High resolution photographs are an amazing feature of our modern era. When North Korea holds a militayr parade, we get amazing photographs that show all kinds of details. And a lot of us noticed one partiuclar detail about the airframes of North Korea's Pukguksong submarine launched ballistic missile. They surface detail looks like a wound filament.
So what? One thing hold back North Korea's missile program is how much the airframes weigh. The debris we have seen from North Korean space launches shows that the airframe is a pretty basic -- and therefore heavy -- metal structure. As my colleague Michael Duitsman points out, a wound-filament casing makes the possibility of a sold-fueled ICBM far more credible.
The fundamental issue with solid-fueled motors is making a case strong enough to withstand the pressure of the burning fuel powering the rocket and light enough to fly. This is precisely why the Germans went with liquid-fuels during the Second World War -- existing metallurgy and explosives could get a rocket of any size off the ground.
Wound-filament helps solve this problem, offering a light-weight but strong structure.
Until now, all of North KOrea's rockets had simple metal airframes.
North Korea showed two canisters for a future ICBM at the most recent parade. One question is: Can North Korea make a solid-fueled ICBM that would fit inside either canister. And the short answer is: Not with a simple metal airframe. It would be too heavy.
There is also the issue of the canister. Remember, the challenge is not just making a missile that can carry a nuclear weapon to the United States -- it is to make an operational mobile missile that can evade efforts by the United States to find and destory it prior to launch.
The big-take away is that wound-filament airframes would be a significant -- and necessary -- advance for North Korea to make if it wanted to develop a solid-fueled ICBM.