North Korea worried a lot of countries when it said it test-fired a hypersonic missile in Japan's direction North Korean state media announced Wednesday that the country has completed its second reported hypersonic weapons test. Korean Central News Agency (KCNA) said: "The test launches in the hypersonic missile sector have strategic significance in that they hasten a task for modernizing strategic armed force of the state." …
Hypersonic missiles are not only manoeuvrable and less detectable via radar than ballistic missiles, but they are also faster at around Mach 5
Are you sure about this? A ballistic missile has a terminal velocity around 5,000 m/s, that is Mach 15.
Hypersonic missiles are faster than cruise missiles.
Wikipedia confirms that a hypersonic missile goes at Mach 5.
Since you mention terminal velocity, I'm guessing that the ballistic missile attains that speed at re-entry. By definition, a ballistic trajectory has a high point. Before that point, it's going up, after that point, it's going down. Only when going down can it increase its speed, and it can only increase its speed while the atmosphere is not thick enough to slow it down.
Pretty much that, ICBM warheads are travelling at around Mach-25 just before re-entry and then slow rapidly as they decend to the target, these missiles are doing Mach-5 plus at very high altitude and also slow down in the final flight stage, not much can exceed Mach-3 for long at lower levels, especially not a glider.
'Hypersonic missiles' are being touted as the new global threat, one of those made up titles used to impress non engineers at budget time. The Russian KH22* anti ship cruise missile (operational since the 1960s) can manage well over Mach-4 during its mid flight phase, these are just faster and longer ranged. The response will be also be faster longer ranged missiles.
*A Major driver in developing the F14 & AIM54 system.
You are counting only radial component of velocity: you must also take into account tangential. We know by reading Wikipedia that ballistic missile can reach targets within about 10,000km in about 30m or 1,800s, giving average speed over the ground of around 5,555 m/s. Actual average tangential component of velocity will be higher as missile takes much longer path of course. This gives average speed over ground of ballistic missile of approx mach 15.
I don't want to defend the North Koreans, but I wonder whether a rocket that flies / glides towards its target can be called a ballistic missile? The dictionary definition of a ballistic missile seems to be:
"a missile with a high, arching trajectory, which is initially powered and guided but falls under gravity on to its target."
The statement from South Korea's Ministry of Foreign Affairs, that "the North is also banned from making any launch using ballistic missile technology" sounds very much like an attempt to associate a squared peg with a round hole. We always consider the West as the straight negotiators, dealing with duplicitous North Koreans. But sometimes I feel that the Western powers are quite liberal in interpreting the rules. Not an approach that will endear you to the other side when it comes to the next set of negotiations.
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