From: nuny@bid.nes   
      
   On Friday, September 30, 2016 at 8:07:22 AM UTC-7, elie....@gmail.com wrote:   
   > Le vendredi 30 septembre 2016 03:57:11 UTC+2, nu...@bid.nes a écrit :   
   > > On Thursday, September 29, 2016 at 3:20:46 AM UTC-7, elie....@gmail.com   
   wrote:   
   > > > > > Bulk is a drawback, but not such a big one I suspect. By far the most   
   > > > > > energy received is from the Sun, and this is taken care of with the   
   > > > > > solar-thermal engine. For the rest, you end up with a long, thin   
   cone,   
   > > > > > but this craft doesn't have to manoeuvre anyway.    
   > > >    
   > > > > Why not? You cannot aim your launches from several AU away to guarantee   
   > > > > a hit without course corrections just from stray gusts of solar wind,   
   > > > > never mind magnetic and gravitational perturbations or enemy action.   
   > > >    
   > > > I meant high-thrust manoeuvres, like a chemical or even nuclear rocket   
   > > > would give. It already has manoeuvring capabilities akin to a ion drive.   
   > > > But the minimal acceleration allows for the less thrust-optimised shape   
   > > > of a long, thin cone.   
   > >    
   > >   Remember you're constantly accelerating to get maximum bang on impact and   
   > > to minimize chance of interception. That means you're going to build   
   > > velocity rather more quickly than today's burn-a-little-then-coast-a-lot   
   > > space travel. You're going to need a lot of lateral deltavee to do even the   
   > > most minor course corrections the closer you get to a target, especially   
   > > for precision targeting like bunker-busting.   
   > >    
   > >   Your assumption that the spaceframe only needs to handle lengthwise   
   > > thrust needs re-examining. Below you mention a point that makes it worse,   
   > > turnaround before impact. I think turnaround is a very bad idea, and I'll   
   > > go into why below.   
   >    
   > It is constantly accelerating in an arbitrary direction, but at extremely low   
   > accelerations - micro-g or probably less. This is not quite freefall, but you   
   > can have some pretty outlandish designs with that as a constraint.   
      
     Yes, I get that, but that's not the sole constraint. My point is that the   
   closer to the target you get, the faster you're traveling WRT it. That ramps   
   up the needed lateral deltavee for course corrections in a constantly   
   shrinking amount of time, hence    
   greater lateral accelerations (and torques, depending on how the deltavee is   
   applied, meaning where the RCS thrusters are placed) the spaceframe has to be   
   able to tolerate.   
      
   > The idea is that you already know where the target is - probably a fixed   
   > installation (including orbital stations), so the entire trajectory can be   
   > calculated in advance. It would include some astrogation system, for example   
   > tiny sensors locked on a few bright stars, planets and (obviously) the Sun,   
   > for course-correction, but those can be incredibly small.   
      
     You're also talking travel times of at least months for all of those   
   independent looping trajectories to converge. In that time your targets can   
   *move* for any number of reasons like natural disasters screwing up their   
   roads or other supply routes,    
   technological innovations, and so on. For that matter, their whole defensive   
   posture may have changed for political or other reasons, meaning the defenses   
   you targeted aren't there any more, and the command centers might get moved to   
   another state.    
   Suppose they build stuff you don't know about.   
      
     Example- Cheyenne Mountain used to be the command center for the US nuclear   
   defense command, but with the advent of exactly the kind of nuke   
   bunker-nusters you describe, it got moved, and where to is a secret. The   
   Soviets and Chinese did the same thing.   
      
     How good is your spy system? Your enemy likely won't be announcing this   
   stuff in the newspapers.   
      
     Why are you assuming their spying efforts aren't equal to yours, and they   
   can't know exactly where your missile production lines are located and their   
   schedules? Why do you assume they don't know when you're moving them en masse   
   to the launchers?    
   Remember the Cuban missile crisis?   
      
   > The point of a stealth system is that the target doesn't see it coming, and   
   > thus won't be able to take counter-measures like moving a station out of the   
   > way.   
   > Even if the terminal phase imply detection (ideally it shouldn't), this   
   > should be short enough that no meaningful counter-measure can be taken,   
   > including shooting it down.   
      
     Yes, I got that. But as I said, once they're detected (say during turnaround   
   a million km out) all that needs to be done is to place any solid matter in   
   its path before it hits the target, causing it to expend most of its momentum   
   shattering itself    
   into less-damaging pieces.   
      
     I don't consider high-altitude hypersonic interceptors flown by suicide   
   pilots unbelievable in a scenario that assumes massive intentional civilian   
   deaths.   
      
     What about observation platforms stationed at the Lagrange points of planets   
   they control? They don't stand still, they have to do little kidney-shaped   
   orbits around those points, making continuous corrections because those little   
   orbits are chaotic.    
   They'll be nearly impossible to hit.   
      
   > As for vertical acceleration, this is only for the catapult launch. This   
   > would have tremendous acceleration for a very short time.   
      
     Yes. You are still trying to pretend late-phase large lateral accelerations   
   will never be needed, but they will especially for turnaround.   
      
   > > > > I mentioned earlier that there will be components you can't allow to   
   get   
   > > > > very cold at any time or that have a significant required warmup time,   
   > > > > so they can be buried in the warmer parts of the heat sink.    
   > > >    
   > > > > OTOH having different parts of it at different temps may also be   
   > > > > problematic, if it's even possible. A multi-stage heat sink arrangement   
   > > > > could mitigate that at the expense of more tankage and plumbing.   
   > > >    
   > > > With expandable coolant like here, (as described above), I would use the   
   > > > opposite design: use the expandable coolant to first cool the coldest   
   > > > parts, then the warmer ones in order. This way, it is always colder than   
   > > > what it is supposed to cool down, until the solar-thermal drive part   
   > > > where it is heated up to possibly thousands of K.   
   > >    
   > > (Include correction of "expandable" to "expendable"- I wondered about that   
   > > too)   
   > >    
   > >   Simple is good but that's too simplistic to work. Just because a   
      
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