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."
there was a recent bbc program about a Solar system tour mission where a magnetic shield was generated aournd the ship. A crew member still died from cancer after getting too much radiation.
Space Odyssey: Voyage To The Planets
Quite a good show actually.
http://www.bbc.co.uk/pressoffice/pressreleases/stories/2004/10_october/13/space.shtml
High energy gammas, electrons, and charged particles give off bremsstrahlung radiation when they are stopped- this means that you approach diminishing returns as you apply shielding against space radiation. Using twice the lead does not result in twice the shielding.
When you get away from Earth and you don't have Earth itself blocking half your sky and the mag field providing some geomagnetic shielding, space radiation levels go up. You don't have trapped protons, but you have more higher energy stuff.
This pushes you up against weight limits quickly. I'd imagine that you'd need many launches to assemble your Mars ship in orbit, with the living quarters inside a half-inch steel,aluminum, and lead case, surrounded by a foot of water (you recycle the water all the time to live off it).
There are solutions, but they are much more complex than the Apollo tin can or Ti-Al-ceramic of the Shuttle.
My first take of magnetic shielding is to think of Earth- our mag field funnels particles into the poles and traps e and p in the van Allen belts. A big coil around your ship would funnel particles too, and would not touch galactic cosmics because they are too energetic.
http://radiationshielding.nasa.gov/transport_calc1.html
Go to the above link, click on "go to transport calculations"- there is a quick and dirty calculator that allows you to see how shielding effectiveness drops off with increasing particle energy. The calculator uses an orbital particle flux that was measured during a flare. The thickness of your shield is not in inches, it's in g/cm2, so all elements are normalized to density.
Um, maybe we could HIRE the arabs and the chinese to do the space work FOR us (in our equipment, under our control, kinda like coolies(!)) - an unlimited supply of the li'l buggers when the rads start totaling-up.
IIRC, what you're protecting yourself against are sub atomic particles, maybe a neutron is the largest. What you're trying
to do is to create a dense layer of atomics, preferable, only protons, to block the particles. Otherwise, regardless of
the relative speeds, the invading particle slips between the space between the atoms in the shielding.
Speed won't matter if there's nothing there to stop it on it's way to smacking into DNA molecules.
I wear a foil hat around the house for just that reason. No cancer here.
What's the temp in space out of direct sun light? Cold enough to support a super conductor generated magnetic field around a space craft? I think so! ;-)
Create a spacecraft that emulates the planet Earth by creating a large electromagnetic field that would act to deflect this radiation away from the crew compartment and other sensitive areas.
You know, I wonder whether running a magnetic field around the ship would serve to sheild the crew the way the earth's magnetic field sheilds us--and how much power would be needed to create an effective sheild.
Cosmic rays are high energy photons. "Light" of a higher frequency (and hence more energetic) than X-ray.
I forgot to mention- for your target element I'd pick Carbon, because tht's what we are made of other than water.
I ran the transport with a Gold shield at 10 g/cm2 (a 4x4 inch piece of shield would weigh about 2 1/4 pounds) and you can see that at low E, you get orders of magnitude of shielding. At 100 MeV/nucleon you get roughly a factor of 100. From 200MeV/nucleon out, though, very little shielding is seen. Even a thick gold shield does not stop much of the high energy particles.
Anyhow the calculator is fun to play with.
For a real serious particle transport tool look at
www.srim.org
They all have the speed of light. But when one is flying into them, they are blue-shifted and more energetic.
Cosmic rays are high energy photons.
Cosmic rays are mostly atomic nuclei stripped of electrons and zooming along at very very high energies.
There are some photons, they've measured some really energetic ones, but for your garden variety cosmic think of a silicon or iron nucleus.
Correct. But the energy is different based on the (perceived/experienced) wavelength.
"Cosmic rays are high energy photons. "
Oops, meant to put your comment in quotes, makes more sense that way.
BTW since they are not photons but particles with mass, different inertial frames will see them with different velocities. Even the really energetic ones don't get that cloce to c.
I like the way you think. {grin}
"You cannot possible believe this is something they just noticed ? "
See my post 82, it has links to NASA radiation shielding and space radiation stuff.
They worked out lots of these issues for Apollo, way back when we had manned lunar capability.
Are you CRAZY?!?!????? LEAD is POISON!!!!! You can't use lead for a shield. That is verboten by OSHA. Next thing you'll be suggesting asbestos for a heat shield. Ha! Where have YOU been for the last 15 years?
Big OOPS from me. You're right. Cosmic rays are not massless as photons are.
Aargh, propulsion is the key, not shielding, if you decrease the transit times, you decrease the radiation hazzard.
If we had something like Orion, we could get to Mars in a month or two and we could layer the ship with considerable greater shielding as well as reducing the radiation hazzard inherent in long transit times.
All this article does is remind one of why chemical rockets are not a good technology for transport further than the moon. We really shouldn't plan on 3 year Mars missions in the future, but 3 month Mars missions will work.
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