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More evasive torpedo

Stop torpedoes and sink ships with them
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Modern anti-torpedo weapons work by creating an explosion in the path of the incoming torpedo, disabling or destroying it.

This torpedo would search for potential incoming countermeasures and fire a rocket to stop itself dead in the water at the right time to avoid likely explosions. It would then speed up again and continue to seek its target.

Voice, Sep 06 2014

8th's "russian supercavitators" http://en.wikipedia.org/wiki/Shkval
In case anyone missed the reference. I can't beleive that someone actually paid for the research on this one. "we want to build an underwater rocket torpedo" "yeah right". But it turns out to work, rather well in fact. [Custardguts, Sep 07 2014]

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       It goes into surly teenager mode, and paints the inside of the torpedo tube black?
not_morrison_rm, Sep 06 2014
  

       Excellent technology for didn't-mean-to-hit-that-button nuclear incidents, if you just want it to perch on a tree or hide in a swamp somewhere in North Carolina for a time.
4and20, Sep 06 2014
  

       // fire a rocket to stop itself dead //   

       You mean use a reaction motor to decelerate ?   

       Have you ever wondered why, after all this time, torpedoes are still propelled by screws, rather than rockets (Russian supercavitators excepted) ?
8th of 7, Sep 06 2014
  

       /torpedoes are still propelled by screws/   

       A screw would let you stop and back up. Do torpedoes do that? Because that is the idea here, I think.   

       You could just have a random path torpedo which swoops and dives unpredictably on the way to the ship.   

       Or how about one that sneaks along the bottom and comes straight up from below? Like the Red Baron but upsidedown. An explosion directly below the ship would make a rough ride, whether from torpedo or countermeasure.
bungston, Sep 07 2014
  

       //Modern anti-torpedo weapons work by creating an explosion in the path of the incoming torpedo, disabling or destroying it.//   

       Got some examples? Not that I doubt you, I just can't find much information on the subject, other than some oblique references to "hard kill" modes for lightweight torpedos to be used in the anti-torpedo role. Are there any dedicated systems?
Custardguts, Sep 07 2014
  

       If you want to stop the torpedo, drogues would work pretty well, and you could get lots of them on one torpedo.   

       Suspect some military somewhere is working on some smaller, flocking torpedoes that follow different paths to the target, then group together before detonation.   

       Some rumour about a Chinese supercavitating submarine, which sounds interesting. But, the launch speed is high, so if it stops, a devil to get it up to high speed again..
not_morrison_rm, Sep 07 2014
  

       //        A screw would let you stop and back up. Do torpedoes do that? //   

       They do not. The screw of a torpedo is powered by a turbine that spins only in one direction and once started does not stop until it runs out of propellant. Stopping or reversing the torpedo might be possible by remotely altering blade pitch, but (I'm guessing) it would take more energy than a conventional torpedo motor is capable of delivering, and restarting would not be possible.   

       On the other hand, there are torpedo-like vehicles that perform as this idea describes: they're called 'unmanned submersibles', and they are slow and easily countered or avoided. You might as well pack a rowboat with gunpowder.
Alterother, Sep 12 2014
  

       ^ That's cuz they're doing it wrong...   

       Hur, hur, hur.
Alterother, Sep 12 2014
  

       //You might as well pack a rowboat with gunpowder.//   

       Al Qaeda tried that, didn't they?
bs0u0155, Sep 12 2014
  

       // // A screw would let you stop and back up. Do torpedoes do that? //   

       They do not. The screw of a torpedo is powered by a turbine that spins only in one direction and once started does not stop until it runs out of propellant. Stopping or reversing the torpedo might be possible by remotely altering blade pitch, but (I'm guessing) it would take more energy than a conventional torpedo motor is capable of delivering, and restarting would not be possible. //   

       We have turbine engines that can be stopped and started arbitrarily. They're used in some series hybrid road vehicles. Changing the speed and direction of the propeller while maintaining the speed and direction of the turbine is also possible; just use a transmission, continuously variable if necessary.   

       And controlling the pitch of the propeller's blades is easy; there are now a few quadcopters that do that for each of their four rotors independently. The shallower the pitch commanded, the less torque necessary to turn the propeller at a given speed. (At zero pitch, the torque is also (almost) zero, because it's not propelling.) So pitch control could only make it easier, not harder, on the engine.   

       I imagine all of this would be controlled by an onboard autopilot, like pretty much all guided missiles—and, I assume, some torpedoes—use.   

       ------   

       OTOH, if you wanted to do this with an underwater missile like the Shkval, it would be considerably harder. To be able to stop and start, you need a hybrid or liquid rocket, solid rockets being unthrottleable, as well as some kind of ignitor (or a hypergolic propellant combination). The supercavity would collapse upon stopping; I don't know if the missile would be able to achieve a high enough speed to reestablish it while experiencing lots of drag from the water. Low-speed maneuverability could be achieved using thrust vectoring (which Shkval 2 is rumored to have) with the rocket at low throttle.   

       Mildly interestingly, I misremembered the Shkval's method of control. This is what I had thought: It has only a small flat plate on its nose that can be tilted in one axis only. This is the only part that contacts the water; its angle deflects the missile one way or the other. The whole missile rolls continuously to enable it to adjust its pitch and yaw alternately (sinusoidally alternately).   

       This is how it actually works, according to Wikipedia: It has four fins (text) or several rods (photo) on its tail end that can be extended or retracted. These dip into the water outside the supercavity, implementing differential drag.   

       It clearly does have some kind of tilting plate on its nose, though.
notexactly, Nov 26 2015
  
      
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