From: chakatfirepaw@gmail.com   
      
   On Thu, 27 Oct 2016 07:36:33 -0700, Mikkel Haaheim wrote:   
      
   > Le samedi 1 octobre 2016 10:22:23 UTC+2, Rick Pikul/Chakat Firepaw a   
   > écrit :   
   >   
   >   
   >> > I will have to review my original statements. I do not know why I   
   >> > would have chosen a figure such as 10^8 km^2.   
   >>   
   >> It's what you need to hit when using unguided projectiles, you need to   
   >> saturate an area thousands of kilometres across.   
   >   
   > It really isn't. A saturation of (100 km)^2 would be sufficient for the   
   > original escape manoeuvre parameters. That can be cut significantly once   
   > you have determined the mean path and orders of deviation.   
      
   Those parameters were based on what it would take to avoid a given shot,   
   not what kind of shot could be avoided.   
      
   >> > As I said, I will go through my original posts. Keep in mind, that my   
   >> > response was in the context of SeaWasp's suggestion of how easy it   
   >> > would be to avoid a 50 km asteroid. If you are willing to lob these   
   >> > around, even your erroneous quadrillion tonnes would be "reasonable".   
   >>   
   >> Avoiding a 50km asteroid and avoiding a 50km wide cloud of shot are of   
   >> equal difficulty.  The only way the cloud of shot can be harder to   
   >> avoid through blind jinking is if it covers a larger area.   
   >   
   > Except that we are talking about a 100 km wide cloud, which will be 4x   
   > more difficult to avoid, and virtually impossible to avoid given a 50 km   
   > window of manoeuverability. Granted, both sides of the matter can be   
   > "tweaked". Actual success generally depends upon who has the best   
   > intelligence and planning.   
      
   A 100km wide cloud is also trivial to avoid:  1 arc-second worth of   
   normal thrust is a shift that maxes at 750km for a 1AU orbit.  1 arc-   
   second out at 6AU is 4500km.   
      
   > Also, keep in mind that this was under the assumption that the target   
   > will have months of notice. Not very realistic, IMHO, given the minimal   
   > reflective cross section of the shot, and the virtually null emission.   
      
   If 'stealth shots' are even conceivable than isolated military platforms   
   will be engaged in avoidance as a matter of course.   
      
   >> (Assuming a triangular grid would be right, although I approached it as   
   >> hexagonal packing.)   
   >   
   > Okay, that explains the difference here, I think.   
      
   Um, a triangular grid _is_ hexagonal packing.  They're just different   
   ways of looking at the same arrangement, (one puts the points at cell   
   corners, the other in the cell centres).   
      
   > So, dropping the mass   
   > to 0.8g will be more than sufficient to fill in those hexagons. A   
   > further drop to 0.4g should be sufficient to ensure a hit even if the   
   > alignment of the target is "perfect".   
      
   More, smaller, projectiles doesn't solve the problem of how much mass you   
   need to throw at these speeds.   
      
   >> Remember that that spacing was if you managed to distribute things   
   >> perfectly evenly.  That isn't going to happen, I suspect that you will   
   >> get something a lot closer to a fully random distribution with all   
   >> sorts of clumps and holes.   
   >   
   > True. But now the "hail mary" is trying to find your way into one of the   
   > holes, insead of one of the clumps.   
      
   I'm not relying on slipping through a hole unless you are firing an   
   attack a couple thousand kilometres wide.  The fact that there will be   
   holes in your pattern just means that, even if you do manage to hit, you   
   might not actually hit.   
      
   To make an analogy:  In a cannon duel I'm going to try and make sure you   
   miss, but your using shells that are a dud 20% of the time isn't going to   
   help you.   
      
   >> > That said, I have already conceded a small possibility that a small   
   >> > platform could be perfectly oriented to avoid a hit. This could   
   >> > easily be remedied with slightly smaller pellets spread out more   
   >> > closely. OTOH,   
   >> > we've been talking about Hubble sized platforms, and such platforms   
   >> > are TOO SMALL to detect the small amount of energy being discussed   
   >> > here.   
   >>   
   >> Your energy assumptions are, put simply, wrong.   
   >   
   > Present your numbers.   
      
   Already done.   
      
   >> Using shot covering the same area doesn't help, it still hits the same   
   >> area.   
   >   
   > Except that 100 km is 4x the area.   
      
   You are missing the point.  You don't need 100km, you need _1000km_ or   
   more.   
      
   Your uncertainty is going to be on the order of +-1000km if not more.   
      
   > Again, this is given the extremely   
   > generous assumption that the target is going to have time to respond.   
   > Constant jinking doesn't help, either, because it always leads to a mean   
   > path, with a known degree of deviation. BTW, if you use propellant, your   
   > constant jinking will use that up very quickly. If you use a light sail,   
   > it severely reduces your range of FOV (look toward the sun and you don't   
   > get reflection, and emissions are more difficult to isolate; look away   
   > from the sun, and you get the light sail). BTW, the light sail is likely   
   > to heat your platform (unless it is angled very sharply, which will   
   > severely increase the size and mass required), meaning that it will have   
   > virtually null IR sensitivity.   
      
   I'll let you in on a little secret:  Sails can be furled, there are also   
   light sail designs other than the "parachute" often seen in SF   
   illustrations, ('wing' type sails also offer the option of simply turning   
   the whole platform side-on).   
      
   >> >> > That brings us down to 10^9 g, or 1000 tonnes.   
   >> >>   
   >> >> Which almost certainly misses entirely.   
   >> >   
   >> > Not at all, especially when you consider that a useful platform makes   
   >> > a nice, big target... especially when it is pointed at you. This is   
   >> > especially true if ou are trying to manoeuvre with a light sail.   
   >>   
   >> And we're back to ignoring time in flight.   
   >   
   > No. TIF is taken into account.   
      
   Except that you aren't, you keep trying to have it both ways:  A big   
   enough shot that you can still hit months from now but small enough to   
   actually be feasible.   
      
   A 1kt load of shot will almost certainly miss either because it is so   
   narrow as to require a perfect prediction of future manoeuvres or because   
   it is so spread out that you will have a hard time connecting with a   
   small moon.   
      
   >> When you take your shot, you have to account for _months_ of   
   >> manoeuvring blocked by the most effective concealment in the universe:   
   >> The future, (i.e. you have to account for things which haven't happened   
   >> yet).   
   >   
   > True. However, long term observation and statistics provide fairly   
   > reliable averages, as well as quite reliable standards of deviation.   
      
   Asked and answered.   
      
   You are doing the equivalent of thinking you can usefully predict the   
   result of 4d6 within 2 because you can predict 40d6 within 20 over 90% of   
   the time.   
      
      
   [continued in next message]   
      
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