You are not logged in.
Some useful Science Information in the current Scientific American, What a concept. And you get the usual Monthly fix of "MAN DESTROYS NATURE"
article too. I mostly buy Discover now, because atleast it doensn't pretend
to be a deep thinking pure science mag.
Cosmic rays. Fast moving Protons, (near Speed C) Tremedous ambilty
to penetrate flesh and and destroy DNA Strands. In an 18 month
trip withou protection, 1/3 of your body would be riddled with those
cuts. Not sure if body can repair damage. Daily Dosage of
80 REM in Deep Space.
Basically they Think It's a show stopper for Long Duration Trans Earth
Space Voyages. They are Hoping...err think, that it will stop a Mars Program.
Until somebody figures out a practical Solution.
They Talk about some attempts at theoretical solutions. Among them.
Super Ionize the Hull, to repell Protons, Wont Work
Magnetic Field to Deflect Protons, anybody have a 20 Telsa Magnetic coil??
And the really shocking part, If you use water as shielding, you need a water
jacket 15 FEET thick to fully protect a human being. To protect a crew cabin
of a cylinder Of Radius 30ft & Height 30ft, why you need, 202,000+ Cu Ft of Water. How much does that weigh???. 835 tons. This is probably 10x the mass of the crew cabin itself.
So maybe we do need a battlestar galatica approach, or much faster transit times. I think their numbers are overkill. They want ZERO emissions
for their protective water jacket and that's not neccessary.
I think a combo of 6 Ft Water & 1/2 foot graphite will do the job nicely, For
mars trip that is.
Offline
Ah yes, leave Mars to the robots, and lets use the money for human missions for (insert pet welfare money pit here).
But anyway... how much radiation is really dangerous though? The "E" in 80REM stands for "equivilent," and who calculated this statistic? The "oh no, radiation!" alarmist anti-scientists?
How about a combination of magnetic field generation and a thinner layer of water? Or how about polymer doped with boron or extra hydrogen gas? The crews' "bunks" might also be inside a smaller secondary shield to protect them better while sleeping to limit their overall dose.
NASA is also looking at twelve months in space, not eighteen, for a round trip to and from Mars. On the surface, you are fairly well protected by the Martian atmosphere. Put some dirt on top of the HAB, and the surface dose should be quite small.
Any talk of feet of water or whatnot is right out, if this is nessesarry, then we aren't ever going to get to Mars at this rate.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
An interplanetary craft doesn't need to look like a rocket - wrap your fuel tank around your living quarters!
Offline
Actually, yes it does need to look like a rocket (pointy) if it is to aerobrake without being too wide to fit on a rocket.
Also, most of the fuel needed for the mission will be burned getting out of Earth or Mars orbit, so you won't have much fuel to shield you either.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
Is water really the best shielding Liquid substance by weight??
What about a really viscous fluid like Petroleum. I have actually
tried to plunge a 3 inch rod into a vat. (La Brea Tar Pits) it takes real effort,
It sure seems to me that a 1 foot thick layer if that stuff would absorb an awfull lot of kinetic energy.
But If you want to get sillier you could use Honey.
However after a long while the Carbon bond breaking would result
in a inedible mix of Sugars + Methane + Etane + butane.
Which drives to the second point, wont some food stores become unedible
(or lose all nutritional value) eventually due to cosmic ray damage? I would think so.
Offline
The best material by weight would obviously be a polymer: made with light weight carbon and hydrogen as well as being a relativly thick but flexible solid. Hydrogen makes the best radiation shielding because there are no secondary radiation releases by spallation. The polymer (probobly polyethylene) might also be doped with boron or hydrogen gas impregnated into it, which would be even better.
Nothing thick or gluey would be thick enough to resist micrometeor impacts, and small molecules (petrolium, sugars) would break down more readily from radiation exposure.
Food should not be substantially affected, as long as the astronauts maintain a high intake of antioxidants, which they will do anyway. There are too many food molecules for the radiation to destroy, which is unlike a living cell where damage to one molecule can interrupt its function. Food cells, being dead, aren't going to be damaged unless absorbing a massive dose.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
I read the discover article too, and it did say that hydrogen is the absolute best for stopping them, but it also mentioned that a magnetic field could stop them. granted it would have to be a large superconducting magnet, but would this be so hard to do in space? it seems to me that as long as you kept it in the shade and cooled it down with helium it would stay pretty lightweight. Granted it's going to weigh something, but would it be possible for it to double as a mag sail or something? The electronics for the ship could be magnetically shielded.
