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#21
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Radiation a Mars trip hazard?
In article ,
Remy Villeneuve wrote: ...A dense outer shell should try not to stop the particules but refract or reflect them... Unfortunately, there are no materials that refract or reflect high-energy protons to any significant extent. ...like a stealh fighter mostly reflects radar (F-117), or an X-ray telescope focuses incoming photons. Stealth aircraft actually work fairly hard at *absorbing* radar; as an extra, they try to concentrate any remaining reflection in a few specific directions. X-ray telescopes focus photons only from one very specific direction. Solar-flare protons, unfortunately, orbit the local magnetic fields of the proton cloud and hence come from all directions. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#22
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Radiation a Mars trip hazard?
In article ,
Remy Villeneuve wrote: ...A dense outer shell should try not to stop the particules but refract or reflect them... Unfortunately, there are no materials that refract or reflect high-energy protons to any significant extent. ...like a stealh fighter mostly reflects radar (F-117), or an X-ray telescope focuses incoming photons. Stealth aircraft actually work fairly hard at *absorbing* radar; as an extra, they try to concentrate any remaining reflection in a few specific directions. X-ray telescopes focus photons only from one very specific direction. Solar-flare protons, unfortunately, orbit the local magnetic fields of the proton cloud and hence come from all directions. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#23
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Radiation a Mars trip hazard?
[snip]
Stealth aircraft actually work fairly hard at *absorbing* radar; as an extra, they try to concentrate any remaining reflection in a few specific directions. X-ray telescopes focus photons only from one very specific direction. Solar-flare protons, unfortunately, orbit the local magnetic fields of the proton cloud and hence come from all directions. Thanks for the enlightment, as usual! Bottomline is: you have to absorb it one way or another. |
#24
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Radiation a Mars trip hazard?
"Dr. O" wrote in message ...
http://www.nytimes.com/2003/12/09/sc...ce/09RADI.html The thing I don't understand is that people have been spending much more time in orbit than the round-trip to Mars. Although the upper atmosphere does shield them somewhat, the majority of the radiation is still getting through. Why are they so concerned then about radiation? Also, lead shielding will have to be installed in any Mars spaceship anyway because of the possibility of solar flares. I'll try this again - my posts seem to be routinely ignored. Ah well. The Earth's magnetic field traps a lot of the charged particle radiation that emanates from the Sun. Flights into space that fly below this field are protected from the brunt of radiation found in interplanetary and cislunar space. Information about your query can be found at the following site; http://radhome.gsfc.nasa.gov/radhome/papers/seeca3.htm http://books.nap.edu/books/030905698...5.html#pagetop http://content.aip.org/APCPCS/v246/i1/130_1.html Basically, the Van-Allen radiation belt sheilds astronauts in Low Earth Orbit from deadly solar and charged cosmic radiation. Since rocket boosters are limited in terms of speed and size, their payloads must be miminum and travel along slow minimum energy orbits. So called hohmann transfer orbits http://www.ucar.edu/eo/staff/dward/s...s/appendix.htm These orbits take years to complete, and if you're sending people, you need to execute them twice! Once out another back. So, folks will be exposed to a minimum of 2.5 to 3 years to very high levels of radiation - or more. This pushes their exposure up past 130 Rems - if they're well sheilded, and far higher, if they're not! http://srhp.jsc.nasa.gov/project/BNL.htm NASA and Brookhaven together was able to show that even for a trip to Mars, which is our neighbor in interplanetary space, there is a real risk that some if not all of the astronauts would suffer ill effects from radiation, and if sheilding were not available, may not survive the trip! Lead sheilding is heavy even lighter sheilding adds up. Even so, one can imagine that with robotic systems pre-placed on Mars before their arrival, it may be possible to send astronauts encased in sufficient sheilding, who operate throughout their ship and beyond via telepresence. http://ranier.hq.nasa.gov/teleroboti...an/Chap2g.html http://www.foresight.org/Updates/Upd...pdate08.2.html Radiation hazards are very much the outcome of small payloads and low final rocket velocities. Larger and more capable rockets will change this. Large, fast moving, heavily sheilded vehicles wouldn't require special sheilding. Its only