Talk:Van Allen radiation belt

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See also: Talk:Van_Allen_radiation_belt/summary

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Firstly, the term "ring current" isn's specific just to Earth alone; it's a generic term, Jupiter for example also has a ring current. Van Allen belt, on the other hand, is Earth-specific, so when giving the composition of the ions trapped within it it seems more appropriate to me to put that information in the Van Allen article.

Also, you added the line "Electrons constitute the outer belt while protons form the inner belt." This is signficantly different from the previous material, which indicaed that the outer belt was composed of protons, alpha particles, and O+ ions. Where did you get that information? There's a contradiction now. Bryan

The previous material told me that the ring current contains such particles but I don't think it said anything really specific about the outer belt.

Protons are the most important component of the inner zone.

The peak electron fluxes in the outer zone exceed those in the inner zone by around one order of magnitude.

If you know this to be otherwise, feel free to change it. Lir 00:42 Nov 13, 2002 (UTC)

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Lir, you have been making many changes with unsatisfactory research. I don't have time to keep cleaning up after you personally. That's why I'm going to auto-revert changes that contain innacurate information. I suggest you do better prior research before making further changes. Feel free to pre-check proposed changes on Talk pages, which may save future edit wars. -- April 01:02 Nov 13, 2002 (UTC)

April. What is wrong with the article? Lir 01:03 Nov 13, 2002 (UTC)

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Blatant reverting is really dumb. Yes, Im well aware there are some things in that article Im not too sure about. If you know something I don't---then you better write about it or else your article wont be educational or informative--there are also things in the article that I have added and I dont think you disagree with---so reverting is stupid-you need to correct errors instead of avoiding them Lir 01:08 Nov 13, 2002 (UTC)

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Lir and April, both. Unless either of you link to resources about your "knowledge" of the Van Allen Radiation Belt from, NASA, JPL, the European Space Agency, a serous university doing research in the matter, or verifiable published (on paper) material, you are engaging in an edit war of your memoric recollections and this will quickly degenerate. Christopher Mahan

NO CHRIS. We are not engaging in a pointless edit war. We are engaging in a, "WHAT IS WRONG WITH MY ARTICLE SO WE CAN FIX MY ERRORS AND IMPROVE ON IT" rather than just deleting everything and not discussing anything. Lir 01:12 Nov 13, 2002 (UTC)

Lir, I'm inclined to side with April. She is a serious student of science, and you fool around a lot -- even more than zany guys like me :-)

Please cooperate with April. --Ed Poor

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Lir, nothing personal, but please leave comments alone. If you feel offended by something written, then please send a note to the author (it's called email) and ask them kindly to remove their comment or reword it. Christopher Mahan

Huh? Lir 03:37 Nov 13, 2002 (UTC)

moving stuff from Talk:Space elevator

This stuff seemed more relevant at Talk:Van Allen radiation belt than Talk:Space elevator. I hope you can use it on the main Van Allen radiation belt article.

I hope you cross referced it adequitly as it will be of interest to space elevator fans and perhaps should not have been moved.

The original author of Van Allen radiation belt obviously knows the subject better than I, but he got sloppy in places ie this paste: The electrons here have a high flux and along the outer edge and E > 40 Kev electrons can drop to normal interplanetary levels within about 100km (a decrease by a factor of 1000). This drop-off is a result of the solar wind -- DavidCary 10:19, 27 May 2004 (UTC) I think he is saying that certain allignments of the flux of ions from the Sun and the magntic flux allignment cause the temporary 1000 times drop off, but I don't know how to fix this sentence. Also he says the belt is diffuse, has high flux and high density which seems contradictory. Some approximate electons per cubic meter in each case would solve this problem if someone can estimate.

Van Allan belt problem

The Edwards elevator doesn't suffer Van Allen problems that notably because it is quite fast.

The Edwards elevator tether and climber may be little affected by Van allen radiation, but both is quite slow compared to the ions and compared to orbiting space craft in the Van Allen belts. The atomic oxygen does errode the CNT = carbon nano tubes, but I think atomic oxygen is mostly a problem at altitudes of less than 100 kilometers.

200km/h is slow. 3km/s is fast- but that's a rocket, not an elevator Wolfkeeper

200km/h is fast for a space elevator design.

Yes...

At worst, it'll be in the inner belt for about a day, suffering peak radiation only for a few hours.

That's very, very bad. Radiation sickness, teeth falling out, head swelling up, all kinds of bad. I mentioned somewhere- Apollo had about 1% of a dangerous dose; the space elevator goes 200x more slowly. Of course even partial shielding would help a lot; you might merely have a vaguely worrying dose.

