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Swift
2013-Jun-12, 02:29 PM
From R&D magazine (http://www.rdmag.com/news/2013/06/moon-radiation-findings-may-reduce-health-risks-astronauts?et_cid=3308053&et_rid=54734303&location=top)

Space scientists from the Univ. of New Hampshire (UNH) and the Southwest Research Institute (SwRI) report that data gathered by NASA’s Lunar Reconnaissance Orbiter (LRO) show lighter materials like plastics provide effective shielding against the radiation hazards faced by astronauts during extended space travel. The finding could help reduce health risks to humans on future missions into deep space.

Aluminum has always been the primary material in spacecraft construction, but it provides relatively little protection against high-energy cosmic rays and can add so much mass to spacecraft that they become cost-prohibitive to launch.

The scientists have published their findings online in Space Weather. The work is based on observations made by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on board the LRO spacecraft. Lead author of the paper is Cary Zeitlin of the SwRI Earth, Oceans, and Space Department at UNH. Co-author Nathan Schwadron of the UNH Institute for the Study of Earth, Oceans, and Space is the principal investigator for CRaTER.

Says Zeitlin, “This is the first study using observations from space to confirm what has been thought for some time—that plastics and other lightweight materials are pound-for-pound more effective for shielding against cosmic radiation than aluminum. Shielding can’t entirely solve the radiation exposure problem in deep space, but there are clear differences in effectiveness of different materials.”

Like they said in The Graduate: I have one word for you; Plastics! ;)

Ara Pacis
2013-Jun-12, 03:45 PM
This is news? I thought we've known this for at least a decade. The problem with using plastics is where to get it. Currently, we'd have to get it from earth, and the low density means it would take up a lot of room on a rocket. I don't think we can source plastic from asteroid or lunar mining either, unfortunately.

Nick Theodorakis
2013-Jun-12, 05:46 PM
In biochemistry and molecular biology research labs, where it is (or was, "back in the day") common to use hard beta emitters, plexiglas/perspex has long been considered the most appropriate shielding material for those isotopes.

Nick

Swift
2013-Jun-12, 06:35 PM
This is news? I thought we've known this for at least a decade. The problem with using plastics is where to get it. Currently, we'd have to get it from earth, and the low density means it would take up a lot of room on a rocket. I don't think we can source plastic from asteroid or lunar mining either, unfortunately.
I think this is what is new (from article):

The space-based results were a product of CRaTER’s ability to accurately gauge the radiation dose of cosmic rays after passing through a material known as “tissue-equivalent plastic,” which simulates human muscle tissue. Prior to CRaTER and recent measurements by the Radiation Assessment Detector (RAD) on the Mars rover Curiosity, the effects of thick shielding on cosmic rays had only been simulated in computer models and in particle accelerators, with little observational data from deep space.

The CRaTER observations have validated the models and the ground-based measurements, meaning that lightweight shielding materials could safely be used for long missions, provided their structural properties can be made adequate to withstand the rigors of spaceflight.


As far as I can see, sourcing it from off-Earth is another issue. At the moment we have the actual ability to make no space-sourced materials for either rockets or habitats. However, if one has a carbon source, one could find a way to make plastics.

JohnD
2013-Jun-12, 10:19 PM
The point would be, not to have the plastic "take up a lot of room in the rocket", but to make the rocket out of plastic.
And Nasa Science News made exactly the same points as long ago as 2005:
http://science.nasa.gov/science-news/science-at-nasa/2005/25aug_plasticspaceships/
Then, a "polyethylene-based material called RXF1 that's even stronger and lighter than aluminum" was reported, with "superior structural properties with superior shielding properties" to aluminium.

I can't find anythng about why this wonder material isn't in use. Maybe organic materials, both living and non-living, suffer from the effects of radaition in that they are damaged by it. There are some remarks about RFX1 becoming brittle if radiated.

JOhn

Ara Pacis
2013-Jun-13, 01:40 PM
The point would be, not to have the plastic "take up a lot of room in the rocket", but to make the rocket out of plastic.
And Nasa Science News made exactly the same points as long ago as 2005:
http://science.nasa.gov/science-news/science-at-nasa/2005/25aug_plasticspaceships/
Then, a "polyethylene-based material called RXF1 that's even stronger and lighter than aluminum" was reported, with "superior structural properties with superior shielding properties" to aluminium.

I can't find anythng about why this wonder material isn't in use. Maybe organic materials, both living and non-living, suffer from the effects of radaition in that they are damaged by it. There are some remarks about RFX1 becoming brittle if radiated.

JOhn

Making the rocket out of plastic is a first step to reducing Bremsstrahlung, but it may not be enough. IIRC, you need more than a few milimeters of thickness, you need close to a meter in thickness.

Ara Pacis
2013-Jun-13, 01:41 PM
As far as I can see, sourcing it from off-Earth is another issue. At the moment we have the actual ability to make no space-sourced materials for either rockets or habitats. However, if one has a carbon source, one could find a way to make plastics.

I thought it was finding the hydrogen that was the problem.

JohnD
2013-Jun-13, 10:48 PM
Ara Pacis,
And?
Please expand your argument.
JOhn

Ara Pacis
2013-Jun-14, 05:13 AM
Ara Pacis,
And?
Please expand your argument.
JOhn

Which one?

Arguing that a particular use of a new plastic is as strong as aluminum and has the added benefit of not producing Bremsstrahlung and even blocking a non-zero amount of regular radiation does not mean that that same amount of plastic is good enough to protect against the radiation environment of space for a journey beyond our magnetosphere. More radiation in an environment and more time spent in that environment means more shielding protection factors will be required, no matter what it's made of.

FarmMarsNow
2013-Jun-15, 06:17 AM
Perhaps the solution to the shielding problem could be addressed with silica and minerals without having the scrounge for carbon.

Has anyone heard of Nanostop fabric and Natcoresolar paint? It uses nano-tubes and silica to block x-rays for lightweight x-ray shielded clothes. It can also be mixed into paint. (Yes, the 'Nanotubes' are carbon, but they may ultimately not be necessary in a similar product.)

Also, years ago I read that suspending minerals in plastics or rubber can block various high energy light wavelengths. It was a long time ago and don't remember where I read it, but it makes sense. Choose appropriate minerals to diffract and absorb the wavelengths that you don't want and suspend them in a matrix. This could save on weight and could be used in combination with standard metal hulls to make a composite hull that could be much thinner than the 1 meter plastic hull that someone mentioned before. It would also be more likely that the materials would be available on asteroids.

kzb
2013-Jun-19, 05:30 PM
Apparently, stretching a sheet of graphene causes the electrons in its structure to experience a "pseudomagnetic" field of 300 Tesla.

I wonder if this could be used to repel charged particles in some way ? Graphene sheets would be far lighter than electromagnets.

http://newscenter.lbl.gov/news-releases/2010/07/29/graphene-under-strain/