youzicha

collapsedsquid:

I believe it’s partly because it’s an installation for detailed monitoring of Chinese airspace, and partly it’s the classic argument against nuclear defense which is basically “Why do you want this so much unless you are intending a first strike?“.

In the time between sending the ask and getting the answer, I also did some more reading about THAAD myself. I found two documents particularly helpful, a report from the U.S. Congressional Research Service Ballistic Missile Defense in the Asia-Pacific Region: Cooperation and Opposition, and a blogpost This Is Why China Fears THAAD.

One thing that I have been trying to figure out myself is how much of an issue the radar coverage into China is; different authors disagree a lot on this. I’m not sure that I managed to do so, but it was a fun excuse to play around in Google Earth.

First note that although the long range of the radar (estimates vary from 480 km to 3,000 km) lets it reach very far into Chinese territory, it’s limited by looking over the horizon. The distance from the Seongju golf course to the closest point on the coast of china (near Weihai, in Shandong province) is about 515 km. That corresponds to a horizon drop of 20,800 m (or 68,200 feet), which is about how high a Lookheed U-2 can fly. I don’t think the Chinese airforce has any planes that can reach this altitude (e.g. the service ceiling of an Su-35 is 18,000m). Most of China is of course still more remote, e.g. Shanghai is 800km away (a 50,000m drop) and Tianjin is 990 km away (a 75,000m drop). So although the radar can see a large volume of Chinese airspace, it will not be able to see any airbreathing objects. The only thing it can observe is ballistic missiles.

When it comes to ballistic missile targets, the AN/TPY-2 radar can be used in two modes. In Terminal Mode it tracks incoming targets as it guides THAAD interceptors to them. This is how the Korean radar will be set up. The range in this mode is said to be 600km, which is just enough to cover North Korea while not seeing much of China. However, such range estimates entirely depend on what kind of objects the radar tracks. In terminal mode the targets are head-on incoming warheads (so the radar cross section is small), there will be several targets (so there is less time to dwell on each one), and it’s not known where they will be (so the radar will need to spend time searching the entire sky).

In Forward-Based mode, the radar is used to provide early tracking of missile launches. Satellites will detect the launch of an ICBM and send the approximate position to the forward-based radar. The radar will measure the track of the missile and pass that on to other radars, which then have a greater effective range because they will know where to look. There are already two forward-based radar sites in Japan (in Aomori and in Kyoto prefectures), which are part of a Bush-era anti-ballistic missile system intended to defend the continental United States from a small-scale North Korean ICBM attack (a single missile with no countermeasures). Because the target is a large missile, and the radar is cued, the range will be larger. Exactly hard long is hard to say—by tweaking the assumptions you can make it big or small, and the actual numbers are secret—but say maybe 2000km.

At a few hours’ notice, the Korean radar could also be put into forward-based mode, and maybe even turned west, in which case it could see far into China (at the cost of no longer protecting against North Korean missile attacks). China would easily be able to detect if this happened, but they couldn’t do anything about it except complain.

China has stated that the new Korean radar threatens their ICBM deterrence, but officially they have not specified any specific concerns. I think the use of it as a forward-based cueing radar could be one such use. The most specific information about possible U.S. missile defense systems that I found is the 2012 report Making Sense of Ballistic Missile Defense, which was written with access to classified information. They specifically mention THAAD batteries in this role, and contrast this with the expensive (and subsequently cancelled) PTSS satellite surveillance system: “While PTSS is a hedge against the inability to negotiate a forward site for this AN/TPY-2 radar, the value added by PTSS is very low and comes at a very high cost”.

Different people disagree about how effective the Korean radar would be in this role. Assuming a 2000km range, the radar in Aomori could already track missiles fired from central China towards the U.S. west coast, but not missiles towards the east coast. The Korean radar might be close enough to see missiles towards the east coast also. Of course, even the east coast trajectory is within line-of-sight of Japan, and if the U.S. tried to build a system to defend against Chinese ICBMs, upgrading the Japanese radar would not be the biggest cost.

There is one more potential use of the radar against ICBMs, which is also mentioned in Making Sense. In order to create a missile defense system which has some capability against missiles with countermeasures, they propose what they call a GBX radar, which would consist of two AN/TPY-2 antennas (to double the resolution) mounted on a mechanical turntable. These radars would observe incoming missiles at mid-course and try to discriminate re-entry vehicles from decoys. Various authors have suggested the Korean radar could be used similarly, to observe missiles as they are deploying MIRVs and countermeasures. I think this is a bit of a red herring; the range at which this could be done would be much shorter (since the warheads are smaller than the full missile, and because you need much better signal/noise ratio to measure the shape of an object than to just track its location). If you want an anti-ICBM role for these radars, the early tracking one seems more plausible.

