Posted on 08/01/2005 1:19:26 PM PDT by LibWhacker
The radiation encountered on a journey to Mars and back could well kill space travellers, experts have warned. Astronauts would be bombarded by so much cosmic radiation that one in 10 of them could die from cancer.
The crew of any mission to Mars would also suffer increased risks of eye cataracts, loss of fertility and genetic defects in their children, according to a study by the US Federal Aviation Administration (FAA).
Cosmic rays, which come from outer space and solar flares, are now regarded as a potential limiting factor for space travel. "I do not see how the problem of this hostile radiation environment can be easily overcome in the future," says Keran O'Brien, a space physicist from Northern Arizona University, US.
"A massive spacecraft built on the moon might possibly be constructed so that the shielding would reduce the radiation hazard," he told New Scientist. But even so he reckons that humans will be unable to travel more than 75 million kilometres (47 million miles) on a space mission – about half the distance from the Earth to the Sun. This allowance might get them to Mars or Venus, but not to Jupiter or Saturn.
Risky business
Helped by O'Brien, the FAA's Civil Aerospace Medical Institute in Oklahoma City investigated the radiation doses likely to be received by people on a 2.7-year return trip to Mars, including a stay of more than a year on the planet. The study estimated that individual doses would end up being very high, at 2.26 sieverts.
This is enough to give 10% of men and 17% of women aged between 25 and
34 lethal cancers later in their lives, it concludes. The risks are much higher than the 3% maximum recommended for astronauts throughout their careers by the US National Council on Radiation Protection and Measurements.
The risks are smaller for older people because cancers have less time to develop. But women are always in more danger than men because they live longer and are more susceptible to breast and ovarian cancers.
The study warns that cosmic rays would also increase the risk of cataracts clouding the eyes. Furthermore, men exposed to a solar flare might suffer a temporary reduction in fertility, and the chances that any children conceived by travellers to Mars will have genetic defects are put at around 1%.
Serious brain damage
The study's lead author, the FAA's Wallace Friedberg, highlights other work suggesting that heavy nuclei in cosmic radiation cause "serious brain damage" in mice, leading to memory loss. "Heavy nuclei exposure must be a serious consideration for space missions such as a trip to Mars," he says.
Improving spaceships' shielding by using water, hydrogen or plastics can protect astronauts to some extent. But this is limited by the constrictions of craft weight and design, Friedberg points out.
"Increased speed would also reduce radiation exposure" by reducing journey times, he notes. "And drugs or food supplements that can reverse radiation damage are being considered."
Others suggest more radical solutions might be needed. "Radiation exposure is certainly one of the major problems facing future interplanetary space travellers," says Murdoch Baxter, founding editor of the Journal of Environmental Radioactivity. "Unless we can develop instantaneous time and space transfer technologies like Dr Who’s TARDIS."
That is true.
But wouldn't the higher energy "blue" cosmic rays be offset by their lower energy "red" counterparts (the ones you are running away from) with it all averaging out to same thing you would see at zero velocity. This would depend on the source of course. I'm assuming uniformity in three dimensions. You may be talking about cosmic rays from the sun or some known source. Well that would be different. In that case I would agree with you.
It still seems to me that if the source of the cosmic rays is not known and the incoming rays are independent of angle then you should not be able to make any measurement on these rays that would tell you anything about your velocity. If the energy of the rays in the forward direction is higher than the rays coming in from your rear then a measurement of this energy would tell you what your absolute velocity is. Except that there is no absolute velocity. Of course if you knew the source of the cosmic rays then you could obviously make a measurement of your relative velocity with respect to that source.
This relativity stuff is really difficult.
I mistated the nature of cosmic rays. They are not massless photons, they are particles.
So at that, a person in space is more exposed than a person under the blankets of magnetism and atmosphere that cover earth. I suspect velocity relative to earth is an inconsequential variable in calculating exposure to cosmic radiation.
They didn't speak with one voice on everything. One thing they were in agreement on was that American goods were cheap and high-quality and that America had excellent prospects for international competition in trade and commerce. Another was that land was cheap and plentiful.