Ad astra per aspera!
Offline
The electronics used in geostationary communication satellites are outside the protective Van Allen belt, and their electronics seem to work well enough with only modest shielding.
The trouble with a magnet is making one strong enough to signifigantly deflect near-C speed particles in only a few inches. Probably easier to add more passive shielding then it would to use an active magnet.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
hum, yes I was talking about shielding the electronics from the massive magnetic field, but maybe this wouldn't be needed. In the article they were talking about a mini magnetosphere, it didn't say anything about the need for it to activly deflect them that I can remember, just a pasive field... but I could be wrong.
Ad astra per aspera!
Offline
First I'm going to have to call the major statistic of the study bogus. 80 REM/day (or about .8 Sievert/day) is enough for serious signs of radiations sickness to become evident, with the possiblitie of some fatalities, of course this didn't happen to Apollo. In addition we have sent several missions (and countless probes) out beyond the Van Allen belts into "deep space" and the results of the cosmic radiation don't match these figures either.
Apollo measured cosmic radiation rates of ~1mREM/hr or .024REM/day. Even taking into acount that high energy protons are more ionizing then photons (a factor of 5 in Sievert calculations), we are still only talking about .12REM/day or 1.2mSv/day (mSv=millisivert). This is considerably higher then the average dose you would get on Earth (2.4mSv/year or ~.0066mSv/day), but hardly show stopping.
Indeed, their are lots of areas on Earth where you get a much higher daily radiation dose due either to natural radioactive deposits (like Brazil), high altitude (Denver), or a combination of both. In fact, in the US due to the greater quantites of radioactive deposits, airline travel, and X-rays, the average is higher, some 3.6mSv/yr. In fact, people in Ramsar, Iran recive nearly 260mSv/yr or .71mSv/day without adverse effect. Indeed their have even been some study linking low-levels of radiation with decreased cancer risk, persumably because of increased excersize of the body's self-repair mechanisims.
Without reading the study in question, it's hard to comment on their specific concurns, but in general I think this is a red herring. The US's experience in space shows cosmic radiation to be a minimal hazard to astronaughts, with some minor impacts on their long term health (a few percentage points more risk of cancer). Not something to be dismised, but not a show-stopper either. The plastic vests and better protected sleeping quaters some have talked about should make a signifigant dent in the radiation explorers would have to face.
He who refuses to do arithmetic is doomed to talk nonsense.
Offline
Protons aren't the only problem, despite there being lots of them and fast moving, the Apollo capsule's aluminum hull blocked a majority fraction of them, but Ritt didn't give the full picture and left out the real beasties: high-energy cosmic rays in the form of polynucleon ions. Nuclear fusion "events" and various stellar explosions. These are basically free atoms from Helium to Iron with the electrons stripped off and universally have extremely high speed. They have considerably more penitration and ionizing potential than even near-C protons and could be an issue for missions to Mars and beyond.
The danger from this particular type of radiation is a little different then plain old proton radiation since when a heavy ion hits shielding it creates a cascade of lighter particles by spallation, the effect becomming worse the higher the atomic number of shielding. Its actual effects are not that well understood.
"Heavy" cosmic rays might have a synergistic effect with exposure to low gravity too; it is now believed that people get several cancers normally throughout their lifetimes, but the immune system recognizes almost all of them and destroys the runaway cells before they can become a problem. Some tests on astronauts show that zero-gravity supresses the immune system, which might have a multiplying effect on cancer risk.
There is also anecdotal evidence that relatively small doses cause cataracts in the eyes.
I bet though that this problem is manageable; shielding can stop most of these nasty ions without adding too much mass, and exposure would be limited on the Moon (buried habitat, Moon itself blocking half) and Mars ("deep" atmosphere catches spalled particles). Astronauts could also be dosed with immune boosters, antioxidants, or advanced chemotheraphy drugs to reduce the effect, and perhaps even replace their corneas with advanced polymers that can't be harmed by radiation.
All else failing, we'll just have to get there quicker, and an advanced nuclear propulsion system developed.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
Protons aren't the only problem, despite there being lots of them and fast moving, the Apollo capsule's aluminum hull blocked a majority fraction of them, but Ritt didn't give the full picture and left out the real beasties: high-energy cosmic rays in the form of polynucleon ions. Nuclear fusion "events" and various stellar explosions. These are basically free atoms from Helium to Iron with the electrons stripped off and universally have extremely high speed. They have considerably more penitration and ionizing potential than even near-C protons and could be an issue for missions to Mars and beyond.
