Consider an interstellar spaceship.

It is a rather classical design, somewhat similar to the ISS Venture Star from Avatar:


Although it is not in tractor configuration.

The ship is very long and skinny. At the nose there is a thick, actively cooled radiation shield to protect from collisions with neutral interstellar hydrogen. After that there are the passangers in cryosleep, along with life support equipment and maintenance robots. Than come the very large fuel tanks and another thick shield. At the end there is an antimatter beamed core engine, putting out charged pions almost with c.

The plan is to accelerate with the help of lasers (in the home system) and a foldable photon sail, then accelerate further to 0.7c, and then coast a while, before flipping and starting to decelerate (to achieve orbit in a nearby star system.)

But there is a problem: the ship has to change it's orientation by 180 degrees to start deceleration. Inevitably it would travel sideways for some time, while having the highest relative velocity to the interstellar medium.

Assuming that it takes 5 minutes to rotate the ship, could the radiation hitting the unshielded side cause structural damage and/or harm the passangers?

Should additional shielding used on the cabin's side walls? Or would the minimalist shielding against galactic cosmic rays suffice for a short period of time?


This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

  • $\begingroup$ Is there a reason that it doesn't get hit by any radiation on the sides during regular space-flight/why doesn't it need radiation shielding before worrying about the rotation bit? $\endgroup$ – Mithrandir24601 Apr 6 '17 at 21:15
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    $\begingroup$ @Mithrandir24601, at 0.7c, the majority of "background" radiation will come from ahead, and at the same time, "induced" radiation from encountering otherwise-ordinary interstellar particles at too high a speed will come exclusively from ahead. $\endgroup$ – Mark Apr 7 '17 at 1:17
  • $\begingroup$ So when the OP says 'could the radiation...' do they mean 'radiation' or 'neutral interstellar [particles]'? $\endgroup$ – Mithrandir24601 Apr 7 '17 at 8:56
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    $\begingroup$ @Mithrandir24601 At that speed, "neutral interstellar particles" are no longer "neutral interstellar particles." From that reference frame, they are particle radiation. Or, at least they are close and might as well be considered such; is there a specific limit for the definition of particle radiation? 0.9c? 0.999c? Anyway, at that speed the distinction is a nitpick. OPs question is pretty obvious. "Are we safe during the flip?" $\endgroup$ – Loduwijk May 2 '17 at 21:00

No real threat to the passengers

The ISV has multiple measures to deal with the few threats in interstellar space. From your link:

Although intense magnetic fields are used to deflect stray gas molecules, the occasional dust grain requires a physical barrier. The shield is in multiple layers, spaced one hundred meters apart. Impact of a debris grain (traveling at a relative speed of 0.7C) with the first layer of the shield causes vaporization into a plasma. The spray of plasma particles strikes the second layer, and the impacts cause spalling from the back of the second layer. These particles are stopped by the third layer. A fourth layer acts as a backup in the unlikely event that something gets past the third layer. Once cruise speed is reached, this shield is detached and moved by small thrusters thousands of miles in front of the ship to improve survivability if a larger particle of debris is encountered.

This combination of safety measures would be sufficient to protect the ship during this maneuver, and the ship would not perform this maneuver at all if larger material was present.

Even without the shield the passengers would be relatively safe. The Breakthough Starshot proposes a postage stamp sized craft to be sent to Alpha Centauri at .2 c. According to this paper, the erosion on the unshielded surface is only .5 mm deep over a ~4 year journey. So 5 min at .7 c won't be a big issue.

With the shields in place little if anything would happen to the spacecraft. Without them, there will be very minor surface erosion, heating, and some charging of the spacecraft.


For those concerned by radiation touched off by relativistic impacts this states that the HAB sections of the ship are made of nonmetallic compounds which reduce this effect.

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    $\begingroup$ I have read that about 25% of interstellar medium is neutral, and therefore can not be effectively deflected by magnetic fields: en.wikipedia.org/wiki/Interstellar_medium However, the ejection of the shield actually solves the problem. $\endgroup$ – b.Lorenz Apr 7 '17 at 14:15
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    $\begingroup$ Even then the erosion rate from uncharged particles will be minor for that 5 min. The biggest threat out there is still cosmic rays. $\endgroup$ – Joe Kissling Apr 7 '17 at 14:26

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