Le jeudi 29 septembre 2016 16:36:30 UTC+2, Mikkel Haaheim a écrit :   
      
   > First, I think you mean "expEndable".   
      
   Oops...   
      
   > Second, what you are describing is essentially the multi-stage heat sink   
   being discussed.   
      
   Oh, I had understood that in the multi-stage heat sink, the heat sink itself   
   was immobile, with inner parts hotter than outer parts, and components of   
   varied working temperature there.   
   Thinking about it, I don't really see how it could work well.   
      
   > Third, you have to be somewhat careful with your use of multi-stage heat   
   sinks. On the one hand, as mentioned, there are some things that have very   
   narrow ranges of temperature tolerance. If the initial coolant temp is too   
   cold, they freeze, and don't    
   work. If the initial coolant temperature is too hot, they overheat, and don't   
   work. Sometimes the difference is on the order of tens of degrees, or even   
   less. Conversely, some things require extremely cold coolant, which they   
   quickly heat to very high    
   temperatures. What this means is that you can not just sequence the things   
   that need to get cooled... you also need to run some of the coolant flows in   
   parallel.   
      
   Yes, it would definitively be an engineering challenge, but by controlling   
   flow volume and speed, how significantly more difficult would it make the   
   design to build?   
      
   > > > How much of that impact mass will be from unused hydrogen fuel?   
   > >    
   > > Ideally none or a small margin: hydrogen that was not used is wasted.   
   Either the craft itself could have been smaller, or it could have been   
   replaced with a deadlier payload.   
   >    
   > OTOH, the H2 makes a very nice explosive. Remaining H2 would allow for a   
   mission reserve in case of fluid loss, and reacts vigourously with a large   
   variety of oxidisers. This actually adds to the argument for having a closed   
   H2 loop.   
      
   Compared to its kinetic energy, the oxidation energy won't make much of a   
   difference. Would it have secondary effects in addition to pure energy effect?   
      
   Hydrogen loop would require moving around solid hydrogen, which would make   
   things... complicated.   
      
   While we're at it, how would a solid thermal superconductor work for the loop?   
   As we are around 3K, superconductors should be easier to come by.   
      
   > > But if you mass-produce those or are not sure of the target as you build   
   them, hydrogen will carry kinetic energy as well. If it is solid, it may even   
   work as decent shrapnel, otherwise it is limited to full-tank-sized shrapnel   
   fragment.   
   >    
   > Solid H2 would act very poorly as shrapnel. The low density would give it   
   about as much shrapnel potential as a very soft snowball... in hell,   
   considering its extremely low melting point.   
      
   For what I understand, at interplanetary speeds, hardness becomes irrelevant   
   as objects don't have time to crumple, and a very soft snowball will hit as   
   hard as a tungsten coin. A very large, thin tungsten coin hitting face-on.   
      
      
   > > I wouldn't hit one farm or atmosphere generator - I would hit all of them.   
   Similarly to an ICBM attack, launch a multitude of those and put MIRVs on   
   them, optionally with a few nukes if you need the extra punch. With that, you   
   can blanket several    
   areas with the fists of God. This should be enough to kill most of everyone   
   and wreck any concerted terraforming effort below the 'robust planet-wide   
   self-sustaining ecosystem' or 'breathable atmosphere' phases.   
   >    
   > I would point out that if a multitude of projectiles are required to do the   
   damage, it no longer qualifies as a WMD (nor a "world killer". That said, I   
   agree that a KKV can be used as a WMD if it is detonated before impact, and   
   therefor spreads the    
   impact over a large area. I am less confident that such attacks will hit   
   everything, unless ou launch multiple salvos several hours apart. The high   
   relative velocity pretty much means that you can only hit one side of a planet   
   or moon, which means you    
   will need to time at least one other volley to impact when the other side   
   rotates into position. Even then, if we are talking about a large moon or   
   planet, especially with assets spread throughout orbit, it will be very   
   difficult for even hundreds of    
   such weapons to hit all the targets.   
      
   Sorry, by world-killer I meant the launcher itself, which is capable of   
   launching a whole slew of those. An individual craft is a 'world-killer' in   
   the context of space stations, habitats and inhabited small asteroids as   
   worlds.   
   I think I've read a weapon described that way in Schismatrix.   
      
   By the way, you have convinced me that a water design would probably be better   
   adapted for this particular use: less dV is needed as the initial covert   
   launch gives a good acceleration, more autonomy means that it can take more   
   time to arrive (which also    
   help for coordinated strikes) and the simpler design will cope better with   
   such acceleration.   
      
   > > > Consider how the "Greek camp" and "Trojan camp" of Trojan asteroids are    
   > > actually closer to Earth, (in terms of travel time, physical distance is    
   > > about the same), than they are to Jupiter even though they are out in    
   > > Jupiter's orbit.    
   > >    
   > > Indeed, and this was something I had never realized until Zane Markowsky's   
   Chidren of a Dead Earth(*) pointed it out: to one part of the Belt, the inner   
   planets are closer than other parts, travel-wise.   
   > > He describes how coherent polities form based on asteroid families (that   
   are relatively close to each-other), instead of a 'Belt culture'.   
   > > Orbital mechanics are a funny thing.   
   > >    
   >    
      
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