Reentry Heating from North Korea’s July 4 Missile Test

July 7, 2017
David Wright
Former contributor

In a previous post, I estimated what North Korea could have learned from its May 14 Hwasong-12 missile test that is relevant to developing a reentry vehicle (RV) for a longer range missile.

I’ve updated the numbers in that post for the July 4 missile test (Table 1). In particular, I compare several measures of the heating experienced by the RV on the July 4 test to what would be experienced by the same RV on a 10,000 km-range missile on a standard trajectory (MET).

Table 1. A comparison of RV heating on the July 4 test and on a 10,000 km-range trajectory, assuming both missiles have the same RV and payload. A discussion of these quantities can be found in the earlier post.

The numbers in Table 1 are very nearly the same as those for the May 14 test, which means this test would give only a marginal amount of new information.

The maximum heating rate (q) would be essentially the same for the two trajectories. However, the total heat absorbed (Q) by the 10,000 km missile would be 60% larger and the duration of heating (τ) would be more than two and a half times as long.

In its statement after the July 4 test, North Korea said:

the inner temperature of the warhead tip was maintained at 25 to 45 degrees centigrade despite the harsh atmospheric reentry conditions of having to face the heat reaching thousands of degrees centigrade

While this may be true, the additional heat that would be absorbed on a 10,000 km trajectory and the longer time available for that heat to conduct to the interior of the RV means that this test did not replicate the heating environment a 10,000 km-range missile would have to withstand. The heat shield may in fact be sufficient to protect the warhead, but this test does not conclusively demonstrate that.