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Will it be safe for humans to fly to Mars?
Sending human travelers to Mars would require scientists and engineers to overcome a range of technological and safety obstacles. One of them is the grave risk posed by particle radiation from the sun, distant stars and galaxies.
Answering two key questions would go a long way toward overcoming that hurdle: Would particle radiation pose too grave a threat to human life throughout a round trip to the red planet? And, could the very timing of a mission to Mars help shield astronauts and the spacecraft from the radiation?
In a new article published in the peer-reviewed journal Space Weather, an international team of space scientists, including researchers from UCLA, answers those two questions with a "no" and a "yes."
That is, humans should be able to safely travel to and from Mars, provided that the spacecraft has sufficient shielding and the round trip is shorter than approximately four years. And the timing of a human mission to Mars would indeed make a difference: The scientists determined that the best time for a flight to leave Earth would be when solar activity is at its peak, known as the solar maximum.
The scientists' calculations demonstrate that it would be possible to shield a Mars-bound spacecraft from energetic particles from the sun because, during solar maximum, the most dangerous and energetic particles from distant galaxies are deflected by the enhanced solar activity.
Journal Reference:
M. I. Dobynde, Y. Y. Shprits, A. Y. Drozdov, et al. Beating 1 Sievert: Optimal Radiation Shielding of Astronauts on a Mission to Mars [open], Space Weather (DOI: 10.1029/2021SW002749)
(Score: 3, Informative) by c0lo on Wednesday September 15 2021, @02:16PM (7 children)
Just put the water tanks between the Sun and the travelers to Mars. 10cm of water will halve the γ ray intensity [eu.com] α and β aren't of any concern.
https://www.youtube.com/watch?v=aoFiw2jMy-0
(Score: 1, Interesting) by Anonymous Coward on Wednesday September 15 2021, @03:01PM (2 children)
It's neither the gammas or the betas that are the problem, it is the high energy cosmic rays (mostly protons). Shielding is complicated in that as you add more shielding, you decrease the flux of cosmic rays, but you increase the flux of secondary particles generated in the shielding, so it is an optimization problem. I will have to look at the paper in detail later to see what they say about solar flares (CMEs), which would be more prevalent during solar max.
(Score: 0) by Anonymous Coward on Thursday September 16 2021, @12:19PM (1 child)
As I understand it you need low atomic number or Low-z materials to do the mopping up of any spallation neutrons generated. Hence the water / boronated ethylene.
The radiation shield needs to be basically a long cylinder they can all fit inside of.
(Score: 0) by Anonymous Coward on Thursday September 16 2021, @12:23PM
I think Low Z materials make poor spallation targets, its like pool or billiards basically? Something about elastic collisions. I'm not a particle physicist obviously.
(Score: 5, Interesting) by Immerman on Wednesday September 15 2021, @03:21PM (3 children)
They were specifically looking at *particle* radiation, so gamma rays weren't considered. Meanwhile alpha and beta should be mostly blocked by the ship's skin, but the resulting ionization could still present shocking (heh) difficulties.
Heck, I imagine just the pointing the engines and fuel tanks at the sun would do an excellent job of shielding from solar radiation. I'm not sure how the shielding properties of liquid methane and oxygen compare to water, though with all those hydrogen bonds methane at least should compare pretty well, but having many meters of the stuff (on average, it'll be floating around) should do the job nicely.
But that's less than half the radiation - at Earth's orbit only about half the radiation comes from the sun while the other half, including most of the extreme high energy radiation, comes from distant astronomical sources. And as you move further from the sun on your way to Mars the solar portion decreases.
Since effectively shielding against cosmic rays is currently pretty much impossible given the mass constraints, traveling at solar maximum to minimize the interstellar radiation by taking advantage of the shielding effects of the denser solar wind seems to make sense.
However, I can't help wondering just how dramatic the difference really is.
(Score: 1, Informative) by Anonymous Coward on Wednesday September 15 2021, @05:23PM
Skimming the article suggests a nearly 3:1 reduction in cosmic rays. As cosmic rays are more dangerous than solar radiation that seems significant.
(Score: 0) by Anonymous Coward on Wednesday September 15 2021, @07:30PM (1 child)
Not quite that simple. During solar minimum, when the solar magnetic fields (close to the ecliptic plane) are generally described as Archimedean spirals, higher energy charged particles from flares and other disturbances predominantly travel along those spirals, which at around 1 AU are at angles around 45 degrees, so you'd want to point your engines about 45 degrees towards the western limb. However, at solar maximum, it is all a mess. The spirals are disturbed by all sorts of stuff and your solar magnetic field angle at your spacecraft can be all over the place, meaning that your particles will be all over the place. Plus you add in the spiral trajectories of charged particles due to Coulomb forces, it gets even messier. That's why galactic cosmic rays are largely isotropic in their arrival directions all the time. Solar less so, but much more jumbled up during solar max.
(Score: 2) by Immerman on Thursday September 16 2021, @01:38PM
Hmm, I hadn't thought of that. So I suppose you would want shielding adequate for solar particle radiation in pretty much every direction. You'd have to decide whether it makes more sense to point the engines at the densest (highest energy?) incoming particle concentration, or directly at the sun to block the neutral and EM stuff. My guess would be the latter, unless they were hit by a tide of something really serious.
Of course, I think the article was actually discussing cosmic ray exposure inside a radiation shield (10-30g/cm^2?) anyway, so that's probably exactly what they were visualizing.