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Zachary
2003-Dec-11, 08:11 PM
I'm just curious. I know the first belt is fairly near the Earth, and I'm wondering if most spacecraft today have to pass through it? I remember hearing somewhere that just to get into orbit you had to pass through it. Is this true or am I just talking gibberish? ](*,)

Cheers,
Zachary

ToSeek
2003-Dec-11, 08:19 PM
The lower belt stays above 400 km, which is where the space station orbits. The shuttle usually orbits at that altitude or lower.

How is it possible for manned space flights to survive the effects of the Van Allen Belts? (http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970630a.html)

Zachary
2003-Dec-11, 08:24 PM
The lower belt stays above 400 km, which is where the space station orbits. The shuttle usually orbits at that altitude or lower.

How is it possible for manned space flights to survive the effects of the Van Allen Belts? (http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970630a.html)

but....but....the ISS doesn't have a 5 foot thick lead lining! :o :P

ToSeek
2003-Dec-11, 08:32 PM
The lower belt stays above 400 km, which is where the space station orbits. The shuttle usually orbits at that altitude or lower.

How is it possible for manned space flights to survive the effects of the Van Allen Belts? (http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970630a.html)

but....but....the ISS doesn't have a 5 foot thick lead lining! :o :P

That makes it much easier to have a good barbecue. ;)

JayUtah
2003-Dec-11, 08:35 PM
The geometry of the Van Allen belts varies according to the 11-year cycle, and according to prevailing solar weather. Spacecraft in the higher altitudes of LEO will occasionally encounter the lower portions of the inner Van Allen belt. This is the situation that faces the ISS periodically.

The ISS uses several inches of high-density polyethylene in the living quarters as shielding against influx from the Van Allen belts.

Zachary
2003-Dec-11, 09:02 PM
The geometry of the Van Allen belts varies according to the 11-year cycle, and according to prevailing solar weather. Spacecraft in the higher altitudes of LEO will occasionally encounter the lower portions of the inner Van Allen belt. This is the situation that faces the ISS periodically.

The ISS uses several inches of high-density polyethylene in the living quarters as shielding against influx from the Van Allen belts.

What kind of radiation does the belt mainly consist of? And for how long did Apollo 11 have to travel through the belt?

JayUtah
2003-Dec-11, 09:42 PM
There are two broadly defined Van Allen belts. In the inner belt you find energetic protons, energetic electrons, and alpha particles. In the outer belt you find primarly energetic electrons.

The passage through the significant parts of the Van Allen belts took about four hours. But since the intensity of the radiation was different at each point along the path, it's difficult to use that figure to arrive at an analytical estimate of exposure.

Shielding against alpha particles is trivial. A sheet of cardstock typically does the trick. Shielding against energetic protons is rather easy as well, since these are large, heavy particles that tend not to penetrate most solid materials except at very high energies. Shielding against electrons is more difficult, but is best accomplished by non-metallic materials. There is not as great a need to shield against electrons, however, since their biological effect is limited compared to that of the heavier particles.

Sigma_Orionis
2003-Dec-11, 11:26 PM
IIRC the "5 inch thick lead lining" is needed for Gamma radiation which is composed of electromagnetic waves, not particles.

JayUtah
2003-Dec-11, 11:39 PM
Yes, electromagnetic radiation in the ionizing wavelengths (generally anything shorter than visible light) requires thicker/denser shielding as wavelength decreases. Comparing the Van Allen belts to Chernobyl or Hiroshima is utterly unfounded.

Sigma_Orionis
2003-Dec-11, 11:52 PM
Yes, electromagnetic radiation in the ionizing wavelengths (generally anything shorter than visible light) requires thicker/denser shielding as wavelength decreases. Comparing the Van Allen belts to Chernobyl or Hiroshima is utterly unfounded.

Quite true, of course HBs conveniently forget to mention it while making their claims....

dgavin
2003-Dec-12, 04:58 AM
Here is something i worked up in response to Fox's lunar conspiracy show some years ago about the Van Allen Belts.

