The Korea Herald reported on Apr 28, 2021 that the South Korean Defense Minister had commented on a recent test flight of North Korean missiles.
He was reported to have said that the missile flew 600 km by the “pull-up” method. That was a revision of an earlier statement that the missile flew 450km. So naturally, I wanted to know what this method is.
It turns out it is a way of using the atmosphere and the region above the atmosphere. It is rather like skimming a stone across the water on a lake.
In a normal flight, a missile follows a parabolic trajectory. That’s much as would happen if you were to throw a ball into the air to reach its target.
The pull-up or boost-glide method extends the range by starting with a normal parabolic arc. That sends the missile above the atmosphere on the initial thrust, which then re-enter the atmosphere in the normal way.
The boost-glide comes in when the missile pulls up by altering its wing angle. That aims it back up above the atmosphere. Above the atmosphere there is less drag, so the missile is catapulted forward faster and further on a second arc.
According to Wikipedia, the method dates from 1941 when German engineers hoped to attack America with long-range missiles.
The thing is that time spent in the atmosphere heats up missiles because of the friction drag. The hope therefore was to allow missiles to cool off above the atmosphere between time spent in the atmosphere.
The German idea didn’t come to anything. That was because missiles of the period heated up too much between skips and wouldn’t survive the trip. The Germans revived the idea later in the war, but it never came to anything. After the war, both Russia and the US pursued the idea. That came to a halt with the development of powerful Intercontinental missiles made the pull-up method redundant.
That was until the military realised there was a second use of the pull-up method. In the latest versions of pull-up, a missile might perform a number of skips. That makes it able to travel faster and less predictably, thereby overcoming air defences.
And now full circle to North Korea, which doest not have enough capability to build an intercontinental ballistic missile. It can, however, can use the skip method to extend the range of smaller missiles.