The Mainichi Shimbun answers some common questions readers may have about the latest nuclear warhead test that North Korea says it has successfully conducted.
Question: What is a nuclear warhead?
Answer: It's a nuclear weapon attached atop a missile. A nuclear missile, therefore, refers to a missile carrying a nuclear warhead. North Korea has also been conducting missile launch tests since the beginning of the year. Based on the technology of the former Soviet Union's Scud ballistic missile series, Pyongyang has developed Nodong and Taepodong missiles, and in June this year it successfully launched a new line of intermediate-range ballistic missiles called Musudan and then an "SLBM" (submarine-launched ballistic missile) in August.
The Nodong and Musudan are said to have a firing range wide enough to cover Japan and the improved model of the Taepodong-2 is believed to be able to reach the U.S. mainland. North Korea appears to be trying to display its capacity to attack with nuclear missiles.
Q: What is North Korea's aim with repeated nuclear testing?
A: Nuclear weapons need to be small in order to be carried on missiles. By repeating nuclear tests, North Korea is probably assessing data to see if the nuclear fusion can be initiated while acquiring nuclear control technology. The Soviet Union successfully miniaturized nuclear weapons after conducting four tests over a span of four years, while China created smaller nuclear warheads over two years through three tests. North Korea has recently conducted its fifth test.
Q: Will North Korea's success in miniaturizing nuclear warheads mean it'll have a terrifying weapon?
A: Not necessarily. Long-range ballistic missiles ascend and leave the atmosphere before falling back to Earth in a parabolic motion. When a missile makes a re-entry into the atmosphere, its tip is exposed to high-temperature heat due to friction. Missiles will need to have the strength and design that would endure such high heat. While North Korea announced in March that it successfully conducted atmospheric re-entry simulation, some experts doubt Pyongyang's claim, saying that it still has old-fashioned warheads and they doubt whether the weapons could survive the heat. (Answers by Naritake Machida, Tokyo City News Department)