UCS Blog - All Things Nuclear, Missile Defense

No, Missile Defense Will Not Work 97% of the Time

In an October 11 interview on Fox News, President Trump claimed:

We have missiles that can knock out a missile in the air 97 percent of the time. If you send two of them, they are going to get knocked down.

This is not true. At least not in any relevant way.

The only homeland missile defense system is the Ground-based Midcourse Defense (GMD) system, which I’ve written plenty about here in these pages, and have co-authored a recent report about. If you’ve been following along, you’ll know the president’s statement was clearly untrue.  I’ll explain why.

What does the actual test record show?

The GMD interceptors have succeeded in destroying the target in nine out of 18 tests since 1999 (50%).  They have destroyed their target in four out of 10 tries (40%) since the GMD system was nominally deployed in 2004. They have destroyed their target in two of the last five tests (40%).

So there is no basis to expect it to work any better than 40 to 50% of the time even under the most generous and easiest conditions—former Pentagon testing agency director Phil Coyle calls the test conditions so far as “scripted for success.”

While the test record says something about the GMD’s capabilities under scripted conditions, the real world will be more complex and challenging. The Pentagon’s highest testing official assessed in 2014 that the test program was “insufficient to demonstrate that an operationally useful capability exists.” More on this later.

But for sake of argument, say the “single shot kill probability” has been determined via tests to be 40 to 50% in those optimistic conditions. Because reliability is low, the US would fire multiple interceptors at the missile to try to boost the system’s effectiveness. Using four-on-one targeting, and a 40 to 50% chance that a given interceptor would work, this leads to a 6 to 13% chance that the warhead gets through.

Real-world conditions

But this isn’t the right question. If it came down to a nuclear attack, would North Korea send just a single missile, and choose the most convenient conditions? That seems unlikely. Let’s say the salvo is five incoming missiles. In that case, with an interceptor kill probability of 40 to 50%, using four interceptors on each missile, the probability that one warhead gets through is 28 to 50%. Uncomfortably high.

I could not stress more that this is a best-case scenario. It assumes that:

1) Failures are uncorrelated and not, e.g., a design flaw common to all interceptors, such as the guidance system issues that took nearly a decade to diagnose and fix,

2) The intercept attempts take place under simplified conditions and that the system is not being stressed as it would in a real-world situation, and

3) The system successfully identified the five real targets from among decoys. If the system cannot distinguish decoys from the real targets, it will have to engage them all, quickly depleting the interceptor inventory. These do not need to be the Ferraris of decoys to be an issue. Some of the GMD intercept tests have included decoys, but all of those have been designed to be easily distinguished from the target warhead.

In short, one can construct situations under which missile defense might destroy missiles: a small salvo of missiles sent without countermeasures and under the limited range of conditions under which the system has been tested. The problem is that these are not by any stretch the most *likely* situations. A potential adversary has every incentive to make the attack as difficult as possible to intercept if he is going to initiate World War Three.

Note that even if the president were instead talking about one of the missile defense systems that has a better and more complete test record, such as THAAD, the issues with not having been tested in operationally realistic conditions is the same. And because THAAD defends against shorter-range missiles from North Korea, which are cheaper and more plentiful, it has the additional issue that it may be overwhelmed even if it is able to discriminate between decoys and real targets. There just may be too many targets.

Why is this dangerous?

The best-case scenario is that President Trump is trying to avoid a confrontation by allowing himself to save face: he has declared that North Korea must not be able to threaten the US mainland with nuclear-armed missiles. Or that he hopes such statements would help dissuade North Korea from considering an attack.

Certainly worse than this is the possibility that Trump actually believes that strategic missile defense provides credible protection and he has not been advised correctly. One hopes he is provided accurate information by stewards of these programs, although at least in public, government official often describe the GMD system as much more capable than it has been demonstrated to be.