Actually, according to the 25 Sv/year number listed in Van Allen radiation belt and the dose effects listed under radiation poisoning, you'd only run into serious problems (risk of death) if you stayed in the belt for a couple of weeks or more. A few days would give you an increased risk of cancer and hard-to-notice symptoms. This assumes 3 mm of aluminum as shielding, according to the article. --Christopher Thomas 23:45, 25 May 2005 (UTC)

Sounds wrong. The 2004 conference had a talk by Jorgensen. His conclusions are:

● Radiation field is severe.

● Shielding with Aluminum is not economical.

● Shielding with a magnetic field may be feasible

● Reducing dose by going faster is not very effective.

● Larger/Heavier climbers are more efficient when

shielding with a heavy material (contrary requirement

to talk by Ben Shelef).

● Climber mass and cost to orbit are impacted.

● Power requirement could be impacted.

As far as I know, he didn't look at the magnetic shielding in any massive detail; by all means check out the paper at: http://www.isr.us/spaceelevatorconference/FINAL_Conference_Presentations/Radiation/Jorgensen_Radiation.pdf

WolfKeeper

I've read the presentation slides, and I find the conclusions you drew from them rather odd. Specifically:

• The dose effects reported are consistent with the ones under radiation poisoning. The only difference is the exposure assumed.
• Aluminum looks quite effective at shielding. 3mm corresponds to the 10⁰ density region, which reduces dose to on the order of 100 rad (equivalent to 200 rem for protons), mostly from very-high-energy protons. This goes down roughly in proportion to the thickness of the shielding. Getting 10¹ g/cm² is no problem - this corresponds to walls 3 cm thick. Your cargo will still weigh much more than your capsule.
• The dominant form of radiation causing damage inside an aluminum can is very-high-energy protons. These are exactly the type of particles that magnetic fields are _bad_ at blocking, which is clearly illustrated on slide 16. If anything, their current values are underestimates, based on magnetic mirror and bending magnet calculations I did for other purposes. As a result, I question the presenter's conclusion that a magnetic solution would be feasible even if the mass of the cryostat for the superconducting coils was less than the mass of aluminum plating required for equivalent shielding. Slide 26 expresses reservations about feasibility, which don't seem to have made it to slide 30.
• The conclusions on slide 30 state that going faster doesn't help much, but the plot on slide 27 seems to indicate a linear or superlinear benefit vs. shielding mass for any reasonable elevator speed, making that conclusion questionable. Absolute dose to be shielded against is intrinsically linear with respect to travel time, so this conclusion seems puzzling on several levels.

Sure, the radiation dose is inversely proportional to speed, but you'd have to go awfully fast to make a really big difference. WolfKeeper

In order to make a space elevator cost less than conventional launch, you already have to go awfully fast. The total cargo in transit at a given time is at most comparable to the weight of the elevator, and possibly much less (depends on how much of a safety factor you can afford to build into the elevator; if it's near materials limits, the answer is "not much"). --Christopher Thomas 08:11, 28 May 2005 (UTC)

In summary, while it doesn't look healthy to ride a lightly-shielded elevator _regularly_, a single trip doesn't look particularly lethal, and conventional shielding seems to be the best approach to reducing exposure for a given elevator geometry.

I really don't think you can give passengers radiation sickness.WolfKeeper

That depends on how badly the passengers want to go into space. If they plan to make a single trip, it'll give them an increased risk of cancer down the road, and not much else. I'm sure you can name people who'd buy a ticket. I can. --Christopher Thomas 08:11, 28 May 2005 (UTC)

The _most_ effective approach seems from the slides to be to construct the elevator off-equator, so as to not intersect much of the lower belt. --Christopher Thomas 19:51, 26 May 2005 (UTC)

Only maybe. I haven't seen how much extra cable mass building a 47 degree offset cable needs. It seems substantial, but I don't know how substantial.WolfKeeper

You can actually calculate this pretty easily. The curved elevator will be shorter than the piecewise-linear shape formed by the tangent from the anchor point, and a line drawn from the earth's centre of mass to the far terminus. The change in distance works out to under 3000km for sane geometries. The pertinent question is how much extra tapering this gives. At 120 GPa/density 3, it's a factor of 2. At 60 GPa, it's 4, and it's 8 at 30 GPa. For a fixed earth-bound terminus size, this is the factor by which the elevator gets heavier, but if you instead assume that your cargo transfer rate is not limited by the terminus size/load capacity (but instead the whole cable's weight), you get almost no weight increase (as the length increase occurs on the most tapered part of the cable). Which scenario is the case depends on the design of the cable and how fast you can make elevators run at various altitudes. --Christopher Thomas 08:11, 28 May 2005 (UTC)

