Read and watch more about North Korea in "March Madness," a VICE News special section on the Hermit Kingdom.
North Korea is merrily chugging along in its quest to develop rocket engines for long-range missiles that could one day send a nuclear weapon across the world, according to recent reports indicating that Kim Jong-un's regime had successfully tested a solid-fuel rocket motor.
The news, which comes during the heightened regional tensions that typically accompany annual military exercises between the US and South Korea held in March, raises several questions, such as "Why?" "So?" and "Does anyone care?"
The short of it is that solid rocket motors are better suited for military ballistic applications than liquid propellants. The North's test is likely a long-term development that it has made a point of advertising in the wake of its fourth nuclear test in January and a ballistic missile launch in February.
But for the deeper dive, let's start with rocket motors. If you're in the fun and exciting business of riding explosions for lift, as all rockets do, there are many different ways to talk propulsion. One big way is to classify a rocket based by the type of fuel it uses — a liquid or solid propellant.
Liquid propellants tend to involve liquefied gases and hydrocarbon fuel. Solid propellants are, basically, explosives. The very first ancient rockets used gunpowder as a solid fuel, while the liquid rocket engine shares some design traits with jet and automobile engines.
As you might expect, this results in very different kinds of design. A rocket engine that burns liquid fuel involves lots of plumbing and fine-tuning. It's easier to build, but also more complex and harder to use.
Solid-fuel motors are almost the exact opposite. They're incredibly unforgiving of manufacturing flaws, extraordinarily simple in design, and very, very easy to use. The motor is pretty much an explosion in a can — dead simple in concept, dead easy to screw up in practice.
Encyclopedia Astronautica lays out the following breakdown of the advantages and disadvantages of solid propellant.
Advantages of solid rocket motors, many of which make them ideal for military applications:
1. High density and low volume.
2. Nearly indefinite storage life.
3. Instant ignition without fueling operations.
4. High reliability.
The disadvantages of solid propellants include:
1. Slightly higher empty mass for the rocket stage.
2. Slightly lower performance than storable liquid propellants.
3. Transportability issues: Solid propellants are cast into the motor in the factory, unlike liquid fuel rockets which can be fueled at the launch pad. This means they have to either be: 1) limited in size to be transportable; 2) cast in segments, with the segments assembled at the launch base; or 3) cast in a factory at the launch site.
4. Once ignited, solid motors cannot be easily shut down or throttled. Thereafter they have to be rebuilt for a specific mission.
5. Nearly always catastrophic results in the event of a failure.
To think about it another way, liquid propellant engines are everything a true-blue gearhead wants and needs: lots of things to fiddle with and adjust. Solid propellant motors are the kind of rocket engine you might give to your grandma, a small child, or a drunk to operate.
When it comes to all the horrible things that regularly go awry in a war, it isn't a surprise that the sheer amount of "no muss, no fuss" that goes with solid propellants makes them real champs. The US used liquid propellant with all of its original intercontinental nuclear missiles, but switched to solid fuel later on.
If that's the case, you might wonder what's taken North Korea so long to do this. I mean, there's got to be some instructions somewhere on wikiHow or whatever, right?
North Korea makes a couple of short-range missiles that use solid fuel, but small solid rocket motors and massive solid rocket motors are two very different ballgames. The design, pouring, and casting of large motors are quite difficult, perhaps even reaching official "dark art" status.
The solid rocket propellant provides a great deal of the structural integrity of the rocket, which means that it's carrying and distributing a load while it's on fire. Always tricky.
It's not much of an exaggeration to say that any rocket that uses solid propellants and works means that the rocket motor was built flawlessly. Anything less and you've got large rocket blowing a whole lot of firepower and equipment all over creation. From a user's perspective, a solid-fuel motor is like a super-big bottle rocket, while a liquid-fuel engine on a rocket is closer to a machine shop or chemistry lab project.
The solid fuel development comes together with the other tests and demonstrations North Korea has been on about in recent weeks. The rogue nation appears to be working through technical issues in several areas: the development of a road-mobile missile, the KN-08; a submarine-launched ballistic missile; and solid-fuel rocket engines (with a side focus on miniaturized nuclear warheads).
The KN-08 and the submarine-launched missile are both complex missile technologies that rely on liquid-propellant engines. Both are systems that could (in theory) hide through or ride out an initial US strike on North Korean military installations. But when they're getting ready to launch, they require all that pain-in-the-ass fueling rigmarole and last-minute tweaking nonsense typical of liquid-fueled rockets.
Even if the North Koreans were able to master solid propulsion tomorrow, it's practically impossible to swap out a liquid propellant engine for a solid rocket motor because, well, rocket science. If you make one major change on a rocket, it affects everything else. You end up basically having to redesign the rocket.
Nevertheless, if and when the country is able to pull these different threads together, probably within the next several years, it'll have a stable of not-half-bad strategic nuclear weapons.
The reason they've been visibly fussing about it this week is to make a virtue of a necessity. They have to do some tests anyway, so running them now nets the North Koreans a nice little saber-rattling bonus to go with their improving grasp of technology.
Follow Ryan Faith on Twitter: @Operation_Ryan