HGV Unproven at IRBM Ranges: Analysis of the April 2 Hwasong-16Na Hypersonic Missile Test

On April 2, 2024, North Korea flight tested the Hwasong-16Na (referred to in English as the Hwasong-16B), a two-stage solid-propellant booster armed with a hypersonic glide vehicle (HGV), marking the second flight test of the wedge-shaped HGV developed by North Korea.

Since September 2021, North Korea has flight tested two types of HGVs, namely a conical shaped one and a wedge-shaped one.[1] In the April 2, 2024 test, the wedge-shaped HGV (atop the Hwasong-16Na) did not demonstrate any clear advantage over the conical-shaped one. In comparison, the conical-shaped HGV appears to have been tested under harsher conditions. Thus, the Hwasong-16Na system as a whole is likely still in an early phase of development.

With tests thus far at limited speed and range, it is hard to validate both HGVs at intermediate-range ballistic missile-class (IRBM) ranges. However, the HGVs have shown their potential to strike Japan if they are to be used at medium ranges. This is especially true for the conical-shaped HGV, which has been tested one more time than the HGV atop the Hwasong-16Na and has likely demonstrated a higher speed. Full-range tests are likely needed to verify the performance of both types of HGVs at true IRBM ranges. However, such tests may pose some challenges for North Korea to implement.

Overview of Pyongyang’s Hypersonic Missile Tests

From September 2021 to early April 2024, North Korea has conducted five tests of hypersonic glide vehicles (HGVs) (Figure 1). The wedge-shaped HGV was first tested in September 2021. It was tested again atop the Hwasong-16Na on April 2, 2024. The conical-shaped HGV has been tested three times from January 2022 to January 2024. Deviating from the use of liquid-propellant boosters, the HGVs tested in 2024 were positioned atop a two-stage solid-propellant booster. Detailed information regarding these tests is compiled in the table in the Annex.

As can be seen from the table, North Korean state media and the Japanese and South Korean governments have given different ranges for some of these tests. The discrepancy could be caused by: 1) exaggerated claims by North Korean state media; 2) different tactics on releasing information; and/or 3) the inability of ground-based radars in Japan and South Korea to effectively track the HGVs when the latter descended below the radars’ line of sight.[2]

Comparing the Tests

North Korean state media has published relatively rich information regarding the flight of the conical-shaped HGV tested on January 11, 2022, and the wedge-shaped HGV atop the Hwasong-16Na tested on April 2, 2024. This information, combined with data released by Japan and South Korea, offered a basis to compare the demonstrated performance of the two types of HGVs. According to North Korean announcements, the two types of HGVs have all reached a range of 1000 km during their tests.[3] However, the following two observations suggest that the conical-shaped HGV was likely tested under harsher conditions:

• North Korea reported that during the April 2, 2024 flight, the wedge-shaped HGV atop the Hwasong-16Na reached an apogee of around 100 km during its first phase glide, and a second apogee of over 70 km during its second phase glide. In comparison, ROK reports claimed the conical-shaped HGV only reached 60 km at its highest point during its flight on January 11, 2022 (Figure 2). Gliding in the denser atmosphere at lower altitudes means that the conical-shaped HGV needed higher burnout velocity (velocity when the rocket booster burns out) to overcome the greater aerodynamic drag at such altitudes.

• Both HGVs reportedly performed a “cross-range,” or turning, maneuver after their first phase glide. However, according to the flight paths North Korean media depicted as being displayed to Kim Jong Un, the turning maneuver conducted by the conical-shaped HGV appeared to be considerably steeper than the one conducted by the wedge-shaped HGV atop the Hwasong-16Na (Figure 3). This steeper turn results in the loss of more energy than the shallower turn. Thus, to reach the same intended range, higher burnout velocity was needed for the conical-shaped HGV.

These two observations suggest that the conical-shaped HGV has flown at higher velocity and withstood higher structural and temperature pressures. In addition, the steeper turn also demonstrated a higher degree of agility than the wedge-shaped HGV atop the Hwasong-16Na. In other words, despite its complex aerodynamic layout (Figure 4), the wedge-shaped HGV has not yet demonstrated in testing clear advantages over the conical shaped one. Thus, in comparison, the Hwasong-16Na system as a whole is likely still in an early phase of development.

Not Ready for IRBM Ranges Yet

Both types of HGVs have demonstrated sufficient range in flight-testing to strike targets in Japan with a highly depressed flight trajectory. As the actual distance reportedly flown by the HGVs was achieved with loss in speed and altitude caused by a turning maneuver, their maximum flight range without the turning maneuver could possibly surpass 1,000 km, putting them on par with the Hwasong-7 (Nodong) mid-range ballistic missile that mainly targets Japan. This is especially true for the conical-shaped HGV, which has been tested one more time than the HGV atop the Hwasong-16Na and has likely demonstrated a higher speed.

North Korea claimed that it had limited the speed of the Hwasong-16Na “by means of delaying the start-up of the second-stage engine and rapidly changing the flight orbit in the active region.”[4] It has also claimed both missiles tested on January 14, 2024 and on April 2, 2024 are of intermediate-range. While the two-stage solid-propellant booster used in both those 2024 tests is most likely of IRBM-class (commonly defined as 3,000 to 5,500 km range), it remains to be seen if the HGV payload could function under realistic conditions at IRBM range. For North Korea, IRBM-class missiles would need at least a 3,300 km range to reach US military bases in Guam.

North Korea’s testing standards do not necessarily follow what other states would require to certify strategic missiles as operational. However, tests without limitations on speed would offer a higher degree of confidence in the actual gliding performance, which is vital to the HGVs. Such tests may involve a mid-course flight beyond the atmosphere (during which maneuvers through reaction control mechanisms, such as via small thrusters, are possible) and, upon reentry, a long phase of glide under active control. Such a test would be more challenging to North Korea than full-range Hwasong-12 IRBM tests conducted before with traditional reentry vehicles, the terminal phase of which is brief and without active control. Without forward deployment of vessels in the Pacific, it remains unclear how North Korea would receive telemetry data from the HGVs in a full-range IRBM test, especially during the glide phase. However, novel technology solutions, such as using space-based receivers, may facilitate such tests.

Annex

1. [1]

   The conical-shaped reentry vehicle is often referred to as a maneuverable reentry vehicle instead of an HGV. It is also apparent that the wedge-shaped HGV may have better gliding characteristics than the conical-shaped reentry vehicle thanks to the former’s more advanced aerodynamic layouts. However, this article refers to both as HGVs because the conical-shaped reentry vehicle, according to announcements released by Japan, North Korea, and South Korea, has 1) reached hypersonic speed; 2) demonstrated a low altitude flight profile; and 3) conducted maneuvers during its glide phase (See Annex). These three criteria, used by aerospace company Stratolaunch, are adopted by the author as definitions for HGVs.

2. [2]

   The Japanese authority used the expression “if the missile follows a ballistic arc” as the precondition for some of the range estimates, which supports the assumption that some ground radars based in Japan could not keep track of the entire flight of the HGVs. See: Annex.

3. [3]

   According to South Korea, the conical-shaped HGV reached a 1000 km range too during the 14 January 2024 test. The January 2024 test is excluded in the comparison as North Korean media did not reveal substantial information on this test. See: Annex.

4. [4]

   A turning maneuver performed by the second stage could be observed in the KCNA video. But contrary to the KCNA claim, the second stage motor seemed to have ignited right away after first stage separation.