In space somewhen in the future there's need to build a space station able to sustain heavy railgun fire.

How would you design it? I was thinking about building something similar to a 17th century star fort but in 3 dimensions, but after making a model on SketchUp I'm beginning to doubt its viability.

Is there anything that could be done?

Supose you are dealing with almost infinite funds, you have a foundry in space, unlimited materials, unlimited energy (just to build the station), etc, don't worry about logistics for now.

It would be great for it not exceding the dimensions of an imaginary cube with an arista 2 km long.

This is my 4(*2) points star fort from SketchUp:8 pointed cubic star fort

I have developed the design a bit more, 8+6 cubic star:14 pointed cubic star fort

  • $\begingroup$ Can your station detect incoming attack with enough advance warning to rotate itself? Would attacks come from single direction (single ship or group of ships attacking from one direction) or multiple directions (multiple ships surrounding the station)? $\endgroup$
    – M i ech
    Commented Dec 9, 2020 at 21:05
  • 2
    $\begingroup$ At the speed that a spaceship-fired railgun round is likely to travel, conventional bullet dynamics go out the window. Even at very low incidence angles there won't be ricochet and your best bet is thick or staggered armor like that which is used on the ISS $\endgroup$
    – Dragongeek
    Commented Dec 9, 2020 at 22:21

3 Answers 3


Ricochets don't happen with railgun charges

Railgun projectiles viable for space combat will have very high velocities, at least ten kilometers per second. At these speeds, projectile delivers more kinetic energy than it's own mass in TnT. So it doesn't deflect, it vaporises upon contact like micrometeorites do, and the resulting plasma and shrapnel does the damage, which looks like this:

enter image description here

The far superior option would be to use a layered armor consisting out of thin sheets separated by empty space. The projectile hits the first layer, vaporises, and plasma and debree from the impact disperses in the empty space behind the first layer, oing greatly reduced damage to the secon layer, and so on.

enter image description here

Bonus points in that whipple shield armor is very light compared to "proper" thick layers of armor.

And here is where you don't actually want to have too great angles between your craft surfaces and the enemy line of fire - because then the impacts will create larger gaps in your armor (Ejecta of the first layer will be directed sideways instead of straight down), reducing it's lifespan.

  • $\begingroup$ " And here is where you don't actually want to have too great angles between your craft surfaces and the enemy line of fire - because then the impacts will create larger gaps in your armor (Ejecta of the first layer will be directed sideways instead of straight down), reducing it's lifespan." Sloped armor would also increase the effective thickness of the spaces between the armored sheets, though. $\endgroup$
    – nick012000
    Commented Dec 10, 2020 at 4:37
  • $\begingroup$ So you would design it like a series of concentric spherical sheets of armor? $\endgroup$ Commented Dec 10, 2020 at 9:47
  • $\begingroup$ "Sloped armor would also increase the effective thickness of the spaces between the armored sheets, though." the whole point of the Whipple shield is to use thin armor plates. Slopes will just cause the projectiles to carve out larger by surface oval holes in the underlying layers, decreasing their effectiveness. $\endgroup$ Commented Dec 10, 2020 at 13:14

1. Station is thick.

Your station is stationary. That is how it got its name. Around the working part of your station you have strapped many large rocks of various types. You found these rocks in the neighborhood. Your station looks like a clump of rocks because for the outer kilometer, that is what it is. These rocks are not on a solid scaffold but frozen in place with icy sand. Incoming energy expends itself breaking the rock and melting the ice. Easy come easy go.

Thick Station is massive. Good thing it is stationary!

This would work against low power projectiles fired at close range. Those of you unfamiliar with the scifi show The Expanse: they do a great job depicting railguns like this.

2. Station sees them coming.

Relativistic velocity railgun projectiles still could mess up Thick Station. These would be fired from a specialty platform at some distance. They might be very fast, but light is faster. Acitve and passive sensors using the whole spectrum of EMR will easily see a fast moving incoming projectile. From a defensive standpoint a railgun projectile in space is nice as it cannot maneuver and once detected its course can be known.

Thick Station fires at the projectile, like an AEGIS system. Projectiles intercept the incoming railgun projectile at distance. The station's defensive projectiles are not moving fast because they do not need to. If the railgun hits one, both are converted to plasma and the plasma molecules rain harmlessly on the thickness of Thick Station. The automated defenses on Thick are good shots but usually send out a few projectiles to be sure. This works against space debris just as well.


Star Fort still seems to have too many flat surfaces. Make it spherical. That will offer sloped surfaces in all directions. Then - put multiple layers of armor on it. External layers could be made from thin sheets of metal (the term is I think Whipple shield), empty spaces between layers could be left empty or could be filled with aerogel to reduce spalling and shockwave expansion. Only deeper layers would be made from hard, dense metal. The idea is that fast moving projectiles will vaporize on contact with Whipple shields, energy will be dispersed before it reaches main armor. Sections of lighter armor are easier to replace after bombardment.

Because this is station, which doesn't have to move you could use as much mass as you want. For example for additional protection you could put water ice right below main armor as radiation protection and emergency heat sinks.

And put a lot active defenses between the fort and its enemies because even the best armor wont do much good against sustained railgun attack.

  • 2
    $\begingroup$ While sphere has optimal surface-to-volume ratio, it's drawback is that it presents flat or near flat surface from every possible angle. Any shot fired along radius hits at perfect angle (normal to surface) maximising both damage and chance to penetrate armour. Exactly half of cross section of sphere presents armour at angle of 45 degrees from normal or smaller, from every possible angle. Angle required for ricochet depends on many factors, but typically angles need to be shallow. As required angle increases, section capable of deflecting very quickly shrinks to outer edges of cross section. $\endgroup$
    – M i ech
    Commented Dec 9, 2020 at 21:14
  • $\begingroup$ Still, sphere is better than flat surfaces. If enemy can put a missile straight along the radius of the spherical fort it can also hit those flat areas of the star fort. Ideally station that depends on ricochets for defense would have to be made into a elongated cone, with tip directed at the enemy. Not very practical, it would have to be able to quickly move and would be vulnerable to attacks from sides. I think sphere is the best solution for the problem. $\endgroup$
    – Zjerzy
    Commented Dec 9, 2020 at 21:27
  • $\begingroup$ @Zjerzy I have updated the question with the final image of what I was intending to develop. a 14 pointed star. Almost no flat surfaces, unless you make it 2 km high. $\endgroup$ Commented Dec 9, 2020 at 21:33
  • $\begingroup$ What about making it like two very sharp cones joined by the base and being highly maneuverable? That way, it would be able to point the point of one of the cones towards the attacker and increase the chances of ricocheting while reducing the cross section to a minimum. Also, I was looking for a passive defense system. $\endgroup$ Commented May 16, 2021 at 11:14
  • 1
    $\begingroup$ But there will be trade offs. Cone is inefficient because it wastes space. Sections of cone armor will be more difficult/expensive to produce in comparison to straight surfaces of the star fort. High maneuverability is always good but this means big engines and fuel tanks that could be used for storage and weapons (that what your star fort probably is for?) At some points your space station will cease to be a station and become a ship. Those trade offs could make construction of star fort more interesting. $\endgroup$
    – Zjerzy
    Commented May 16, 2021 at 13:06

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