally Posted by Cairan View Post
 ...a safe working environment no worse than a nuclear power plant or research facility.
Actually, working at a nuclear plant, I have less exposure per year than the average agricultural worker. Our dose rates are over-rated by various media outlets. Either that or they are under-reporting how much dose someone picks up by farming, working with and around fertilizers, or sunbathing all summer long...
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Old 05-17-2010, 11:32 AM   #4
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Quote:
Originally Posted by PhantomCruiser View Post
 Actually, working at a nuclear plant, I have less exposure per year than the average agricultural worker. Our dose rates are over-rated by various media outlets. Either that or they are under-reporting how much dose someone picks up by farming, working with and around fertilizers, or sunbathing all summer long...
I think they are just mostly working with conservative estimates, than real measurements. Also, if something goes wrong in your plant, your dose rate would be not so nice... and if you look at Germany, we have many older power plants, that go wrong often, and are kept running by electricity companies because they are effectively tax free now.

Maybe it is time to calculate a new modern exposure of nuclear power plant workers, with new safety standards and technology changing things a lot, but older power plants would still count as radiation hazard.
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Old 05-17-2010, 01:40 PM   #5
T.Neo
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What about active shielding? I know it is more far fetched at the moment, but what sort of advances would be needed for its implementation, and what sort of requirements would it have?
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Old 05-17-2010, 04:36 PM   #6
Zatnikitelman
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Originally Posted by T.Neo View Post
 What about active shielding? I know it is more far fetched at the moment, but what sort of advances would be needed for its implementation, and what sort of requirements would it have?
I think it depends on the radiation type. Now I'm nowhere near an expert on radiation physics, so take this for what it is.
Beta radiation would probably be the easiest to shield of the 4 classic radiation types (Alpha, Beta, Gamma, Neutron) because it is charged electrons and can be deflected by an electric charge or magnetic field potentially. A, G and N radiation though aren't as easily deflected due to their lack of charge IIRC. Shielding from these would require just that, physical shields blocking/absorbing the radiation.
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Old 05-17-2010, 05:46 PM   #7
T.Neo
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I thought Alpha particles were charged, being helium nuclei. May be a tad harder to deflect though.

Is a large portion of solar radiation/Jovian radiation not protons? Those carry a positive charge.

I don't think the Jovian radiation belts have any gamma or neutron radiation though. AFAIK free neutrons have a limited half-life, and gamma rays are just a type of photon.
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Old 05-17-2010, 06:25 PM   #8
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Quote:
Originally Posted by T.Neo View Post
 I thought Alpha particles were charged, being helium nuclei. May be a tad harder to deflect though.
Actually, alpha can be stopped by a sheet of paper, and beta by not much more.

It's the neutral stuff that's really penetrating.

Quote:
Is a large portion of solar radiation/Jovian radiation not protons? Those carry a positive charge.

I don't think the Jovian radiation belts have any gamma or neutron radiation though. AFAIK free neutrons have a limited half-life, and gamma rays are just a type of photon.
You're right. You may get a fair amount of X-rays from electromagnetic interactions in the belts though. I'm not sure.
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Old 05-17-2010, 06:34 PM   #9
Andy44
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So basically Walter Curnow and the crew of Discovery and Leonov would've been fried by the time they crossed between ships in the vicinity of Io. Another great Arthur C. story blown out of the water...sigh.
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Old 05-17-2010, 07:19 PM   #10
T.Neo
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Indeed.

But the radiation levels around Jupiter are nothing new... the Pioneer probes had problems with it, if I recall correctly.
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Old 05-17-2010, 07:44 PM   #11
Cairan
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Quote:
Originally Posted by PhantomCruiser View Post
 Actually, working at a nuclear plant, I have less exposure per year than the average agricultural worker. Our dose rates are over-rated by various media outlets. Either that or they are under-reporting how much dose someone picks up by farming, working with and around fertilizers, or sunbathing all summer long...
Indeed, K40 is radioactive, so standing around surrounded by potassium fertilizers must get their dose rates up in the end and outside without shielding from cosmic ray decay products... Then, to be fair, a fertilizer accident involving rapid combustion creates a lot less of trouble for the neighbors than the rapid fission of fuel in a nuclear plant. I guess that's where the perceived fear-factor about working in nuclear facilities come from.

But you are right, that is not how we perceive radiation risks with the media filter in place... I did not intend to further this perception, but merely to state that working on Callisto outside would be comparable to working in a nuclear plant, a "known" reference point.
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Old 05-17-2010, 07:47 PM   #12
Sky Captain
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I remember in the movie Voyage to the planets astronauts had a spacesuit with active radiation shielding. Is it even feasible to miniaturize such system to spacesuit level in real life?
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Old 05-17-2010, 08:11 PM   #13
T.Neo
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I doubt it. Both the creation of the active shielding and the power supply.
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Old 05-18-2010, 07:22 AM   #14
Cairan
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More information here: Hiding from Jupiter's Radiation

Quote:
The radiation belts are rotating around Jupiter faster than Europa does. This results in the radiation predominantly striking the trailing hemisphere of the moon—which is always the same portion of the moon since Europa is locked in a synchronous orbit around Jupiter. Moreover, there is a constant stream of micrometeorites landing on the leading hemisphere. These tiny rocks form a regolith layer up to 3 meters thick that could protect oceanic material from incoming radiation.
Therefore the best possible location for outposts would be buried in a few meters of ice either at the sub-Jovian point (where Jupiter is always above at zenith) or the opposite point so that you are neither affected by trailing hemisphere radiation flux or leading hemisphere micrometeroid. However, in the case of Callisto, I should point out that for some unknown reason, the particle flux hits on the leading hemisphere (See Magnetosphere of Jupiter).

As far as shielding goes, it should be in theory possible to reduce the bulk of shielding a lot if you can prevent beta particles (electrons) from smashing into the outpost external structure. This would prevent the Bremsstrahlung (braking radiation) x-rays from being given off by the electrons colliding with matter. I have no idea how powerful the magnetic field should be, but my guess is that T.Neo is quite correct in assuming no portable shield would be possible for a single astronaut. Maybe for a surface vehicule using charged supraconducting magnets or something like that, and definitely possible for a surface outpost if it's nuclear powered. Isn't it ironic to protect a colony from radiation by using power derived from radiation?

However, your beta-radiation/secondary x-ray shield generator would generate it's own problems, with torus of charged particles getting concentrated within the field lines, forming radiation belts just like they do in every planetary magnetospheres. Maybe orienting the field and poles parallel to the surface so that the belts are "floating" above the outpost would do the trick, and once in a while I guess the field could be dropped or reversed quickly to offload the charged particles accumulated in the artificial radiation belts of the electromagnetic shield.

---------- Post added at 03:22 AM ---------- Previous post was at 03:05 AM ----------

On a side-note, there was some confusion in the thread about alpha particles. These helium nuclei are positively charged and will also get bent by electromagnetic fields, opposite the beta particles (electrons). So I should myself have included alpha particles in the charged shield description. Alpha particles and protons (hydrogen nuclei) are also dangerous in the context of Jupiter as they cause a cascade of radioactive emissions when they collide at very high speed with matter: cosmic rays.
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Old 05-18-2010, 09:54 AM   #15
Richy
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As far as the strong radiation around Jupiter is caused by it's strong magnetic field, it should be possible to shield this via an other magnetic field.
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