You should probably check out Blaise Gassend's paper on non-equatorial cables. In particular he claims that the length is mostly irrelevant (I'm not 100% convinced by his argument on this), but more importantly he makes the point that off-equatorial cables inevitably have high tension at the attachment point. This aligns more closely with the qualitive analysis I have done too. I'm therefore fairly sure that your calculation is incorrect, since you haven't taken that effect into account. Still, Blaise's calculation is somewhat flawed as well, since he takes a equatorial cable and moves it north, rather than reoptimising it, and he figures on a payload of 0% at 48 degrees which is very pessimistic. Even so, the hit is clearly substantial; so I'm left wondering whether off-equatorials are worth it in fact, it may be better to just double a equatorial cable up and use the extra 100% payload for more shielding, although that too can have negative implications on power beaming.WolfKeeper

My calculations are an approximation, but a reasonably good approximation. To get the correct values, you'd have to numerically integrate a fairly nasty set of equations, but the upshot is that because only a very small fraction of the cable's mass is under additional tension, I wouldn't expect it to have a large impact on the cable's size. If anything, my values should be overestimates, as I took an upper bound on the cable length (the curve will be shorter than the piecewise-linear version), and assumed that all of the added length was being pulled down at 1g (in practice it's high enough up for forces to be lower). In the worst case, though, tension in the non-equatorial segment would average about 1.5 times what you'd expect from a vertical cable, making the characteristic length 1.5x shorter, giving you about a factor of 3, 8, and 64 for 120, 60, and 30 GPa if terminus-limited, using pessimistic overestimates for safety. If you aren't terminus-limited, then it's again a non-issue, for reasons mentioned previously (cargo on the elevator at any one time is proportional to the mass of the elevator, meaning a thinner terminus doesn't hurt you). --Christopher Thomas 03:41, 29 May 2005 (UTC)

But there seems to be a serious error in the paper. He says on one page that the amount of equipment needed to do lifesupport for humans may be about 20 tonnes. However, he fails to take account of the potential shielding effects of this equipment; by carefully arraying it around the passenger areas you may be able to get *great* shielding. That's a big screw-up IMHO. Of course the economic argument may very well be true, but it looks to me that his conclusions on the effectiveness relate to the economics, rather than the radiation. And the economics may be self-reinforcing here- if humans can safely go up it they may do it a lot, and then the economics of elevators tend to improve. I'm actually slightly more optimistic.WolfKeeper

It sounds like he's assuming a very large number of passengers. Food and water for a week for one person weighs about 20 kg, tops. Oxygen for that time weighs at most about triple the weight of the dry component of the food (say 20 kg oxygen, tops). That gives you 40 kg of supplies per week per 100 kg of passenger-plus-carry-on-baggage. For trips lasting a week or less, the vast majority of the mass is the passengers (not counting shielding). If you're using consumables as shielding, you'd probably just use a double hull and fill it with water (sewage basin somewhere in there too; it can be recycled topside, or dumped downside). You'll need a lot more mass than this for shielding for practical car sizes, though (assuming 10¹ g/cm²). You'll want aluminum and kevlar for micrometeorite shielding, anyways. --Christopher Thomas 08:11, 28 May 2005 (UTC)

Apollo astronauts received most of their dose from GCR (Galactic Cosmic Radiation) and solar particles unrelated to the Van Allen belts. Apollo also had nothing that was specificly "shielding"; they had the aluminum skin (being a metal, it has problems with Bremsstrahlung radiation, but with a low atomic number, it's not *too* bad as insulation), and probably the biggest amount of absorption from the fibrous insulation. Any system where there was serious worry about radiation, however (for example, a mars mission) proposes using plastics (such as LDPE) or liquid hydrogen as physical shielding. There was no particular reason for serious shielding, if only for the fact that Apollo hardly touched the belts (due to that whole "earths rotation not matching up with the shape of the radiation belts" thing that you keep forgetting about) Rei 21:11, 26 May 2004 (UTC)

Kinda, Apollo chose the trajectory to deliberatly miss the worst of them. Spacecraft have infinitely more choices; elevator cars have very few.--Wolfkeeper 00:03, 27 May 2004 (UTC)

At best launching times, it will bypass the vast majority of the belt alltogether. Rei 21:07, 25 May 2004 (UTC)

Doubtful; the earth spins taking the cable and car with it back into danger. The magnetosphere is lopsided due to the solar wind. Apollo was able to do it fast, and could in a very real sense 'step off' the earth and get lobbed through only the very edge of the belt. Apollo had *much* more latitude.

It is in the inner (high intensity) belt for hours, and in the outer belt (low intensity) for (~2 days?). Some other designs for elevators are slow, however, and take as much as weeks, so this section needs to be included.

Also, I think you have some misconceptions about Edwards' design. He placed a much higher priority on getting payload up than down, assuming that is what most business would want. While I'm not sure I agree with that assumption, it is an elevator optimized for that particular task. Any payload going down is payload not going up (well, actually, it's not that simple - timing comes into play, because different parts of the cable have different amounts they can hold, but you get the picture). Rei 15:46, 25 May 2004 (UTC)

AFAIK, the only guaranteed solution is make the cable a lot thicker and just live with the extra shielding.

