Assume you have a sophisticated nuclear (thermal or whatever comes to mind) propelled spaceship for your summer vacation on Mars. Half way there Houston calls and informs you about an inbound solar storm.

Unfortunately, you bought your ship at "Honest John's used space ship and spare parts" and you have no radiation shelter on board. So in a desperate attempt to save you and your crew, you turn the ship so that the nuclear reactor points at the sun in the hope that its radiation shielding saves you from the solar storm.

  • Is this in principle even possible, i.e. is the radiation emanating from a solar storm directed? Maybe when paired with additional magnetical shielding?
  • Is it practically feasible, i.e. can you turn your ship in the time you have after a warning? Could you have your ship always pointing away from the sun?
  • Is it economical, i.e. would there be additional requirements on the shielding of your nuclear reactor and would they outweigh a typical storm shelter? I know this depends on your reactor size, so I am just asking for order of magnitudes here.
  • 2
    $\begingroup$ In much of the solar system, solar storms are omnidirectional (space.stackexchange.com/questions/14353/…), so shielding on one side won't help. $\endgroup$
    – Hobbes
    Commented Mar 16, 2016 at 10:55
  • $\begingroup$ @Hobbes Just within magnetospheres $\endgroup$ Commented Mar 16, 2016 at 11:03
  • $\begingroup$ I was going by Mark Adler's comment "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.", this would apply outside the magnetosphere as well. $\endgroup$
    – Hobbes
    Commented Mar 16, 2016 at 11:08
  • $\begingroup$ Why are you asking us? Ask John. He's honest. $\endgroup$
    – corsiKa
    Commented Mar 16, 2016 at 16:05

2 Answers 2


The basic idea here is to turn to have the shield you have towards the Sun. That does actually work, because the radiation from the Sun is directed, with a few exceptions: First, inside a planetary magnetosphere, charged particles are bent, and form radiation belts, for example the Van Allen belts. There, shielding is a bit more difficult. Secondly, that is also a problem close to the poles of the Sun, but there "avoiding melting" is a bigger concern. As most spacecraft have attitude control systems, like RCS thrusters, it can be rotated in just a few minutes. That is by far shorter than the warning time for solar flares. (Even in the worst cases several hours.)

But! Solar flares are not the only radiation concern in space, as the cosmic radiation is large enough to pose a serious threat to the health of the cosmonauts. In order to protect them from that, you are going to need a shelter in either case, making use of just the engine shield insufficient.

  • $\begingroup$ But which other sources of radiation would require a dedicated "shelter" (i.e. a room that is only used for a relatively short period of emergency)? I always assumed that the rest of the cosmic radiation is either relatively uniform (so you would have to stay sheltered all the time) but low-intensity or unpredictable (like gamma ray bursts) and deadly. $\endgroup$
    – choeger
    Commented Mar 16, 2016 at 11:50
  • $\begingroup$ @choeger Non necessarily a shelter, overall shielding of the living compartments is more what you would need. $\endgroup$ Commented Mar 16, 2016 at 11:58
  • $\begingroup$ Right, buts that something you need anyway and it wouldnt help against a solar storm. But you agree that it might suffice to shield your reactor and pressurized compartments and not bring a (heavy) additional shelter? $\endgroup$
    – choeger
    Commented Mar 16, 2016 at 12:03
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    $\begingroup$ @Hohmannfan I like how you assume the crew are Cosmonauts, even though the OP states that the crew were warned about the solar flare by Houston ;) $\endgroup$
    – Dean
    Commented Mar 16, 2016 at 12:59
  • 1
    $\begingroup$ @DanNeely The OP says "summer vacation on mars" $\endgroup$ Commented Mar 16, 2016 at 14:07

Yes, such a ship would still need a storm shelter. The reactor shielding is not enough: when you're in a solar storm (i.e. a cloud of particles ejected by the Sun), the particles will come at you from all directions.

Warning in time is possible: NASA already does this. The SOHO satellite observes solar flares and CMEs. Because the flare/CME moves at in the region of 300-3000 km/s (i.e. up to 1% of light speed) we get ~ 12 hours advance warning on Earth, more if you're further out in the solar system.

Instead of using mass for shielding, I suspect a nuclear-powered spaceship would rely on a magnetic shield. This would require on the order of 500 kW, well within the power generation capability of even a small nuclear reactor. This also avoids nasty secondary radiation effects you can get from mass shielding.


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