Rentry Vehicle Design--How hard is it? (Somewhat long)

Factual Questions
1

According to this story, a US official claims that North Korea now has the ability to launch nuclear weapons at the US.

I find this to less than credible for the following reasons:

  1. They have not launched a single Taepo Dong 2. As far as I know, this is the only rocket that would have the capability to launch a miniaturize warhead (estimated to be 1300 lbs.). And you would need several flights to ensure that you’ve got all of the bugs out. No point in lashing a nuke on the tip, if there’s a good chance you would loose the rocket in flight.

  2. To be able to launch a usable nuclear weapon into a ballistic trajectory requires mininaturization. Your Fat Man type bomb just isn’t practical for use on an ICBM. For one thing it’s big and heavy. Your going to need to rent a Big U-Haul to lug it around for something that weighs about 3 to 4 tons. Which of course requires a big rocket. The Taepo Dong 2 isn’t design for that kind of load. It’ll carry maybe 1500 lbs. tops for a special delievery to the US. So you need to shrink it. And test it. And test it again. Even if you had Los Alamos codes, you’re still going to need to validate the design. I have not heard of any above ground or under ground testing in NK. Yet…

  3. They have yet to demostrate that they’ve built a robust Re-entry Vehicle that can survive the descent to the target. One only has to look at the footage of RV’s smacking into the lagoon in Kajawline [sic] to understand that we’re talking serious heat.

Which brings me to this question… How easy or hard is it to make an RV? What materials do you use and where do get them? How expensive is it and how do you test the design? Does NK have the technical resources to pull this off? I seem to recall that Alaska spruce is used in making part of the RV. Or did “Father of the Pakastani Bomb” Khan spill the beans on this too?

2

IANAE, but you have to remember that the technology to shield something on reentry is over 40 years old, and it really doesn’t have to be all that sophisticated (unlike a nuke). The Apollo capsules used a honeycomb impregnated with a resin which burned off at a controlled rate during reentry. By doing so, it carried the heat away from the capsule, so all you really need to know is how fast something’s going to be coming into the atmosphere (pretty easy to figure out) the cross section of it that’s going to be exposed to the heat of reentry (again, pretty easy to figure out), how long it’s going to be “cooked” (again, ah hell, you know), then it’s a simple matter of figuring out a material which will burn away at the desired rate. A warhead’s actually going to be easier to shield than a capsule containing humans, since you can design electronics to survive greater temperature extremes than human beings can.

3

India figured it out a while back. It’s certainly much easier than making a miniaturized nuke.

4

The Avco Everett Research Labs were founded precisely to answer this question (Arthur Kantrowitz’ work on shock tubes allowed a lot of testing to be done on the ground, rather than with expensive and time-consuming missile shots). There used to be a plaque bolted to the wall that showed experimental vs. theoretical predictions of ablation of the re-entry surface. see here, too, for som,e background:

http://www.aerowebspace.com/Sutton.shtml

Of course, with a lot of research declassified and easily accessible, and with extremely easy computer simulations now possible, anyone starting on the problem todaty has a considerable head start over anyone striking out in virgin territory in the 1950s.