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Fly To Mars In A Plastic Ship
saskboy writes "NASA reports that an old polymer may be the spaceship material of the future. Polyethylene is in household garbage bags, and it is also an effective solar radiation shield. I learned three years ago in astronomy class that polyethylene is used in the sleeping quarters on current orbiting space vehicles, but now NASA has developed a way to toughen the polymer into a product they call RXF1 which is 'even stronger and lighter than aluminum'. As you may know, radiation in space is currently a major obstacle to manned missions outside of the Earth's magnetic field, so better radiation shielding is essential to planned manned missions to Mars and beyond.
Get the mp3 podcast of the article here."
RSS URL is feed://science.nasa.gov/podcast.xml, smartass
I am subscribed with the iPodder app. Again, how is this not a podcast?
--- Eat my sig.
Just taking a look at TFA, it's quite clear that this is a link to an audio file (actually an M3U PL) rather than any mention of a podcast.
This would suggest the file is intended for listening by anyone, anywhere with a Mpeg 3 player thethered or not.
It seems that the term podcast in this case was applied solely by the submitter to Slashdot.
Ripping an new rectum in the fabric of spacetime.
But most architecture just isn't that sensitive to weight. For example, steel frame houses have significant earthquake resistance and are just more durable overall. Most bridges cover modest spans and can continue to be steel and concrete. Further one has to consider the problem of wind force. If your structure is very light for its surface area, then it'll experience increased jostling due to wind. Then you need to engineer some sort of means for stabalizing the structure, maybe guy ropes or some sort of internal computer-controlled weight that counters these motions.
this may be a podcast
a sticspaceships/audio/story.mp3
:)
feed://science.nasa.gov/podcast.xml
but this is not:
http://science.nasa.gov/headlines/y2005/images/pl
smartass..
For those of you who are too young, that's a direct quote from "The Graduate". Family friend was telling the main character that plastics were the next big thing, the next big growth industry, the place to make your fortune.
Since then, the magic word has cycled through "Computers", "The Internet", and is currently "Biotechnology".
Why in Bush's name are we cutting fuding to nasa?
Erm, where did you get that info from? Bush does many shitty things, but cutting NASA funding isn't one of them. In fact, NASA is one of the few non-defense government agencies which has actually seen funding increases. Bush even threatened to veto a huge appropriations bill unless legislators increased NASA's funding by a billion dollars.
The official info on NASA's budget can be seen here.
Mars atmospheric entry won't be as big a heat problem as earth entry, because of how thin the atmosphere there is. If the plastic was resistant enough for that (which it's still probably not) then they could simply re-enter earth in something else, and leave the spacecraft in orbit, ready for another mission perhaps.
The standard for testing whether steels are brittle at low temperatures that we use today was known about and insisted upon by Lloyds of London in the 1930s - it was just taking shortcuts and a two year refusal to acknowledge that there was a problem that resulted in so many of the "liberty" and "victory" ships having problems. Some ships developed major cracks but were kept afloat - since the crack started at hatch corners on deck. One ship used in Antarctic waters in the 1950s developed a crack that opened up to well over a foot across each time the ship went over a large wave in a storm. The ship made it back to port when the crew drilled holes in the deck and bolted steel beams over the crack to hold the deck together. Since these were welded ships they were effectiveley one peice of metal, so a crack starting on deck could go all of the way around to the keel, which is why some of the ships broke completely in half.
Having square sharp cornered windows did the same thing with the Comet airliner - they also failed due to metal fatigue starting from a stress concentration. In the case of the airliner the fatigue properties of Aluminium (yes, americans spell it differently) were not considered to be important enough in the design process.
Back to polyethelene - the effects of radiation on this material are very well known. Despite years of research the best material for some parts of artificial knee joints remains the polyethelene exposed to radiation to produce more cross-links that was developed in the 1950s.
water is a wonderful radiation shield, borate it and it gets even better, I'd never walk by any spent fuel pool without it!
I understand one of the disadvantages composite materials have, besides the fact that they cost more and are generally harder to work with, is that their aging and failure modes are hard to predict. If you build airplane or spaceship parts out of metal, you can do small-scale short-time testing of the material and accurately predict the lifetime of the part, its probable failure mode, how its properties will decline as it ages, and the warning signs of imminent failure.
This is not true for composites. Accurate theory to scale up small and short tests to the full design lifetime does not yet exist. Furthermore, composites tend to fail all at once, without warning, and sometimes in response to stresses that previously they easily withstood.
Recall the RSS panels on the Space Shuttle, which failed in Columbia and in the CAIB test under surprisingly small impacts. This is not, I think, because the original engineers had their heads up their asses and didn't design for an impact with a bird or some such. I suspect it's because these composite parts are now 25 years old, and subtle changes due to aging have ruined their original design impact resistance, and have opened up unsuspected new failure modes.
In other words, one of the big virtues of metals is that they are much simpler materials, and the ability to predict the performance of your material accurately is a nontrivial criterion in selecting it.
While plastics are incredibly useful and durable .. from a chemical point of view... I'm much less likely to trust them in terms of long term stability.
I've seen these things dissolve in the slightest bit of an organic solvent (e.g. Dichloromethane or acetone)... and seen them melt with a souped up hairdryer (heatgun) at less than 200 degrees C. I wouldnt feel particularly safe with these materials shielding me from one of the harsher environs known to man (space).
Maby it's just my experience of seeing these substances take damage a lot, but i'd be real uneasy to trust my life to them over a bar of aluminum, which you can easily dip in water/organic solvents and heat to rediculous heats without so much as loosing it's bright metallic glint, let alone the all important structural integretiy.
If they're going to use plastics as a main part of the airframe, they're definately going to have to do some shielding from heat/radiation (U.V. light by itself can be quite destructive to certain plastics).
Neutrons are the bad boys. They don't have a charge like protons (alphas) and electrons (beta) so they aren't easy to stop. What makes them nasty is that they are massive and can do some real damage.
Poly (and water) make the best neutron radiation sheilding because it has alot of hydrogen atoms (one proton nuclei) which when hit with a loose neutron, will cause the neutron to loose 1/2 it's energy (two equal mass objects remember). So after a few collisions with a few Hydrogen nuclei (protons), the Neutrons become slow enough to be absorbed into any handy atom's nucleus (hopefully NOT in your DNA)
THAT's why they use Poly sheilding in space craft.
Your thin skin doesn't make me a troll
So this stuff is a fabric, so the implausible tensile strength numbers are probably for the individual fibers, not for a solid piece of the material. (The photo has him holding a "brick" of the material though.) Spider silk is as strong as high strength steel, and is very tough, but no one is suggesting building spaceships out of it. 2.6 times less dense than aluminum gives it about a density of 1, which is what polyethylenes typically are.
So they've managed to build a tough fibrous material. That's good, and it might make for a good micrometorite shield, and possibly a radiation shield. But it's not going to be a replacement for steel, titanium, or aluminum.
The radiation safety field has been using plexiglass (polymethylmethacrylate) as shielding against high energy beta particles for decades so its not very surprising that another polymer of a similar type can be used to shield against intrastellar particles of a similar type. The thing to understand is that although they liken the structure to that of a garbage bag, the higher the energy of the particle, the thicker the material needs to be and since those particles have very high energy in space, it is likely you are going to have a ten foot thick garbage bag as your shielding in future space ships...
...and it should be known by now
It's an allusion to http://www.imdb.com/title/tt0061722/ (The Graduate).
If you haven't seen the movie, shame on you.