Active shielding? I asked this question at the last but one Space Access conference to Henry Spencer; who is an expert on space (he was lecturing on the physics of the Van Allen belts at the time). His response was 'it has been looked into, but does not work'. The nearest thing to that is the HiVolt proposal; that's sort of what that is. Unless Rei or anyone else can come up with a reference of how that would work for Elevator cars, I will remove this; as it is extremely speculative at best (this is an encyclopedia dammit!)

Wolfkeeper

How would active shielding "not work"? You're the one who's insistant on references: provide a reference, please - preferably one that explains why it doesn't work. Rei 23:47, 25 May 2004 (UTC)

Not until you provide a reference that shows it *does* work. There's a world of difference between Solar Wind/Flares and the Van Allen belt. One consists of supersonic gas and plasma, the other is charged particles trapped in a magnetic field.

Exactly how do you know that superimposing another magnetic field on top of the Earth's magnetic field doesn't make the radiation worse? (I actually think it would- think about how the Earths poles are regions of much higher radiation, the charged particles actually follow lines of magnetic flux. Here's a hint: you don't.

This is done routinely. It's called a magnetic mirror, and is part of many plasma confinement geometries, among other things. I doubt it'd work for a practical elevator car, but that's not because the principle is unsound - it's because you'd need either an extremely strong field or a very large weaker field to adequately deflect ions with energies of tens of MeV. A variant of this idea was proposed for shielding Stanford torus style space habitats. --Christopher Thomas 23:45, 25 May 2005 (UTC)

Until you can come up with a sensible reference to this being applied in LEO as a defense to the Van Allen belt in general, or even better used on the Space Elevator in particular, this piece is going in 3 days time. You are not a designer of Space Elevators, you are at best an author working on an article writing about it. Wolfkeeper

And you are a user relying on threats to push information through. I just added two *MORE* references to it, to prove that it is effective against the Van Allen belts. The reference count is now three ZERO. You don't remove referenced material with ZERO references, Wolfkeeper.

You have zero references relating it to the subject of Space Elevators. This is not a page where Rei designs the best elevator or active radiation shielding; this is where you cover the existing knowledge on Space Elevators. You are not a worker in this field. If you can't get this simple fact, then I fail to see why you are even here.

You clearly know absolutely nothing about the topic,

Wrong! :-)

so let me enlighten you. First off, read the wikipedia article on the Van Allen belts. The particles are trapped in a so-called "magnetic mirror". This is due to Lorentz forces. When a charged particle moves through a magnetic field, it experiences a force tangential to both the magnetic field and the direction of motion (this is used to good advantage in Penning traps). Consequently, if you create a magnetic field around a spacecraft in the Van Allen belt, any particles moving through the field will be deflected tangential to the field and the particle's direction of motion.

For it to be *effective* shielding the shielding has to actually work on an elevator car. For that the mass must be right, the power supplies must not be too arduous, it must not interact in bad ways with the (conductive?) cable itself (hint: eddy forces), the R&D to produce a working system must not be too high; and it should have a predictable development time, not be too expensive or unreliable etc. etc. etc. It seems to me you've come up with a strawman proposal that active shielding be used; it may very well work, but it does not seem to have gone through any review whatsoever- and you- who just pulled it out of thin air- are proposing that it be placed straight in an encyclopedia! No, that's not right; that's not the way it works.--Wolfkeeper 00:03, 27 May 2004 (UTC)

According to studies, active shielding methods proposed thusfar are effective for protons of energies up to 200 MeV; the high energy inner belt has protons of energies 10-100MeV.

I see absolutely no evidence that Brad Edwards is proposing to use active shielding for the Space Elevator.--Wolfkeeper 00:03, 27 May 2004 (UTC)

Upon reflection, and having read the references, I have left the clock running; I'm not opposed to it staying here *if* you can link it back to the Space Elevator in some way.--Wolfkeeper 00:03, 27 May 2004 (UTC)

Consequently, active shielding is a very realistic option for the inner belt.

And Rei is unanimous in this :-)

The outer belt is weaker.

Magnetic field making the radiation worse?

Rei 16:47, 26 May 2004 (UTC)

Actually that can happen. On the Earth close to electricity pylons you find that the cosmic radiation has scattered off the E-M field and increased the radiation around it. It's measurable.

--Wolfkeeper 00:03, 27 May 2004 (UTC)

Citations? The magnetic fields produced by high-tension power lines are quite weak any significant distance away from them. You'd need a multi-Tesla field to substantially deflect cosmic rays energetic enough to penetrate the atmosphere over that short a distance. --Christopher Thomas 23:45, 25 May 2005 (UTC)

• I'm moving the space elevator stuff back to space elevator (even though that is a bit long too). I left the part on HiVOLT here, although it's a little out of context where I left it.