From: nuny@bid.nes   
      
   On Saturday, August 13, 2016 at 7:14:34 AM UTC-7, MrAnderson wrote:   
   > Mr Fergerson, I have a design problem, it's about a truss, it's a big, heavy   
   > metal part,   
      
     The trusses we've been discussing *are* big, and they *can* be heavy, but   
   they can also be very sparse so to speak and still have the required strength.   
   They also don't *have* to be metal. If we ever get around to actually building   
   such ships I expect    
   them to be mostly built of fullerene-inspired carbon-boron-type composites   
   that are much much stronger and much much lighter than metallic alloys. Even   
   assuming such materials I also expect them to be sparely-built to keep total   
   mass down.   
      
     Incidentally, I don't know if you know this, but a truss is actually   
   stronger than a solid piece of metal of the same size and shape for the same   
   reason we have hollow bones; cracks in one place can't easily propagate   
   through the whole thing.   
      
     Therefore, the engine trusses are going be great big spiderwebby-looking   
   structures that to the eyes of somebody used to thinking in terms of steel and   
   aluminum will collapse at the first gust of wind, much less the teraNewtons of   
   thrust it will    
   actually be able to handle with ease.   
      
   > so wouldn't be better to carry whole warship on the line?   
      
     It depends, I suppose, on what you want the ship to be able to do. Trusses   
   are usually designed for loads that may change in magnitude but not in   
   direction. If your ship needs to be able to turn while under full thrust   
   that's going to unbalance the    
   load it sees at its ends and therefore the direction of the stress the rest of   
   the ship puts on the suspension point(s). That means more spars and whatnot to   
   keep it from breaking during turns, but do you really want to be maneuvering   
   smartly under full    
   thrust?.   
      
     If by "on the line" you mean a conventional rocket design with the thrusters   
   to the aft, yes, you save on material and can stack your load so that it's in   
   direct line with the thrust. On the other hand, if you do need to maneuver at   
   all while under    
   full thrust, the only feasible option is to gimbal-mount the engines. Gimbals   
   are not inherently bad things mind you- the Saturn V main stage did just fine   
   with them but it wasn't expected to operate continuously for decades, either.   
      
      
     Mark L. Fergerson   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)