Slashdot Mirror
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."
It's close enough.. it's an audio file with the intent of being news listened to on a portable audio device in a timeshifted manner.
Only Slashdot pedantry would differentiate it from a podcast by the lack of an RSS feed. Secondly, there might actually be a feed somewhere that it's attatched to, but they're linking just to the specific article. This would still make it a podcast, just a single instance of the broadcast material.
This troll is old and worn out already.
There is no risk to you.
Nobody is asking you to go to Mars and it just so happens that some people still have the spirit of exploration and adventure and will volunteer to go knowing the dangers involved. (I know this to be true because I would raise my hand for the chance).
If America can't find someone to volunteer and do it for the spirit of exploration, China, a few years later will order someone to do it for prestige.
Ripping an new rectum in the fabric of spacetime.
So the best way is to kill the truth by stopping science. Also by attacking the credibility of the media. It's difficult for people to focus on an action to take when they're being confused by contradictory messages and you don't know which one to believe.
I wrote a journal article yesterday about why being pro-science is the most important message in winning the right wing extremist war on women. http://science.slashdot.org/~Safe%20Sex%20Goddess/ journal/
Abstinence is a government conspiracy. www.SafeSexZone.co
Initially, it'll be the same point as the original manned missions to the moon: Proving that we have a bigger collective dick that the Soviets / Chinese while happenning to also do some science on the side. After that, our government and NASA will return to their usual psychotically-risk-averse stupor.
We desperately need to get some competition going on in space exploration or nothing's going to get done. Come on China...
I'd want to see how the material handles long-term exposure to vacuum and large temperature swings before using it in any space-borne structural applications. Most plastics contain plasticizers that help improve flexibility and handling properties, but which slowly evaporate leaving the material brittle (anyone ever see what happens to a plastic milk jug left in the sun for a year?). Moreover, plastics tend to have structural properties that are very temperature sensitive -- at modestly high temperatures, plastics slowly stretch to failure, at modestly low temperatures, they fracture. The "temperature" in space is strongly dependent on whether the surface is facing the sun or not. It's baking hot on the sunny side and freezing cold on the shady side -- not a good environment for plastics.
The history of material science is the history of failures such as the catastrophic failure discovered in Liberty ship hulls in cold North Atlantic waters (learning that some steel alloys are brittle in low temperatures) to the Comet airplane crashes (learning that aluminum fatigues from repeat cycles of stress). I can only hope that NASA does something like LDEF with this material before depending on it to hold its properties for several years of space-exposure.
Two wrongs don't make a right, but three lefts do.
How is this even flamebait?! What the parent said is true. We would have never have sent a man to the moon if we were not in a technological superiority race with the Soviets. While I will admit that going to the moon is an AMAZING feat for humanity to marvel at for a long time into the future, the actual scientific value of such a mission when compared to its cost is greatly diminished.
That being said, we need to go somewhere other than earth orbit. If we keep going on into the future without looking at ways to live without earth we will be doomed to eventually perish here. The planet keeps getting smaller and smaller and the population keeps increasing. Eventually in the relatively near future we will either die en masse from starvation, lack of resources, etc, and (hopefully) leave some survivors, but we could easily become extinct as well. Technology is only going to help us now. If such a mass extinction of humans occurs they will have little fertile land to live off of and very few animals to hunt. We need to kick ourselves out of the womb before we as a race die like a stillborn fetus.
The mother can only sustain our greed for consumption of natural resources for so long.
zosxavius photography
Polyethylene is almost never transparent because it crystallizes very easily with its nice simple ...-CH2-CH2-CH2-... backbone. The resulting microcrystals scatter light and make the stuff milky. If you want transparent polymers, you use a backbone structure that doesn't easily form crystals, for example polystyrene, where the big benzene rings tend to jut randomly left or right out of the backbone.
I would guess that their new form of PE is a variant on long linear PE, with reduced branching of the CH2 backbone. This is going to have an even greater tendency to form crystals (Indeed, the crystals may be an essential part of the high strength feature, because they tie different PE chains together.) So I very much doubt it would be transparent.
No metal can ever be transparent, Star Trek IV notwithstanding, because to be a metal is to have free electrons, and free electrons absorb a broad spectrum of light. Put it another way: if you're a metal, you're a conductor, or equivalently an antenna, and that means you absorb electromagnetic radiation, i.e. light. So you can't be transparent.
Would you, perchance, have seen a study that actually for once addresses bremsstrahlung doses with more than a passing mention? Every time I see a study on radiation exposure for a Mars mission, after long detailed calculations on what would be needed to meet minimal health standards, there's usually a couple of lines to the effect of "These calculations do not include the effect of bremsstrahlung radiation, which can be expected to significantly increase the total radiation dosage." All of the studies I've seen use incredibly simplistic models (often a 1d radiation source impacting perpendicularly to a one or two layer shield).
GEANT is pretty good at this, and it's not hard to use. It would be easy for NASA or whoever to do some quick & dirty studies with it with some simple material model for what an interplanetary spacecraft might look like. If they haven't done this, they ought to.
And btw, I don't think it makes much sense to talk about 'bremsstrahlung doses'. Brem from a particle as energetic as a cosmic ray can easily have enough energy of its own to pair produce... and those particles in turn may also brem, etc.
This is called an electromagnetic cascade. And it doesn't necessarily start with a bremsstrahlung photon. Figure 2 in the fine article shows a hadronic part of a cosmic ray shower, which happens to include a pi0. The pi0 secondary has a very short life, and so will decay into two photons before it travels an appreciable distance. These photons will probably be energetic enough to produce the same kind of electromagnetic cascade that high energy bremsstrahlung would. This is why I personally would talk about doses due to electromagnetic showers in general, rather than bremsstrahlung. There is no logical separation.
Just in case you don't already know all this -- look at figure 27.17 on page 22 of this review article. This shows the expected amount of energy deposited for a shower caused by a (30 GeV) electron as a function of material depth. Of course the location of the maximum depends on the energy of the impinging particle.
So TFA is effectively saying: if the design of spaceships requires that astronauts have to sit to the left of the maximum for high energy cosmic rays, and if this is the main source of radiation for astronauts, then it would be good to move the astronauts as far left of the maximum as possible. I.e., use a material for the walls of the spacecraft that is thin in terms of radiation lengths.
To estimate the actual dose you expect the astronauts to get, then you need a reasonably detailed simulation. To accurately estimate the actual health effects is more difficult. But high energy cosmic rays are the main problem, then the basic optimizing principle is pretty clear.