Mauger on China’s Hypersonic Test

AS James Acton, Catherine Dill and I prepared our “Crashing Tiger, Hidden Hotspring” post, one of my students, Philippe Mauger, made a number of important observations including offering a possible identification of the rocket engine found among the debris. I asked Philippe to write up some of his observations.

Hypersonic loose ends
A short addendum to the “Crashing Tiger, Hidden Hotspring” piece.

Philippe Mauger

1.
Identifying Taiyuan as the correct launch site

A publicly announced satellite launch took place at Jiuquan at 1:45pm on August 9, less than two days after the crash. This fact should have immediately raised doubts about the initial reports that Jiuquan had been used as the launch site.

This local picture of the launch in Taiyuan, which shows the sun’s rays (top left) and a rocket plume (heading right, perpendicular to the rays), provides an additional hint that the launch was part of a military test. SunCalc can be used to fix the position of the sun in Taiyuan at the time of the test– but suffice to say that the East is, indeed, red. The rocket is thus westbound. As the main piece notes, nearly all satellite launches instead use an eastwards trajectory to take advantage of the Earth’s rotation.

2.
Liquid fueled two-stage rockets: drawing from the Soviet experience

As analyzed in the main piece, the debris markings and the fuel signature are consistent with–if not foolproof evidence of– the use of a China Aerospace (中国航天) Long March (LM) rocket. Although it is difficult to tell whether a first or second stage crashed (more on this below), it is reasonable to rule out a three-stage rocket, which would be overkill given the required performance requirements. Details about a Soviet/Russian hypersonic weapons program, published on Pavel Podvig’s blog, provide a useful reference point. It supports the two-stage-only claim, given that the Russians apparently use the two-stage, liquid-fueled SS-19 (UR-100NUTTH) as their carrier rocket.

Page 2 of the LM document referenced in the main piece provides characteristics for the entire LM rocket family. SS-19 characteristics, taken from Russia’s Arms and Technologies, Volume I: Strategic Nuclear Forces (p.69, 77-79), are reproduced below. UR-100N base characteristics are also included to fill in some gaps; these values are given in an older catalog: Russian Armament State Corporation’s Russia’s Arms Catalog, Volume VI: Missiles and Space Technology (p. 268). The two-stage Chinese LM-2C is a larger rocket than the SS-19 ICBM. Also note that the payload capacity values should not be blindly compared, given that rocket performance is highly dependent on the firing mode and mission range, which differs for both missiles. In all, even when allowing a conservative performance margin to account for a heavier and/or larger Chinese hypersonic warhead, the use of a three-stage LM rocket appears uncessary.

Characteristic	Russian UR-100N	Russian SS-19	Chinese LM-2C
Number of stages	2	2	2
Solid or liquid fuel(s)?	Both stages liquid	Both stages liquid	Both stages liquid
Height (m)	24		43.0
Diameter (m)	2.5		3.35
Launch weight (T)	103	105.6	245
Lift-off thrust (kN)			2962
Payload capacity (kg)		4350 (ballistic, 10,000km range)	3850 (space launch to LEO)

3.
The engine in the debris field, and estimating the HGV’s test range

Given the above, the crash photographs are believed to be of a first or second LM stage. Identifying which stage, however, is nontrivial. One good quality picture of the crash debris shows a badly damaged engine. In its pictured state, figuring out which part used to go where is a 10,000-piece, 3D, puzzle. But while the identification is not definitive, the rocket engine does not appear to be part of a YF-21 cluster (a cluster of four YF-20 engines) used in LM first stages. The argument in support of this claim is two-fold.

First, according to a reference manual (section 6-7: Republic of China) hosted on the FAS website, an LM first stage should have a cluster of four YF-20 engines. According to the same document, an LM second stage has a single, different, engine: a YF-22 or a YF-25. The debris, despite begin densely packed, shows the remains of only one engine. It is possible that three other engines were scattered farther out in the crash, but this is less likely than the single-engine hypothesis.

Second, each YF-20 engine in a YF-21 cluster has a “pinched” zone at the top, which does not seem to appear on the engine pictured. The website http://www.b14643.de maintains a wonderful collection of rocket engine pictures for comparison, including one of a YF-21 cluster, a YF-22, and an extended YF-22 (YF-22E). The following composite image shows the relevant portion of the broken engine in the debris field, boxed out; the “pinched” zone on a YF-20 engine taken from the linked YF-21 cluster picture; and a standard YF-22 for comparison.

If the photographs do indeed show a second stage, what follows? Given that this presumed last stage still had fuel remaining and thus did not reach its designated range, it is reasonable to conclude that the NOTAM eastern keep-out zone was its planned drop zone. The warhead would thus have been expected to separate before the NOTAM eastern keep-out zone. The Chinese HGV would then have had an expected minimum test range somewhat in excess of 1100km (the distance between both keep-out zones) and well below 1750km (the Taiyuan-Western keep-out zone distance).