This question proposes building a satellite to deflect solar ionizing radiation from Mars. But there are two sources of radiation: the sun and 'everything else' (cosmic radiation). How much radiation can you expect from these sources in orbit around Mars?

Does a shield that removes solar radiation alone (1), result in a survivable environment, either in orbit or on Mars' surface?

1: not just the satellite from the linked question. You could build a ship that has a thick shield in the sun-facing direction only, for example.

  • $\begingroup$ There isn't really a ratio, since the solar energetic particles are highly time varying, as well as directional. You could get lucky or unlucky with solar flares/CMEs coming your way or not during your voyage. $\endgroup$ – Mark Adler Mar 6 '16 at 15:41
  • $\begingroup$ I'd be happy with a ballpark figure, but I'm not the one designing Mars missions :-) $\endgroup$ – Hobbes Mar 6 '16 at 16:29
  • $\begingroup$ I see you are already aware of cosmic rays etc though this might still help: en.wikipedia.org/wiki/Cosmic_ray - there are some topics in the page that touch on the health connection on Earth. $\endgroup$ – Puffin Mar 6 '16 at 16:48
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    $\begingroup$ The ballpark figure is that the solar protons can vary from about 0% of the galactic cosmic ray background, to about 100,000 times the cosmic ray background during a solar proton event. $\endgroup$ – Mark Adler Mar 6 '16 at 17:50

Galactic cosmic rays (GCRs) provide a steady background radiation that poses health risks to humans on the year time scale. That is, over a year with typical spacecraft shielding you will get on the order of the total lifetime dose allowed in Earth occupations. Not really a big deal at all, seeing as how you are on a once-in-a-lifetime adventure of epic proportions.

Solar proton events (SPEs) on the other hand are episodic and huge, ranging up to 100,000 times the flux of the GCRs, with each lasting on the order of days. They are directional and not all that common. But with a little bad luck, they can kill you. We were somewhat fortunate that none of the Apollo missions saw any major solar proton events. It helped of course that the missions only lasted a week or two.

While flying the Mars Exploration rovers to Mars, we experienced such an event around Halloween of 2003. It resulted from one of the largest solar flares ever observed. The spacecraft survived, since they were designed for that (unlike humans), but the radiation took out our star scanners for about two weeks. The star scanners were seeing thousands of stars that weren't stars, preventing them from recognizing star field patterns. So no turns or maneuvers were possible during that time. Several FPGAs also were taken out of service due to single-event upsets, but we were able to reset those to restore their operation. Here is a plot of the event as seen by the GOES 11 satellite at Earth at the time:

GOES 11 Oct 30, 2003 solar flare event

Note that the vertical scale is logarithmic, showing about 10,000 times the background during the event.

At your location, the SPE protons are essentially omnidirectional, so you can't just shield on one side. The directionality is on the order of 10%, so no help there.

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  • $\begingroup$ Good answer. Does the omni-directionality at Mars arise because of the nature of the Sun's rotating magnetic field, i.e. regardless of the absence of a strong magnetic field from Mars itself? $\endgroup$ – Puffin Mar 7 '16 at 0:04
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    $\begingroup$ It's mainly because the velocity of the individual protons is very high compared to the velocity of the slug of plasma emitted by the Sun. So when you are inside the slug of plasma, protons are coming at you from all directions. $\endgroup$ – Mark Adler Mar 7 '16 at 1:05
  • $\begingroup$ Does this apply equally at the scale of Mars as a whole, i.e. the SPE fluence is similar for a person on the surface, regardless of whether they are on the sunlit or dark side? $\endgroup$ – Puffin Mar 7 '16 at 1:17
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    $\begingroup$ This only applies in deep space. Not in a low Mars orbit, and certainly not on the surface, with significant shielding from the atmosphere. $\endgroup$ – Mark Adler Mar 7 '16 at 5:47
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    $\begingroup$ Being on the surface of a body with no atmosphere cuts the flux in half right there. The atmosphere of Mars has a much greater effect, reducing the GCRs by about a factor of four (as I recall), and the solar protons by much more. This abstract provides some numbers from large solar flares. $\endgroup$ – Mark Adler Mar 7 '16 at 15:04

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