small, slow moving, lightly constructed vehicles that have this problem. http://www.astronautix.com/lvfam/orion.htm http://www.astronautix.com/articles/probirth.htm http://science.nasa.gov/newhome/head...p12apr99_1.htm The nuclear pulse rockets described in the source material above are capable of flying large heavily constructed, adequately sheilded throughout, spacecraft on high-speed orbits throughout the solar system. This is the way to go in space. (1) set up launch centers at radiation waste sites and old bomb test sites throughout the world; (2) convert all nuclear weapons centers into nuclear pulse manufacturing sites; (3) use current inventory of nuclear materials as fuel source for a small fleet of very large spacecrft; (4) fly off the nuclear material and deposit remotely operated labs t throughout the solar system - involving a fleet of dozens of ships and tens of thousands of astronauts; (5) return to the moon, where a long term base is established and reusable chemical rockets maintain contact with Earth; (6) establish an international nuclear research center on the moon, and continue the advance of nuclear pulse rockets, as well as space based defense research to enforce an enhanced nuclear nonproliferation regime on Earth and in space; This will not only address radiation hazards on a Mars trip, but also significant radiation hazards on Earth! |
#25
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Radiation a Mars trip hazard?
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#26
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Radiation a Mars trip hazard?
In article ,
Christopher wrote: Bottomline is: you have to absorb it one way or another. Couldn't the spacecraft have it's own magnetic field? To be a useful barrier to incoming particle radiation, the field would have to be immensely strong or would have to extend over a huge distance (which means either making it immensely strong at the source, or generating it with a physically very large structure). It's possible in theory but impractically hard in practice, at least for now. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#27
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Radiation a Mars trip hazard?
Henry Spencer wrote:
Couldn't the spacecraft have it's own magnetic field? To be a useful barrier to incoming particle radiation, the field would have to be immensely strong or would have to extend over a huge distance (which means either making it immensely strong at the source, or generating it with a physically very large structure). It's possible in theory but impractically hard in practice, at least for now. To put some numbers on this... To deflect particles of a given energy, the strength of the magnetic field B is inversely proportional to the linear dimensions of the field (assuming identical geometry). Since the stored magnetic energy is proportional to volume * B^2, the total energy stored in the magnetic field will scale in proportion to the linear dimensions of the protected volume. The Earth's magnetic field outside the atmosphere has a stored energy equal to about that of a 200 megaton bomb. To similarly protect a 12 meter sphere (as opposed to a 12,000 km sphere) would require a magnetic field with the energy of a 2 kiloton bomb. (This is probably overkill, though.) Paul |
#28
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Radiation a Mars trip hazard?
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#29
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Radiation a Mars trip hazard?
Couldn't the spacecraft have it's own magnetic field?
To be a useful barrier to incoming particle radiation, the field would have to be immensely strong or would have to extend over a huge distance (which means either making it immensely strong at the source, or generating it with a physically very large structure). It's possible in theory but impractically hard in practice, at least for now. Let's turn this around the other way... If we can't deflect it, can we direct it? What about making a large magnetic field by creating a large cage around the ship? Doesn't use much mass and you get a large field. But it would need to be strong enough to maintain shape while the ship accelerates. A large magnetic field could use little energy to deflect radiation and create a radiation free area. |
#30
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Radiation a Mars trip hazard?
Toprope wrote:
What about making a large magnetic field by creating a large cage around the ship? Doesn't use much mass and you get a large field. But it would need to be strong enough to maintain shape while the ship accelerates. A large magnetic field could use little energy to deflect radiation and create a radiation free area. Won't effect neutrons, won't deflect high-energy photons. High-energy photons hit the ship, you get a cascade of other high-energy particles. |
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