The danger from this particular type of radiation is a little different then plain old proton radiation since when a heavy ion hits shielding it creates a cascade of lighter particles by spallation, the effect becomming worse the higher the atomic number of shielding. Its actual effects are not that well understood.
There are ways for acounting for this. For some time now the scientific community has been arguing and trying to get people to use Sieverts instead of rem (Röntgen equivalent man). Sieverts generaly take into acount the greater ionizing power of protons, neutrons, and other heavy atomic particles in their calcuation of the equivlent radiation dose. In my calculation above I used the appropriet Sieverts for the situation, assuming all of the cosmic radiation was highly entergetic protons, giving a much higher effective radiation dose. This is fairly optimistic because not all cosmic radiation IS highly energetic protons.
As for the danger of heavy nuclei, this is more than balanced by their increased rarity. Sure high energy alpha particles and even heavier nuclei are much more ionizing than photons or protons maybe 100x more even. But they are FAR more rare, >1000x times rarer. Also, the heavier the ion, the more effective shielding is at stoping it generaly.
"Heavy" cosmic rays might have a synergistic effect with exposure to low gravity too; it is now believed that people get several cancers normally throughout their lifetimes, but the immune system recognizes almost all of them and destroys the runaway cells before they can become a problem. Some tests on astronauts show that zero-gravity supresses the immune system, which might have a multiplying effect on cancer risk.
There is also anecdotal evidence that relatively small doses cause cataracts in the eyes.
While the increased chance of cancer a Mars trip might result in is not negligable, the chance that it will manfest itself during the trip is. If we pick young, healthy people to be our explorers, the chance of their developing cancer during the trip is simply negligable. Heart attacks should be a greater worry for us. Cancer takes quite a while to develop into something life threatening anyways, even if exposure to 0g instantly caused one to occur.
I bet though that this problem is manageable; shielding can stop most of these nasty ions without adding too much mass, and exposure would be limited on the Moon (buried habitat, Moon itself blocking half) and Mars ("deep" atmosphere catches spalled particles). Astronauts could also be dosed with immune boosters, antioxidants, or advanced chemotheraphy drugs to reduce the effect, and perhaps even replace their corneas with advanced polymers that can't be harmed by radiation.
All else failing, we'll just have to get there quicker, and an advanced nuclear propulsion system developed.
I think the radiation problem is much ado about nothing. Aside from solar flares (which are a worry) cosmic radiation has very little short term effect on the Mars trip. Our explorers aren't simply going to suddenly die of radiation poisioning or develope cancers everywhere during their trip. Now, they may face a increased chance of cancer in the remainder of their lives, but this chance is fairly small increase (maybe as much as 10%) and I bet there are many qualified applicants who would be willing to risk it. I know I would. When you look at the grand sceam of risk for a Mars trip, radiation (aside from solar flares), realy doesn't figure into it.
He who refuses to do arithmetic is doomed to talk nonsense.
Offline
I agree. The author of the Sci Am article are probably anti-human spaceflight hacks doing their dirt with their chosen facts.
Offline
Why is it that people push "Battlestar Galactica" missions anyway? Someone even wrote a whole book on a "Battlestar Galactica" mission. ever read Destination Mars by Alain Dupas?
If someone is not interested in manned Mars exploration, why would he waste his time writing a book about it? Do they think big expensive missions will actually be funded, and that they can skim some money off of these lucrative government contracts? Seems some people look for more inexpensive ways to go to Mars while others look for more expensive ways to get to Mars in hopes of not going. Do they realize, the more expensive they make something look, the less likely it is going to happen? I think sending a chimp to Mars might lay to rest any qualms about the safety of sending humans there.
And what's with these scientists that don't want to send people into space? NASA's budget is a very small part of government expenditures. If public interest is space waxes and wanes, then so too will NASA's budget accordingly. People who want to probe the planets but never go there, I call "Do not touch" astronomers, they are very interested in astronomical objects, but they don't want too much public enthusiasm. If people actually go to these places, then space science will have more to do with everyday peoples lives, but the "do not touch" astronomers want to keep Space Science as an esoteric branch of physics that only they understand or are interested in.
Offline