A few days ago, one of my students was asking me about the North Korean Taepodong-2 Missile that has been in the news so much lately. So, that makes them think that I know anything about missiles? Well, I guess that I do know a bit, but still …

Anyway, I thought that I might do another break with my normal posts and say a few things about the Taepodong missile. After all, I’ve done Atlas rockets and Delta rockets here, and I have plans to do Redstone and Titan rockets sometime in the future. However, those rockets are used in space exploration, so they sort of fit with my blog. But, rockets are rockets. When they launch, it makes no difference whether they are putting something into orbit or placing a payload into a suborbital trajectory. What makes the difference between a missile and a rocket is whether or not the payload is a warhead. The vehicle works the same way.

So, on to the North Korean missile. The Taepodong-2 missile strikes me as rather inferior technology to the missiles deployed by most nations. Of course, if the warhead is falling on you, then you don’t really care how sophisticated the missile that put it there might be. The Taepodong-2 seems to be basically two missiles stacked on top of each other. The first stage appears to be heavily based upon China’s CSS-2 missile (a very old, not very efficient, but sturdy design). Stacked on top of the first stage is what appears to be a North Korean No-Dong missile, or something that is merely a modification of one. As with many Russian or Chinese designs, the upper stage is supported by a truss type structure above the lower stage. Most American missiles at least cover such support structures with farings or cowlings. This is supposed to improve aerodynamics, and gives a much more aesthetic look to the rocket. Also, enclosing the structure keeps wildlife from trying to nest in the rocket prior to launch (a problem when launching from Florida). Simply stacking rockets, though the basic idea behind staging, is not as efficient as designing specific stages to fit seamlessly with the booster. This inefficiency could significantly reduce the performance and range of the Taepodong-2 below the figures often bandied about. A solid fueled third stage is believed to be capable of being fitted on top of the second stage. This would give either greater range or greater payload capability. The maximum anticipated range is in the neighborhood of 9000 km. This permits a warhead delivery nearly 3/4 way around the world from North Korea (Oops.  As a reader pointed out, this should be halfway around the world, not 3/4.  Sorry about that.). Both first and second stages are believed fitted with inertial guidance. Earlier versions steered using four steering vanes in the rocket’s exhaust gasses. Later versions are believed to possibly have gimbaled vernier rocket nozzles which can be used to steer. This is a more reliable technique if it works, but far more difficult to implement. Accuracy of the Taepodong-2 rocket is believed to be poor, particularly as the target range increases. At extreme range, it would probably be lucky if the rocket landed close enough to its designated target to do any damage at all, even with a nuclear warhead.

Both the first and second stages of the Taepodong-2 rocket use liquid storable propellants. The fuel is TM-185, a mixture of 80% kerosene and 20% gasoline. The oxidizer is AK-271, a mixture of 73% nitric acid (HNO₃) and 27% dinitrogen textroxide (N₂O₄). These are considered storable propellants because they can sit in the tanks for a while between fueling and launching the rocket, unlike cryogenic fluids such as liquid hydrogen or liquid oxygen. However, these fluids, particularly the oxidizer, are very corrosive and dangerous to handle. Rocket tanks are designed to be as light as possible in order to maximize payload capability (what good is a rocket if all it can do is lift itself off the ground but not carry anything else?). These lightweight tanks, though, are more susceptible to corrosion than heavier storage tanks. According to some reports, the tanks begin to corrode within 24 hours of fueling. So, fueling, removing fuel, and refueling runs a significant risk of increasing the possibility of a launch failure. That means that once fueled, the rocket is generally committed to fly. The corrosive nature of the fuel also means that firing the engines basically wears them out. They need to be rebuilt after firing. Thus, the engines aboard the rocket have never actually been tested. Engines just like them have been tested, but not those particular engines. So, there will always be a question as to how they will actually function in real usage. Thus, though the propellant is “storable”, that merely means that the rocket can be fueled and then held for up to a month or so before firing. The launch facility for the Taepodong rockets is a typical launch pad. This is a surface facility, with gantry and the like. This makes the entire assembly and fueling procedure visible to surveillance. Furthermore, such a facility limits the launches to one missile at a time, and even then only in fair weather. The Taepodong missiles probably can not be launched in the winter months due to poor weather. A surface launch facility is also subject to air raid, and even a very limited air raid would render the launch facility useless for future launches. Such limitations severely restrict the strategic military capabilities of the missile. This is clearly not a first strike weapon, nor is it a particularly good deterrent type missile. At best, though classified as an ICBM (Intercontinental Ballistic Missile), it is really a terrorist weapon.

The warhead payload of the Taepodong-2 is believed to be in the 500kg to 750kg range. Such a payload could allow the missile to carry a fairly large conventional warhead, but the poor accuracy of the missile would make such a warhead totally ineffective. While a nuclear warhead can be fabricated to that mass specification, it is difficult. Nuclear weapons, particularly fission weapons, are not difficult to make. Any second year physics student knows the basic theory. However, getting the raw material is much more difficult. This is where the bottleneck comes in. North Korea may have overcome this problem, and sufficiently enriched fissionable material is likely to be in their hands. However, while making a fission device that will explode isn’t so tough, making a small and high efficiency one is difficult. While it may be possible for North Korea to make nuclear weapons, it is much harder to make them light enough and small enough to fit on top of a Taepodong missile. I would think it unlikely that they have that technology at this time. Without a nuclear warhead, though, the Taepodong missile is very little threat other than to peace of mind. At best, they could fire one missile, which would likely miss the target and simply blow a hole if some farmer’s field somewhere. The international response would be immediate and decisive. North Korea would then be unable to launch any more missiles from its sole launch facility.

The Taepodong-2 missile limitations reminds me a bit of the Soviet R-7 missile. This rocket was also billed as an ICBM, but it could not be fueled and left to sit around, it took nearly a day to prepare, could only be launched from select locations, and could not be housed in silos. The R-7 missile, though, became the basis for almost all Soviet and Russian space launches, evolving into the Soyuz rocket. The Taepodong-2 is a very poor missile for military purposes. However, with a third stage fitted, the Taepodong-2 may be capable of lifting a satellite of 100kg to 500kg mass into orbit. Personally, I’d consider this a far better use for the rocket, anyway.

-Astroprof