Why did North Korea’s rocket launch fail?

A lot was made of the launch, but everyone quickly realized that it was all much ado about nothing.

Late last week, North Korea launched its controversial Unha-3 rocket despite heavy protests from some of the world’s largest powers, including the U.S., Britain, and Japan. After about one minute of flight, though, the 100-foot rocket exploded and its parts fell into the Yellow Sea.

North Korea’s Unha-3 rocket during in the midst of takeoff (Via: csmonitor.com)

The Unha-3, based on the TaepoDong-2 missile, was jointly developed by North Korean and Iranian rocket engineers. It was meant to fly south, to the west of the Korean peninsula between Japan and the Philippines. Upon review of its flight, experts believe that the rocket likely exploded due to severe vibrations at Max Q, or maximum dynamic air pressure.

More specifically, Max Q is the point where aerodynamic stress on the rocket as it is traveling through the atmosphere is at its greatest. The rocket created by the North Korea-Iran team was unable to throttle itself up or down to relieve said stresses and as a result, it splintered into several pieces and fell into the water below.

According to US NORTHCOM, the actual launch of the rocket lasted just a few minutes, before first stage pieces dropped into the sea about 102.5 miles west of Seoul, South Korea; the agency also reported that the missile’s other two stages failed as well, luckily with no debris falling on land.

The South Korean government estimates that their controversial neighbor to the north spent an estimated $450 million (USD) on the failed test.

The timing of the launch was meant to honor the 100th anniversary of Kim Il-sung’s birth, grandfather to Kim Jong-un, North Korea’s current dictator. There was a lot of tension surrounding the event, with many of the aforementioned countries claiming that a satellite attached to the rocket was a cover for what was clearly a long-range missile test. Their argument was that the test violated UN resolutions on nuclear and missile activity.

According to North Korea, however, the launch was meant to place a satellite into a 310-mile circular polar orbit.

The failure of the launch is made even more humiliating because of all the attention that the country had received surrounding the event itself. The government even went so far as to invite a group of foreign press to visit the launch site and missile command and control center prior to the rocket’s blastoff.

Many of those invited reported afterwards that government briefers were no longer available for comment after the rocket exploded. It is now feared that the scientists and engineers associated with the rocket will face prison sentences or death as scapegoats for the project’s failure.

It’s a lot easier to precisely control a liquid fueled rocket, plus you probably get better energy density. The advantage of solid fuel is that it is a “sealed round”, you take it off the shelf and shoot it. Liquid fuel needs maintenance and lead time to fuel. Soviet ICBMs were liquid fueled and were nightmares in terms of maintenance.

Precise control of a liquid fueled rocket is somewhat problematic, most are designed to run flat out and do not allow throttling back thrust output. They do allow cutting thrust completely but do not allow a restart. Solid fueled rockets may be controlled by employing thrust reverser's and case pressure venting.

Yes, the energy density is better with liquid fuels but when you take into account the added mass of the plumbing and turbo pumps with their own fuel supply and ancillary hardware, the actual advantage is not that much.

Your summery of the advantages/disadvantages is on the button except you left something out. The probability of failure of a mechanism is directly proportional to the number of parts making up the assembly (for want of a nail...). Yes, maintenance can help ease the problem but in the final analysis complexity is the death of reliability.

US missile technology started with solid fuel (Honest John, Pershing) moved to liquid fuel (Redstone, Atlas, Titan) and back to solid fuel (Polaris, Minuteman, and various "Standard" Missiles) with some Titan variants being hybrids with hypergolic main engines and solid boosters. Problems with hypergolic fuel led the US to go solid across the board (a dropped wrench caused a Titan to explode in it's silo and toss it's nuclear package 800 feet it the air w/no damage!).

Regards,
GtG

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