They might well agree that the situation today is very different and wonder what has gone wrong. Family farms nearly disappeared, houses for $1/4 million, Japan and China putting tariffs on American goods to the point where Americans would be at all concerned? Somehow this ship of state has flipped over in the river.
> you can shield a small portion of the spaceship with enough lead to create a safe environment.
Yes. Emphasis on "small." But there are better things to shield said compartment with than lead... water, food, structural elements, computers, etc. Lead is otherwise just dead weight.
> According to Robert Zubrin
While he is correct in this case... take everything that man says with a grain of salt the size of your head.
So how come most of the larger life forms on this planet inconveniently (for this theory) fail to die off during periodic reversals of the Earth's magnetic field?
If they build a heavy ship and use it over and over the excess weight of shielding wouldn't be such a concern. They will probably want several so the mail service to Mars would have some regularity. Space Shuttles, the real kind.
Try building a power plant....its water right in the line after sulphur dioxide....
You could use the water once there as well and generate H.
I think you need to read up a little. According to your example, if you hit a person head on walking 2 mph toward you, he wouldn't be hurt (from the car's reference frame).
No. You're misreading what I'm saying. I think cosmic rays are really just various particles and they hurt when they hit you. My argument was basically that if they are coming at you from all directions and you don't know what the source is then speeding up doesn't make them hurt any worse. This follows from the fact that the field of cosmic rays should look the same to you if you are traveling at 2 MPH or 2,000,000 MPH. If if didn't then you would know something about your velocity relative to the cosmic ray field. Assuming it is really uniform then I don't think you could do that.
But I could be wrong.
Where is Dr. Stochastic when we really need him?
How Do You Add Velocities in Special Relativity?
Suppose an object A is moving with a velocity v relative to an object B and B is moving with a velocity u (in the same direction) relative to an object C. What is the velocity of A relative to C?
In non-relativistic mechanics the velocities are simply added and the answer is that A is moving with a velocity w = u+v relative to C. But in special relativity the velocities must be combined using the formula
w = (u + v)/(1 + uv/c2)
If u and v are both small compared to the speed of light c, then the answer is approximately the same as the non-relativistic theory. In the limit where u is equal to c (because C is a massless particle moving to the left at the speed of light), the sum gives c. This confirms that anything going at the speed of light does so in all reference frames.
This change in the velocity addition formula is not due to making measurements without taking into account time it takes light to travel or the Doppler effect. It is what is observed after such effects have been accounted for and is an effect of special relativity which cannot be accounted for with Newtonian mechanics.
The formula can also be applied to velocities in opposite directions by simply changing signs of velocity values or by rearranging the formula and solving for v. In other words, If B is moving with velocity u relative to C and A is moving with velocity w relative to C then the velocity of A relative to B is given by,
v = (w - u)/(1 - wu/c2)
Except the relationship is not linear. The more acute the dose, the more the severe the harm as the body can repair most of the damage if the dose is acquired chronically.
We conveniently have 15 pounds per square inch of shielding overhead. That's a lot, see my earlier post with the links to the shielding calculator.
People have tried to line up mass extinction events to geo reversals- it matches some but not all. Sea level radiation would go up, but nothing really drastic as to cause an extinction event.
I watched a program about the space race today. How the Russians was way ahead at first with sending the first man to space and the first space walk. They lost the the race to the moon to the Americans.
After the cold war there have not been that much money put into space activity in the US. Partly because of the cost, military expenses like in Iraq and the budget deficits.
Thats why I really think the Chinese will get the first man on Mars. They have a lot of smart scientist and they have probably almost caught up to the US. Plus their government have much more power over the national spending and therefor dont need to please the citizens in the same way as in the US. So I have a feeling we have to wait for the Chinese to make that trip to Mars.
Doing a few calculations in my head, he says you can expect to get 2.26 Sieverts in a 2.7 year mission. That works out to be 226Rem at about 84R/year. To get to the NRC maximum dose allowed to radiation workers of 5R/year based on a 40 hour work week (of course it will be a 168 hour 7X24 hour job, so your allowed exposure is just over 1R/year), you would need a lead coating of almost 4 inches thick.
See my post 82 for a link to a transport calculator that will let you see how much lead you need.
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