September 16, 2009
Too Much Radiation For Humans In Mars Trip

Dreams of a human trip to Mars run up against limits to allowable human radiation exposure.

But calculations by Cucinotta and his colleagues suggest the trip would not meet NASA's existing rules, which aim to keep each astronaut's lifetime risk of fatal cancer from space radiation below 3 per cent.

For journeys outside Earth's magnetic field, astronauts could reach that limit in less than 200 days in a spacecraft with aluminium walls nearly 4 centimetres thick, according to worst-case scenario estimates (Radiation Measurements, DOI: 10.1016/j.radmeas.2006.03.011).

But a trip to Mars and back would take over 2 years. Two potential solutions:

  • Travel much faster.
  • Use several times the amount of mass as would otherwise be used.

Of course both of these approaches require far more energy. The faster trip is especially problematic because more energy would be available to launch a space ship toward Mars than to launch it back toward Earth. Getting a ship to move fast enough on the return trip would be a big challenge.

One way to get a ship to Mars that would have lots of chemical rocket mass to propel a return trip: Send two space ships. First send one slowly that would carry a lot of fuel. That fuel would enter Mars orbit before humans even left Earth. Then humans could leave Earth on a fast ship and arrive to find another fast ship with lots of fuel ready to take them back to Earth.

Part of the radiation exposure would come while humans are on Mars. How to reduce that exposure? Send robots ahead of time that would burrow down underground to create living quarters in several places that would be within driving distance of each other. The astronauts could move from underground shelter to underground shelter.

Of course, all this requires huge amounts of money and resources. Could other approaches work? I can imagine beam technology for pushing spaceships to faster speeds with power sources on stations in orbit around Earth and Mars.

What else? Think small. Methods to cure cancer or prevent cancer would reduce the scale of the problem. Nanobots could repair astronaut bodies as the damage occurred. Or nanobots could kill cancer. So we can wait 30-40 years to go to Mars until we have the biotechnology and nanotechnology sufficient to reduce the risks from higher radiation exposure.

I do not see the point of going to Mars with today's technology. Better to first push the edge of what is possible before sending humans on a trip that would put people on another planet for a pretty limited period of time. Humans went to the moon all we got were some cool videos.

Share |      Randall Parker, 2009 September 16 10:12 PM  Space Exploration


Comments
Kudzu Bob said at September 16, 2009 11:07 PM:

Hasn't there been talk that some sort of light-weight electromagnetic device might shield astronauts from cosmic rays?

Brett Bellmore said at September 17, 2009 4:28 AM:

Yes, artificial magnetospheres should do the trick, as well as having propulsion applications.

The problem with material shielding is that it creates cosmic ray secondaries; There's a wide range of thicknesses over which your radiation exposure *increases* as you add to the shielding. But with thin enough shielding to spare you the secondaries, a solar flare will leave you crispy. So material shielding has to be REALLY thick.

TheBigHenry said at September 17, 2009 5:19 AM:

Increase NASA's rules to 10%.

:-)

Engineer-Poet said at September 17, 2009 5:32 AM:

Brett captured the dilemma about shielding, I see.  Back in the 70's, the L5 folks calculated that about 4 feet of rock or slag was the minimum.  Artificial magnetospheres will get most solar flare stuff IIUC, but they aren't going to block high-energy protons.

The problem is the insistence upon ballistic trajectories.  Why?  We can build solar sails and ion drives.  The only thing we really need chemical rockets for is the initial kick to an escape trajectory to get through the Van Allen belts quickly.

pucca said at September 17, 2009 5:34 AM:

There has also been discussions about sending astronauts to Mars, but not returning them. I think that the primary rationale was to reduce the costs of the mission. If the astronauts will be living out their lives on Mars, an increased risk of cancer may be acceptable.

Thras said at September 17, 2009 6:45 AM:

What model are they using? If the lifetime risk was calculated back in the Linear No Threshold model days, then there may actually be far less to worry about from these doses.

danysdragons said at September 17, 2009 8:31 AM:

Even if the risk of cancer from the radiation is, say, double NASA's allowable limit of 3%, that would still be less than the risk from smoking cigarettes - a risk millions of people voluntarily take on every day.

Tom Billings said at September 17, 2009 8:50 AM:

Note that Mars, and even Mar's Moons, Phobos and Deimos, have what is needed to make propellant right there, if one is willing to do so, and build the vehicles involved to use Liquid Oxygen and Methane. Note that XCOR and several other companies are already building Methane/Oxygen engines. Using Propellant Depots on the Moons of Mars has been recommended by the Augustine Commission in its summaries released so far. Add to this a NOCHO strategy (No One Comes Home), and the productivity of each trip out to Mars goes up dramatically for each dollar spent. Since people already put 20+ years into some Space Astronomy/planetary geology programs like Hubble, this will not be completely without precedent. If needed, let them come home after 20 years, and a reconditioning regime for Earth gravity. Retain landers on the Martian surface for fast point-to-point travel on Mars, and for emergency evacuations to the Phobos Base if needed.

In longer stays on Mars the largest contributions to radiation exposure will be inside the settlement itself, so put the settlement in Martian lavatubes, and remove that radiation dose as a problem. For those staying up at the Phobos propellant depot/base, tunnel into Phobos for the raw materials needed for propellants, and live in the tunnels. For those who travel on the lunar surface, it will be possible to shield against flares with magnets using the new 242 degree Kelvin superconductors, which would need no refrigeration on Mars. The damage from cosmic ray protons would be ameliorated by making the walls of Mars buggies as thin as possible, since it is the secondaries produced by hitting insufficient intervening mass that cause the worst damage.