These concerns are about the future: nobody thinks that the current U.S. missile defense could intercept Chinese ICBMs. (Indeed, as we saw in the April 2017 North Korean nuclear mess, nobody even trusts it would intercept a North Korean one.) But if the U.S. did decide to build up their missile defenses along the lines described in the NAS report above, the system would probably include early warning / early tracking radars in Japan or Korea or Taiwan. This particular radar might not make much difference on its own, but maybe it’s the principle of the thing.

(One thing that I had not appreciated before is that unlike Russia, China’s nuclear force is actually very small—maybe around 25 ICBMs that can reach the contiguous U.S. So it’s hard to build an ICBM defense system which could reliably protect the U.S. against North Korea without affecting China’s nuclear deterrent. Both Russia and China are now restructuring their forces as a response to American missile defenses; in China’s case by beginning to MIRV, by making their missiles road mobile (to better resist an American first strike), and by (maybe) developing manueverable re-entry vehicles. Eventually China may also build more missiles.)

A separate concern is that if the radar was if redirected westward could be used to gather intelligence/spy on Chinese peacetime missile tests. Such tests often involve launch complexes in the interior of China (Jiuquan, Xichang, Korla). These are so far away from Korea (2500km, 2600km, 3600km) that the new radar would probably not be very helpful. However, ICBM test flights are launched westwards from Taiyuan, which is only 1500km away from Seongju, so the Korean radar would be able to look at their tail end as they leave.

It’s unclear how much additional useful intelligence the new radar could give. Since 2013, there is already a PAVE PAWS radar in Taiwan which has a longer range than the AN/TPY-2 and is also even better placed to see into China. But having views of the the same missile from behind might be helpful, the PAVE PAWS is old, and it operates in the UHF-band while for anti-missile development it would be useful to have data in the X-band. However, I don’t think that land-based radars are absolutely necessary for missile intelligence. Historially, characterizing enemy re-entry vehicles for missile defense purposes was done using ship-based radars, which can be both more powerful than the AN/TPY-2 and more flexibly positioned.

To sum up, the radar seems to make a very incremental difference. If deployed in its intended tracking mode it will not see much. If repurposed as a forward-based anti-ballistic missile radar it could be one component in a hypothetical future U.S. missile defense system, but might not add very much given the existing radars in Japan. It could give some additional intelligence, but not much more than the radar in Leshan, Taiwan. Admittedly China complained about Kyoto and Leshan also, so maybe the reason they are making a bigger deal this time is just because the have more leverage over Korea.

Probably some of China’s concerns are purely political—they do not want any military cooperation between Korea and Japan. But as for the capabilities offered by THAAD system itself, I get the feeling that an elephant in the room is conventional ballistic missile defense. As the Congressional Research Service report puts it,

The potential for BMD programs to undermine the effectiveness of other Chinese uses of conventional ballistic missiles. China has not made this argument prominently, possibly out of an unwillingness to highlight potential offensive uses of its ballistic missiles outside of a Taiwan context, and perhaps because it tacitly recognizes a U.S. right to develop tactical BMD systems that do not undermine strategic stability. Wu Riqiang notes that China’s conventional Ballistic Missile Defense in the Asia-Pacific Region: Cooperation and Opposition Congressional Research Service ballistic missile capability “gives the United States a reasonable motivation to develop tactical BMD systems. But certain tactical BMD assets can be used for strategic purposes, thereby undermining Sino-American strategic stability.” A 2013 CSIS report asserts that U.S. BMD programs are not intended to compromise China’s long-range nuclear deterrent, but “China’s significant shorter-range missile capability, especially those missiles that threaten U.S. military forces in the region as well as U.S. allies and partners, are, however, a legitimate and necessary target for U.S. theater missile defense.”

That is, it is convenient to emphasise defense against nuclear-armed ICBMs, because this is a topic where it’s internationally accepted that one must not upset the balance. But all the consequences for ICBM second-strike capabilities are marginal or speculative: if the U.S. upgraded the radar in the future, and retargeted it, then China maybe would have to make a bigger investment in countermeasures to nullify it, etc etc. The capability that it definitely does add is better defense against missile strikes in Korea (which is not very diplomatic to bring up!). Fan Gaoyue, retired senior colonel and former chief specialist at PLA academy of military science, writes:

THAAD in South Korea will cause chain reactions. The deployment of THAAD in South Korea might stimulate the deployment of THAAD at Aomori Prefecture, Kyoto Prefecture, and Okinawa in Japan, as well as Manila in the Philippines and potentially other places. This, combined with Patriot and Aegis missile defense systems deployed in the region would constitute an integrated missile defense system of low, medium, and high altitude defense capabilities. Such a missile defense system forms an enormous missile defense arc, which greatly impairs the strategic deterrence capabilities of China and Russia.

China surely doesn’t intend to strike the Philippines “and potentially other places” with nuclear weapons, but they definitely want to target U.S. military bases there with conventional ballistic missiles. Maybe the strategic deterrence capability that is most threatened is not nuclear, but rather the capability to use conventional strikes to deter the U.S. from interfering in East Asia.