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Torch Missiles v Kirklin Mines

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  • rmrobinson1227
    This is mainly a belated reply to points Kirk made some weeks ago, and in fact back to whenever he first came up with the devilish Kirklin mine. For someone
    Message 1 of 3 , Sep 9, 2003
      This is mainly a belated reply to points Kirk made some weeks ago, and
      in fact back to whenever he first came up with the devilish Kirklin
      mine.

      For someone with a taste for very high combat velocities (at least
      compared to the handy AV reference point), I can be *really* slow. :)
      But I finally came up with - I think - a way for the torch missile to
      beat the Kirklin mine.

      First, a brief recap of the problem. My "classical" torch missile is
      a fairly large, expensive vehicle - comparable in size/mass/cost to an
      SLBM or a jet fighter. It approaches its target at very high relative
      speed, ~100 km/s, and bursts into fragments as it reaches the target's
      laser PD kill zone, perhaps 1000 km from target. The cloud of
      fragments shotguns the target, saturating the laser defense and
      filling its jink envelope with junk. :>

      Kirk's countermeasure is what I dubbed a Kirklin mine. It is a small,
      (relatively) cheap chemfuel target seeker. A solid fuel booster
      launches it out along the torch missile's approach track, some minutes
      in advance. It intercepts the torch missile well before the latter
      comes into effective burst range, and crashes into it.

      If you launch the Kirklin mines TOO early, the intercept point will be
      so far out that the torch missile - with less acceleration but much
      more delta v - can swerve around the mine and still re-acquire its
      target. But there's a pretty wide band, maybe 3000-50,000 km from
      target, where the mine can either kill the torch missile beyond its
      effective burst radius, or force it to miss the target the mine is
      protecting.

      Since the Kirklin mine is only a few percent of the cost of a torch
      missile (say, $250,000 equivalent v $10 million), you can use several
      and still have a very cost-effective defense.

      These damn things have perplexed me for several months, because they
      seemed to rule out the torch missile as a reliable ship killer.

      To beat it, I first have to abandon the simple shotgun approach.
      Instead, I'll have the torch missile carry a dozen or so submunis.
      These submunis are very similar to Kirklin mines themselves. They
      will be deployed shortly before the missile bus reaches the mine(s).
      Within the mine's effective zone, the chemfuel submunis have enough
      delta v to counter evasive maneuvers by the target ship.

      Right away, this reduces the Kirklin mine's cost-effectiveness
      advantage by about a factor of 10, because you'll have to launch
      enough of them to take out all the submunis, instead of just whacking
      the torch missile bus.

      Using my swagged figures, a torch missile plus 12 submunis costs $13
      million. 28 Kirklin mines - two to double-team each submuni, plus two
      for the torch missile bus - cost $7 million. At this point, the mine
      does still have a cost-effectiveness advantage, though much less than
      before.

      But ... this is one situation where decoys are viable. I can afford
      to carry a couple of dozen decoys as well as my submunis. These can
      be anything from foil balloons to "realistic" dummy submunis (but far
      cheaper since they're inert, without guidance, thrusters, etc.). To
      sensors, the decoys are indistinguishable from the real deal.

      Eventually the real submunis *will* have to maneuver to intercept the
      target - but by then they will have passed the mines, or at least any
      "first wave" of mines. By careful deployment of the mines, combined
      with evasive maneuvers, you can probably fox out a good many of the
      decoys, but you'll have to expend quite a few mines to do so - and you
      still need to take out the submunis.

      I doubt that this kills the Kirklin mine as a useful defensive measure
      in the right circumstances, but I do think that it evens up the
      playing field, and restores the torch missile as a viable weapon
      (assuming the tech allows it in the first place).

      -- Rick
    • ac_jackson
      ... You know, this whole kirklin mine debate is a repeat. Here was my last statement in the previous debate:
      Message 2 of 3 , Sep 9, 2003
        --- In sfconsim-l@yahoogroups.com, "rmrobinson1227" <Lyonesse@c...> wrote:

        You know, this whole kirklin mine debate is a repeat. Here was my
        last statement in the previous debate:

        http://groups.yahoo.com/group/sfconsim-l/message/39605

        I'm pretty sure the same logic, with variants, can apply to just about
        any missile/countermissile tech design.
      • rmrobinson1227
        ... about ... I think you re right - in fact, the solution to my problem (i.e., trying to get through mine defenses to nail the ship) is implicit in your
        Message 3 of 3 , Sep 10, 2003
          --- In sfconsim-l@yahoogroups.com, "ac_jackson" <ajackson@i...> wrote:

          > You know, this whole kirklin mine debate is a repeat. Here was my
          > last statement in the previous debate:
          >
          > http://groups.yahoo.com/group/sfconsim-l/message/39605
          >
          > I'm pretty sure the same logic, with variants, can apply to just
          about
          > any missile/countermissile tech design.


