beastin ([info]beastin) wrote,
@ 2007-12-30 15:31:00
Previous Entry  Add to memories!  Tell a Friend!  Next Entry
Transit, radiation, and Mars
Today I dug up some good news and bad news for prospective Martian tourists and colonists. Mainly I looked up radiation, but I've included some other fun facts below.

First, the good news. From what I can tell, solar flares do not seem to be as much of a problem for interplanetary travel as they have been portrayed. According to a NASA article, http://science.nasa.gov/headlines/y2005/07oct_afraid.htm, solar radiation is adequately shielded by standard hull materials for spacecraft. Even a sizable flare should only result in moderate radiation sickness for the occupants of a spaceship with the 10 to 11 g/cm^2 of shielding used in current short-range craft, http://www.nasa.gov/mission_pages/stereo/news/stereo_astronauts.html, http://en.wikipedia.org/wiki/Radiation_poisoning. In fact, it may be a good idea to plan trips during maxima of solar activity since increased solar particle radiation deflects galactic radiation, which is much more difficult to shield against.

Now for some bad news. A round-trip to Mars is estimated by Robert Brit at Space.com, http://www.space.com/scienceastronomy/mars_dangers_040120.html, to entail (presumably for current spaceship hulls) something like 60 rem of radiation (1 sievert = 1 Sv = 100 rem). According to http://www.nasaexplores.com/show_912_student_st.php?id=04032381148, the monthly, yearly, and lifetime radiation dosages for astronauts considered acceptable by NASA are 25 rem, 50 rem, and 100-400 rem (lifetime numbers depend on your age and sex). Moreover, he claims that each year on the surface of Mars you can expect to soak up on the order of 30 rem. Thus, if you decide to stick around (above ground), you can expect to exceed NASA's lifetime radiation allowance within about a decade.

In addition to abundant particle radiation, Mars sports an atmosphere consisting of 95% carbon dioxide with a pressure of less than 1 KPa (c.f. earth's sea-level pressure of 101 kPa and the 30 kPa pressure on top of the Himalayas), http://en.wikipedia.org/wiki/Mars_(planet). Finally, while Mars receives only 44% percent as much light as the earth, its thin atmosphere ensures an amount of UVB electromagnetic radiation exceeding that of earth, http://mpfwww.jpl.nasa.gov/mgs/sci/fifthconf99/6128.pdf,
http://findarticles.com/p/articles/mi_qa3931/is_200301/ai_n9171725.

Oh, and the temperature? It ranges from −140 °C during the polar winters to highs of up to 20 °C.

(Post a new comment)


[info]dushai
2008-01-02 06:58 am UTC (link)
Short-term options: Wear suits with shielding for the trip; alternatively, accept that the first Martian tourists and colonists will be daredevils who just have to deal with potential radiation poisoning along with potential spacecraft malfunction and other potential disasters.

Medium-term options: Develop lighter shielding materials (perhaps {electric field}-based rather than physical?) and lighter spacecraft, allowing radiation-shielded voyages. Construct shielded buildings on Mars, so that colonists spend most of their hours less exposed.

Long-term options: Terraform Mars (or at least a large sealed bubble on Mars), introducing a nitrogen/oxygen atmosphere sizable enough to shield most of the radiation nasties.

Disclaimer: This isn't my field of expertise, and I'm just speculating wildly.

Why the interest? Are you planning a trip soon?

(Reply to this) (Thread)

[info]beastin
2008-01-03 04:27 am UTC (link)
Getting to and surviving on Mars is an ongoing interest of mine. Deep down, I think it's because I like the idea of a fresh start on a new world. It's also an interesting engineering problem and a good safety measure for insuring the continued existence of mankind. Not to mention my inherent wanderlust. :)

If you're inside a ship, it's better to put the shielding in the hull than to try to layer enough onto a guy in a suit. You could certainly add a bit more shielding to the hull, but the point of my post was that, even if you didn't, a solar flare would not kill people. It's not a show stopper.

Incidentally, it's also been pointed out that, since solar flares are intermittent, it would be enough to have a bunker on the ship to hide in, e.g. the space between your water tanks.

During my senior year of Caltech I did some calculations to determine the feasibility of a magnetic shield. The energy requirements are prohibitive unless you run the current through a superconductor. Using the best superconducting wire I could find online at the time I determined that you'd have to wrap the ship in a solenoid 20cm in diameter. Not easy, but doable. Probably not worth the trouble unless you're going farther than Mars, although it may be easier now.

Burying Martian buildings is, I think, an excellent idea. At very least, there's no reason to be soaking up radiation while you're asleep.

Googling I found the following:
Pressure at sea level: p_s = 10 N/cm^2
Density of air at sea level: d_s = .0012 g/cm^3
Equivalent shielding capacity of the earth's atmosphere: l_c = 3 m concrete
Density of concrete: d_c = 2.4 g/cm^3

Very roughly then, I'd guess that, at earth's-sea-level pressure you'd need:
p_s/g/d_s = 8.5 km
of air or, using the other data,
l_c*d_c/d_s = 6 km
of air. These numbers aren't very trustworthy, since, among other things, I'm assuming in the first case that the vast bulk of the earth's atmosphere experiences the same gravitational force, g = 9.8 m/s^2, (which should be approximately true) and in the second that the radiation stopping power of a material is strictly dependent on mass (which I know not to be true, but I also have no idea what the scaling factor is between air and concrete). At any rate, it seems like a bubble a couple of kilometers high would be necessary. That's a hell of an engineering project, and no small amount of air. On the other hand, the Valles Marineris is something like 8 km deep.

I love the idea of terraforming Mars. It's the best candidate that we've got in the solar system, and it's probably even feasible with current technology. The cost of a good terraforming job would be olympian, however, and I'm afraid that most of our effort (that is, the atmosphere) would bleed off over time. Admittedly, this bleed-off would not happen quickly.

Given that the radiation levels on Mars are not actually ridiculous, I tend to lean toward improved biology as the optimal long-term method of dealing with the problem.

In the short term, though, I think you hit precisely the mark with your daredevil comment. I'd be willing (and I'm sure I'm not alone) to accept a 1/20 chance of death to see Mars in person. NASA currently aims for a 1/1000 chance of death for astronauts. That seems overly conservative for a frontier. Of course, out of something like 1000 astronauts/cosmonauts (counting repeats) 19 have died, so the 1/1000 number should perhaps be taken with a grain of salt.

Count-disclaimer: This isn't anyone's field of expertise. We're all just speculating wildly.

(Reply to this) (Parent)

Create an Account
Forgot your login or password?
Login w/ OpenID
English • Español • Deutsch • Русский…