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."

Comments

Re:Not a Podcast!

[flowerp]

RSS URL is feed://science.nasa.gov/podcast.xml, smartass

I am subscribed with the iPodder app. Again, how is this not a podcast?

Re:Nature's way...

[khallow]

I don't think so. Metals still have a series of characteristics that aren't matched by plastics and advanced fibres. For example, steel is much harder than plastics (or the resin portion of carbon fibre), chemically compatible with concrete (another unfashionable material that isn't going away), handles compression loads well, easy to work with and machine, cheaper (IMHO), and recyclable. Things that handle significant localized forces like most screws or nuts, probably will remain metal. Weight critical applications (cars and spacecraft) will probably eliminate most uses of metals.

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.

Re:Nasa

[FleaPlus]

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.

Re:Outgassing and thermal properties

[dbIII]

Liberty ship hulls in cold North Atlantic waters (learning that some steel alloys are brittle in low temperatures)

Incorrect - that was well known before the Liberty ships were constructed but since it was wartime a lot of corners were cut in the design and construction. The Liberty ships are a good example because there were so many of them of similar design (4694) and so many that developed major cracks (1289) so we have plenty of information about what happened. The two major problems were the use of steel that normally wouldn't be used for low temperature service (hit it with a hammer at 0 C and it will crack very easily), and designs developed for riveted ships being applied to welded constuction without modification. Square sharp cornered hatches provided a point where stress was concentrated and cracks could start easily. One of the T-2 tankers, the Schenectady, actually cracked completely in half in the fitting out dock one night before the ship had even been launched. If you can track down the book "The Brittle Fracture of Steel - W.D.Biggs 1960" or "Brittle Structure of Engineering Structures - E.R.Parker 1957" there is plenty on these, newer texts typically just include a couple of photos and a couple of lines of text.

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.

Here's the important part of the article

[eaolson]

The article several paragraphs says,

RXF1 is remarkably strong and light: it has 3 times the tensile strength of aluminum, yet is 2.6 times lighter -- impressive even by aerospace standards.

"Since it is a ballistic shield, it also deflects micrometeorites," says Kaul, who had previously worked with similar materials in developing helicopter armor. "Since it's a fabric, it can be draped around molds and shaped into specific spacecraft components."

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.