          I think you're right - in fact, the solution to my problem (i.e.,
          trying to get through mine defenses to nail the ship) is implicit in
          your analysis. It just took me 2 months to stumble onto it. :)

          Here's the key paragraph from your earlier analysis:


          > Now, a point here: if we change reference frames, we just have two
          objects and
          > clouds on a collision course; the clouds hit first, followed by the
          larger
          > objects. There is only one difference between these two clouds: the
          mine wants
          > to destroy the missile, the missile wants to bypass the mine.


          You are right that the problem is nearly symmetrical. But take it to
          the next step. My overall objective, after all, is not to kill the
          mine so as to protect my missile: it's to kill your *ship* that is my
          torch missile's target.

          So, the torch missile doesn't release a cloud of submunis as
          anti-antimissiles to protect itself against the mine - it releases
          them to go directly after the target ship. Once it's done that, I
          don't much care what happens to the torch missile bus. It is
          expendable, and expended. (In practice it can continue to close on the
          target ship, effectively just one more object in my cloud of
          target-seekers.)

          So, instead of looking at the chance of the single big torch missile
          getting through your defensive cloud, we're looking at the cumulative
          chance of at least one of my submunis getting through.

          Suppose that the chance of each of my submunis avoiding one mine is 20
          percent, a bit less than your theoretical optimum 25 percent. If you
          "double-team" my submunis, the chance of each getting through is 4
          percent. Putting it another way, your mines have a 96 percent chance
          of killing any given submuni.

          If I remember my basic stats correctly, your chance of killing ALL of
          my submunis is 0.96^N, where N - 1 is the number of submunis my torch
          missile released. (The Nth "submuni" is the torch missile bus)

          So, if my torch missile releases 20 submunis, and your defensive cloud
          is 42 mines (2 for each submuni plus my bus), the chance of your mine
          cloud stopping ALL of them is 0.96^21, or 0.42 - so the torch missile
          has a 58 percent chance of getting a submuni through your mine
          defense. If the same 20 percent evasion probability applies to ships
          as to the submunis, I have a 46 percent chance of actually scoring a
          hit.

          If I launch two torch missiles (and you launch 84 mines), I have a
          better than 2:1 chance that one submuni will get through to hit your
          ship. Whether this pays for me depends on the relative cost of torch
          missiles and mines/submunis - and for that matter the relative cost of
          torch missiles and ships (and how many hits, if any, a ship can expect
          to survive).

          But to a first approximation, the balancing point is about when the
          torch missile's payload of submunis costs about as much as the missile
          bus does - so that it costs as much for you to have a 50-50 chance of
          stopping my torch missile as it costs me to launch it.


          Several other factors could complicate this basic analysis, some
          tipping one way and some the other.

          Favoring the defense:

          1) If you have decent laser PD, as well as mines, it probably doesn't
          do for me to get just one submuni past the mines - I have to get
          enough through to saturate the laser defense.

          2) Loading my torch missile with submunis makes it more expensive, so
          I can't use as many. The need to carry a payload (which my
          "classical" missiles didn't, except for a tiny bursting charge) also
          reduces performance relative to their targets.

          Taken together, these factors can price torch missiles out of the
          market.

          Favoring the attack:

          1) The torch missile can release decoys as well as submunis. There is
          no clear way to distinguish them till the submunis have to maneuver to
          counter evasive jinking by the target ship. This reduces the mine's
          engagement envelope.

          2) Submunis and mines are both small (about the size of an artillery
          shell) and agile. Hitting a guided bullet with another guided bullet
          is probably much harder than hitting a barn with a bullet, even a barn
          taking evasive action. So the chance of a mine taking out a submuni
          is probably a lot less than its chance of taking out a big missile bus
          would be - or than the chance that a submuni that gets through the
          mines will hit the target ship.

          Based on ABM experience, a 75 or 80 percent chance of a mine hitting a
          submuni seems optimistic. 50 percent might be more likely. In that
          case, you'd need to quadruple-team each submuni to get a 94 percent
          chance of killing one, and still have less than one in three chance of
          killing a busload of 20. This can wipe out the cost-effectiveness of
          the defense.

          3) If I'm investing in offensive firepower while you're investing in
          defense, I have the initiative. This is hard to quantify, but it can
          balance out the cost of the torch missiles themselves, if I can launch
          them from cheap ships that don't need any defenses to speak of because
          they don't get attacked. :>


          In summary, as in the underlying Purple/Green debate, this is all
          highly sensitive to specific inputs - relative cost of torch missiles
          and mines/submunis, probability of a mine taking out a submuni, etc.
          Tweaking input assumptions within a fairly narrow range can have a
          dramatic effect on the expected results.

          -- Rick
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