The second test of a North Korean intercontinental ballistic missile (ICBM) has elevated concerns over the potential for this nation to launch nuclear strikes on the continental United States. Several major cities are in range. There has been some boffin speculation on the accuracy of North Korea’s ICBMs, but even a relatively inaccurate weapon could still be effective. The US is filled with large urban sprawl conurbations that present very large targets for ICBM attacks. A missile doesn’t have to land exactly in downtown to cause massive casualties.

Friday's test seems to be a souped-up version of the missile tested in early July, probably with a larger upper stage. This accounts for the longer range and flight time of the latest launch.

While the range of this missile is concerning, an equally relevant question is its reliability. North Korea has now conducted two successful tests of this ICBM, in addition to earlier successfully testing its re-entry vehicle (warhead). That supports the idea that the missile is probably debugged. But another clue is the timing. North Korea has conducted two launches of this advanced system in less than a month.

Political factors seem to have influenced the timing of the launches, and weather problems apparently produced a slight delay in the second test. US Independence Day, 4 July, was the date of the first launch, and the second launch seems to have been originally slated for the anniversary of the Korean armistice on Thursday. Take away these influences, and North Korea could have conceivably conducted both launches in an even shorter time interval.

The 4 July launch would have been studied closely by engineers. Telemetry from the missile, as well as photography and tracking data, would all have been scrutinised. Such analyses take time, especially if problems of any sort are detected. If something goes wrong, it takes even longer to diagnose the cause of the trouble, and more time to make corrections for the next launch. Such events usually occur over a period of months.

The fact that preparations for another missile launch were completed in less than a month gives insight into what has happened behind closed doors. The first launch was presumably judged to be successful. No fault diagnoses were required. No corrections needed to be made to the design or manufacturing of the next missile, apart from adding an improved second stage. This stage was probably waiting, already assembled in the wings before the first test. All that needed to be done was to wait for orders to launch at a politically auspicious moment.

More tests of this missile could be performed in the near future. But the success of two tests in a row, with no launch failures and a successful maiden launch, is uncommon in rocketry. North Korea is notorious for its bellicose rhetoric against America, which has typically fallen well short of the nation’s true military potential. The rapid progress of the ICBM program suggests reality is catching up with the rhetoric.