None of these problems are insoluble within the current technical base.

Regards,

Tom Billings

Allan said at September 17, 2009 9:26 AM:

For a faster trip, use nuclear propulsion. If we can revive Apollo for a moon trip, about reviving NERVA for pure space vehicle ... one that never lands.

Tom is correct, Mars has the ingredients to produce fuel for the return trip. Visit the Mars Society and read Bob Zubrin's plan.

kurt9 said at September 17, 2009 11:23 AM:

Common antioxidant supplements can radiation harden humans. The common food preservatives, BHT and BHA, in nano-vector form can certainly radiation harden humans, like 5000 times:

http://www.rice.edu/nationalmedia/news020808radiation.shtml

Any of you who are survivalist types should order up some BHT and BHA from the LEF website. It will make you more resistant to those dirty bomb attacks that the Muslims R Us crowd might try to pull on us.

If your a life extensionist, you're probably already radiation hardened to handle 4-5 times the amount of radiation of the average Joe Blow.

philw1776 said at September 17, 2009 12:58 PM:

The VASIMIR rocket with its high ISP could reduce crew trip times considerably.
Outbound, astros should sleep and spend much of the day in a crew quarters surrounded by fuel tanks as shielding. Tanks will be nearly empty on return trip though.
Prior robotic rockets can carry H2 and use in-situ Martian CO2 to make CH4 and O2 chemical fuels for return takeoff to rendesvous with the orbiting VASIMIR craft.
I'm confident that in a couple decades we'll have a far better nano-biological handle on how to deal with cell repair and damage from radiation.

David Govett said at September 17, 2009 4:15 PM:

Go at night.

Wolf-Dog said at September 17, 2009 7:40 PM:

If we have powerful nuclear propulsion, then it should not be difficult to add a 10 feet thick rock shield around the spacecraft (probably equivalent to 80 km of air). For instance, if the spacecraft is very big like the Titanic, then a 4 feet thick lead/rock wall would not be too much in comparison to the size of the Ship.

By the way, the idea of artificial magnetosphere was covered in Robert Heinlein's book "Orphans of the Sky", where the giant Ship has a powerful enough energy generator to maintain magnetic fields to deflect much of the cosmic radiation, but due to a mutiny in the Ship, the energy generator is disabled, and every generation starts suffering from mutations.

Flash Program said at September 17, 2009 7:40 PM:

I think it is not such a good idea, to send humans to mars, without the ability to establish a self-sustaining colony. Achieving self-sufficiency and high standards of living will probably require a form of advanced nanotech so as to be able to manufacture products locally and have structures that are able to repair|maintain themselves and thus allowing for easy expansion. Such an achievement(a strongly established human presence on another world.) is well worth the cost of developing the required technologies.

anonyq said at September 17, 2009 7:54 PM:

Sending senior citizens will probably be the chosen solution.

10 feet thick rock shield is only 2/3 of 80km air and wont be as good in stopping secondaries

Wolf-Dog said at September 17, 2009 9:47 PM:

10 feet thick rock shield is only 2/3 of 80km air and wont be as good in stopping secondaries

-------

In that case we can put 15 fee of rock, and that would be equivalent to 80 km of atmosphere. If the ship is going to be as big as Titanic, since it would not be a major difference. What we need is nuclear propulsion. Also, note that the extra thick shield ONLY has to be in the regions of the ship where humans are residing, not in all parts of the ship.

However, note also that 80 km of atmosphere does not have the same density everywhere. After the first 10 km, the density declines dramatically, and so the 10 feet of rock that I guessed is close to what is needed, since there will also be an artificial magnetosphere powered by the nuclear reactors. The only obstacle is the energy source. Once we master nuclear technology, everything will be easy.

Brett Bellmore said at September 18, 2009 4:05 AM:

"Common antioxidant supplements can radiation harden humans."

You can't really radiation harden people against cosmic rays: They're so energetic they just kill outright the entire column of cells they pass through on their way through the body. The risk there isn't cancer, it's loss of slowly or non-reproducing cell populations. You'd lose a significant fraction of your brain cells on a minimum energy trajectory to Mars.

Brett_McS said at September 18, 2009 5:49 PM:

My prediction is that a human being will not set foot on Mars within a hundred years, and probably never. By the time it would be possible to send a human, robots will be more than capable of doing anything that needs doing. So why bother going to all the extra trouble to send a person? Human inter-planetary space flight will probably always remain science fiction, and human inter-stellar travel is literally impossible - it will never, ever happen. The Earth is all we've got and the human race will never leave home.

Engineer-Poet said at September 18, 2009 6:17 PM:

Or use shielding that's already out there, e.g. hitch-hike to Mars inside an asteroid.

The problem with shielding is that it makes it harder to deal with the other health hazard, zero G.  If the crew arrive at Mars unable to pilot a lander or deal with problems after touchdown, what would otherwise be reversible physical weakness could prove fatal.  You can spin a lightweight craft using something like its booster as a counterweight, but if you have to either spin your shielding too or accumulate enough to cover the entire circle of rotation, you've got a much bigger engineering problem.

Paul F. Dietz said at September 19, 2009 9:21 PM:

The problem with material shielding is that it creates cosmic ray secondaries; There's a wide range of thicknesses over which your radiation exposure *increases* as you add to the shielding. But with thin enough shielding to spare you the secondaries, a solar flare will leave you crispy. So material shielding has to be REALLY thick.

Solar flares could be dealt with using "storm shelters". These would have moderately thick shielding. You'd get galactic cosmic ray secondaries from the shielding, but you'd only be in the storm shelter during bad flares, so that wouldn't be a big problem.

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