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Projectiles in vacuum

  1. Jan 25, 2007 #1
    I don't know is this is the best subsection i which to post this question. Please indicate me the right place, eventually. And forgive me for not so sublime english, as I'm not a naturally english speaker.

    Now...
    I think it's proven that the most effective projectile, in terms of penetration, is a rod. So modern weapons are moving toward Kinetic Energy rounds with a rod penetrator. The penetrator has the problem of tumbling in flight, that is accentuated by rotation, (so all cannons are going toward a smooth bore). The stability issue is resolved by stabilizing fins, as an arrow.

    Now, if a penetrator was to be fired in vacuum (space), what methods would be used to stabilize it's flight? But most important, would it tumble? And if shot from a railgun, would it tumble?
     
  2. jcsd
  3. Jan 25, 2007 #2

    ranger

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    Have you giving any thought about newton's first law?
     
  4. Jan 25, 2007 #3
    yes, the point is, when fired from a conventional gun, the penetrator is contained in a sabot that is discharged in flight, and the pressure of the explosion of the propellant is uneven. All of this, and other things (wind pressure on imperfections of the rod etc) causes the rod to tumble and rotate, which is countered by applying fins.
    Fins are not applicable in space, as the drag would be too small. The penetrator may eventually discharge some material (gas?) to remain aligned to the direction of movement, but how to determine direction in space without acceleration?
    Railgun may accelerate the projectile in a smoother manner, maybe preventing rotations, but it would eventually need sabot if the projectile is not conductive.
    So maybe in the end the only solution is to abandon penetrators and return to old spherical projectiles?
     
  5. Jan 25, 2007 #4
    Perhaps rotating the projectile quickly about its axis. For instance, the barrels in rifles are grooved (called rifeling the barrel) so that a bullet will leave spinning. This apparently results in a tremendous increase in the accuracy of the bullet. Shotguns lack rifeling because they are made mainly for scattershots. Consequently, even a well aimed slug has a poor accuracy over any appreciable distance. I am guessing the increase in accuracy is due to some form of precession (the same thing that stabalizes bikes and spinning tops). If so then this should work for vacuum projectiles since precession is linked to the moment of inertia and has nothing to do with an external quantity such as air. I'm not entirely sure about this though and so maybe one of the more savvy forum contributors could confirm or debunk...
     
  6. Jan 25, 2007 #5
    Hmm. I'm going to correct what I said before. Rotation causes tumbling in a finned projectile. The problem with stabilization by rotation si that the longer the projectile is in relation to diameter, the faster must be spinned to provide stability. I don't know how faster in relation to ratio. Rifled guns can't spin fast enough a penetrator.
    So, now the question might be; how to spin very fast a rod penetrator with a railgun?
     
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