The information presented here was gleened from two universities that have no tie in's with NASA.
The Van Allen Belt(s) are two cresent shaped belts of radiation orbiting the earth's equator in a tourus that vary in intensity dependant upon the 11 year solar flare cycle. At the height of the cycle a third ring may or may not form even closer to earth inside the orbit of the first.
On average the first ring's electron and proton emissions was mesured at 10KeV's, and the outer ring at 30MeV's, an eV is an electron volt, which corresponts to about 1.60219 to the 10th to -19th power Joules, or 0.000000000000000000160219 Joules. A Joule is equivielent to a watt second. 10KeV computes out to .0000000000000000000000000445052777777777813382 Kilowatt hours.
30MeV's computes out to 0.00000000000480657 Kilowatt hours.
Now to consider an X-Ray machine a few of which I hit manufacturer site for specs, for the most part they draw around 2000 watts at 440 volts AC. Total radation exposure on X-Ray machines is about 10 milirems per exposure(1 second). Just a fraction of the 2 rems allowed per year. Even considering that natural production of radiation is usually about 10 times more efficient then artificial, The Van Allen belt doesn't come near to the power levels to generate any lethal dose of radiation. It took the Astronauts about an hour to cross through each belt. The total energy their ship would of been exposed too in the larger belt would be .000146 Watt hours. Given that not all this energy is in the form of radation, only a fraction of it, at best the Astronauts were exposed to less then .1 milirems a second. 360 milirems for the hour to pass through the belt. A person living in High altitudes say like in Denver, recives about 330 milirems a year from particles that make it through our atmosphere.
In Essence, the larger Van Allen belt Exposed the Astronauts to about a year worth of high altitude radiation in an hours times. Not that major of a deal, considering it takes 500 rems to outright kill someone. They would have to of been in the Van Allen belts for 13,888,000 hours to get an 500 rem dose.
I'd like to mention I got all these facts from non NASA, and some medical equipment sites, and from there just did some simple math. A little honest research will go to long way.

Mellow
2003-Dec-12, 10:42 AM
mate,

thats an excellent piece of research, it's impressive wht clever people can do with a little aplication. I hope you don't mind if I borrow that?

Ta

Waarthog
2003-Dec-12, 12:18 PM
duplicate... sorry

Waarthog
2003-Dec-12, 12:28 PM
A little honest research will go to long way.

Herein lies the quandry. The last thing the twinkies want to do is honest research. If they do, then their time of fame and glory (in their eyes anyway) ends. The money dries up, everyone goes home. So it is in their best interest not to do any honest research or to apply simple scientific methods. As for those not making money from it, they too are in the same trap. I have been reading of late on James Randi's site about what he has coined the "Henrietta syndrome" about people who need to believe things so badly that they are willing to overlook the most obvious evidence to the contrary. The Lunar Hoax Conspiracy falls into that category and is less about physical sciences than psychology when it comes right down to it. Those who both preach and follow, do so from a need to feel something superior to others. Believing themselves to have knowledge that others do not have allows them to feel above others. This becomes self reinforcing when they take the track that that only people lesser than themselves (the sheep so to speak) still carry a contrary opinion. From an ego standpoint, this is powerful fuel.
We can debunk until we are blue, holding off the armies of Mordor :) but those who need to believe this for their own personal validation are lost causes. As been said before however, those types of people are not the true audience of this site but rather those who have honest questions and who do not know how to separate the slickly packaged manipulation that passes for reseach from the twinkie crowd.

Glom
2003-Dec-12, 12:55 PM
Jay summed up many of the reasons for compulsion (http://www.clavius.org/why.html). The truth is that the Conspiracy Theory is powerful. It corrupts the hearts of otherwise good people.

AstroSmurf
2003-Dec-12, 01:00 PM
Interesting method, dgavin. The only part I'm missing out here is how you went from the average energy per particle to the total radiation energy throughout the passage. You need to have the flux as part of your equation, otherwise your results will be way off.

The result seems a few orders of magnitude too low. I would have estimated approximately half a year for a 500 rem exposure, given median radiation levels. 13,888,000 hours is over 1,500 years...

dgavin
2004-Jul-04, 07:28 PM
Interesting method, dgavin. The only part I'm missing out here is how you went from the average energy per particle to the total radiation energy throughout the passage. You need to have the flux as part of your equation, otherwise your results will be way off.

The result seems a few orders of magnitude too low. I would have estimated approximately half a year for a 500 rem exposure, given median radiation levels. 13,888,000 hours is over 1,500 years...

Sorry took so long to get back to this. I found conversion tables from Electron Volt into Joules, (or a Watt Second), once had energy expessed in watt seconds it was simple to fugure exposer over time.