From: nuny@bid.nes   
      
   On Tuesday, July 19, 2016 at 2:26:45 PM UTC-7, MrAnderson wrote:   
   > Yes, just like this, but more like Valkyrie Antimatter Starship or Avatar ISV   
   > Venture Star, check them out on Atomic Rockets, they are both in STL   
   > Starships section.   
      
     Okay, so much much larger than the Revell ship, and a kilometer or so of   
   rigid truss designed to support its load in tension instead of one or more   
   cables, but still the same principle. Got it.   
      
   > In real life the propulsion module would be much more distant from the   
   > habitat, and thrust would be projected in a little angle, so you doesn't   
   > loose a lot of power, but you doesn't burn your face.   
      
     In my opinion the loss of power from angling the thrusters outward is being   
   wrongly handwaved away. For a long interstellar voyage every little bit of   
   inefficiency runs up your fuel budget greatly even if you can make the Bussard   
   concept work to    
   collect fuel along the way. You can't collect *antimatter* along the way.   
      
     Also consider that the support structure between the thrusters will be under   
   a hell of a lot of compression. That's a really bad place for a structural   
   failure in mid-trip, as bad as failure in the tow truss.   
      
     I'm thinking more of a hammerhead arrangement with the thrusters out on   
   booms so the thrust can be directed exactly rearward- the leading edges of the   
   booms  would also be under compression and the trailing edge under tension but   
   there's a lot more    
   room for more material to take the stresses. It would increase total ship mass   
   by a few percent but also be much stronger and put all of the thrust where   
   it'll do the most good.   
       
   > About a safety... I don't think 4 cables would change this that much. With   
   > one made of nanotubes with protective layer of something you got strong,   
   > light and safe line.   
      
     I believe that to be more handwaving. The nanotube part is OK, we're getting   
   close to making that sort of thing today, but think about what that protective   
   layer has to protect against- intense ionizing radiation, extreme heat, and   
   the usual    
   micrometeorites and dust at high relative velocity. The lines *will* stretch   
   under load- if the coating doesn't have *exactly* the same coefficient of   
   stretch it'll eventually crack and the protection fails, then the cable fails.   
   Redundancy is a Good    
   Thing.   
      
   > If you break one of four cables you are in trouble anyway.   
      
     Well, not really- with one of four cables broken you have three-fourths of   
   the load-carrying capacity but the system has to be overdesigned in case of   
   needing greater-than-normal thrust in emergencies, and with one broken the   
   line of thrust is still in    
   the same line. Best case you shut down thrust, reel everything in, and repair   
   or replace the broken cable. Worst case your margin for emergency thrust is   
   reduced. Breaking two cables would be as catastrophic as breaking the only   
   cable on a one-cable    
   setup.   
      
     A solid truss structure makes all of that more or less moot though.   
      
   > And with starting the rocket, in my applications, the cable is already   
   > expanded, so just turn AMAT rocket and go!   
      
     With a solid truss, yes, but cables?   
      
   > So, it seems that manevuering is easy part with waterskiing spacecrafts ;)   
      
     Cables, yes. The only issue with a single cable is making sure the   
   attachment point at the thrust module can handle some lateral movement, frinst   
   using a ball and socket.   
      
     The rigid tension truss will distribute lateral force over its length so it   
   has to have some ability to bend, but not too much. The part on the outside of   
   a turn will feel more tension than usual while the part on the inside will   
   feel less. But then,    
   there won't be many turns during an interstellar cruise.   
      
   > I also think about exchangable cargo modules. It makes interesting   
   > opportunities for space warfare, exploration, and stuff like that. First,   
   > Antimatter is dangerous. With towing part placed on orbit of sun, you detach   
   > cargo part, and fly to targeted planet by fusion or anything else (keep in   
   > mind I talk about interstellar rocket here).   
      
     Yeah, landing and launching interstellar antimatter rockets are Bad Ideas.   
      
     Plus, as pointed out elsewhere, making antimatter is energy-expensive so   
   you'll want your antimatter factory close to a star. Which reminds me- for   
   first trips to other stars you'll need to take such a factory along if you   
   can't carry enough for a    
   return trip. Might as well park it near the star where there's plenty of   
   energy available for free. In a combat situation you'll probably want to try   
   to capture the enemy's antimatter plant assuming they have one.   
      
   > And for combat spaceships, place tug in outer part of system, and then fly   
   > with small, easy to manevuer craft to battle area. Mr. Winchell Chung on   
   > Atomic Rockets said that space warships probably won't be waterskiing, as   
   > this construction is too fragile (or something like that, I don't remember   
   > exactly). With my concept, you bypass that.    
   > What do you think?   
      
     So, a sort of scaled-up version of the Jedi Starfighters in Star Wars,   
   replacing the Hyperdrive Rings with an antimatter rocket?   
      
     I'd be tempted to make the engine module/truss/crew module assembly as a   
   sort of bus that stays connected at all times, with the combat craft attached   
   along the truss. The combat craft won't be accessible under thrust because of   
   radiation and whatnot,    
   so you'd need to get almost within combat range, then shut down the main drive   
   so you can send the crews to their craft for launch.   
      
     The interstellar bus can be left on a trajectory that carries it past the   
   planned battle space for recovery of the combat craft or just parked where the   
   enemy won't be able to reach it. I think we're both assuming built-in point   
   defenses against long-   
   range missiles and such.   
      
     Now that I think about it, the interstellar ship will be running tail-first   
   into the target system so as to shed its relatively large interstellar travel   
   velocity. You won't want to shed all of it so the launched combat craft can   
   take advantage of some    
   of that velocity to increase their range without burning fuel. They'd be   
   mechanically ejected stern-first from the bus, then boost to *slow* into   
   combat range with the enemy. Afterward the bus finishes decelerating and/or   
   finds a convenient place to park    
   or orbit so the combat ships can be recovered.   
      
      
   [continued in next message]   
      
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