This is dangerous, because common sense would say that if we have spent $40 billion on a missile defense system that the US has claimed has been “operational” for going on fifteen years, it must “work.” But it doesn’t. Look at the test record.

The problem is that believing missile defense works when it doesn’t can lead you to take actions that make you need it, and then it can’t help you.

North Korea’s Sept. 15 Missile Launch over Japan

North Korea conducted another missile test at 6:30 am September 15 Korean time (early evening on September 14 in the US). Like the August 28 test, this test appears to have been a Hwasong-12 missile launched from a site near the Pyongyang airport. The missile followed a standard trajectory—rather than the highly lofted trajectories North Korea used earlier this year—and it flew over part of the northern Japanese island of Hokkaido (Fig. 1).

Fig. 1. Approximate path of the launch.

The missile reportedly flew 3,700 kilometers (km) (2,300 miles) and reached a maximum altitude of 770 km (480 miles). It was at an altitude of 650 to 700 km (400 to 430 miles) when it passed over Hokkaido (Fig. 2).

Fig. 2. The parts of Hokkaido the missile flew over lie about 1,250 to 1,500 km (780-930 miles) from the missile launch point.

The range of this test was significant since North Korea demonstrated that it could reach Guam with this missile, although the payload the missile was carrying is not known. Guam lies 3,400 km from North Korea, and Pyongyang has talked about it as a target because of the presence of US forces at Anderson Air Force Base.

This missile very likely has low enough accuracy that it could be difficult for North Korea to use it to destroy this base, even if the missile was carrying a high-yield warhead. Two significant sources of inaccuracy of an early generation missile like the Hwasong-12 are guidance and control errors early in flight during boost phase, and reentry errors due to the warhead passing through the atmosphere late in flight. I estimate the inaccuracy of the Hwasong-12 flown to this range to be likely 5 to 10 km, although possibly larger.

Even assuming the missile carried a 150 kiloton warhead, which may be the yield of North Korea’s recent nuclear test, a missile of this inaccuracy would still have well under a 10% chance of destroying the air base. (For experts: This estimate assumes the air base would have to fall within the warhead’s 5 psi air blast radius, which is 3.7 km, and that the CEP is 5 to 10 km.)

Heating of the reentry vehicle

As I’ve done with some previous tests, I looked at how the heating experienced by the reentry vehicle (RV) on this test compares to what would be experienced by the same RV on a 10,000 km-range missile on a standard trajectory (MET). My previous calculations were done on North Korea’s highly lofted trajectories, which tended to give high heating rates but relatively short heating times.

Table 1 shows that in this case the duration of heating (τ) would be roughly the same in the two cases. However, not surprisingly because of the difference in ranges and therefore of reentry speeds, the maximum heating rate (q) and the total heat absorbed (Q) by the RV on this trajectory is only about half that of the 10,000 km trajectory.

Table 1. A comparison of RV heating on the September 15 missile 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.

So while it seems likely that North Korea can develop a heat shield that would be sufficient for a 10,000 km range missile, this test does not demonstrate that.

North Korea’s Missile Test over Japan

Yesterday’s missile launch by North Korea is reported to have been launched from a site near the capitol city of Pyongyang (Sunan) and landed 2,700 kilometers (km) (1,700 miles) to the east after flying over part of the Japanese island of Hokkaido. The missile reportedly flew to a maximum altitude of about 550 km (340 miles), reaching Hokkaido after about eight minutes of flight and splashing down after 14 to 15 minutes.

Fig. 1 shows a possible trajectory for the flight, although it is possible the missile flew somewhat further north and passed over more of Hokkaido.

Fig. 1 (Source: Google Earth)

The launch appears to have been of a Hwasong-12 missile, since it is the only known missile able to reach this distance. The range of this test, however, was much shorter than that of the May 14 test of the Hwasong-12, which would have had a range on a standard trajectory of about 4,800 km (3,000 miles).

What accounts for the shorter range?

One possibility is that the missile was flown with a much larger payload on this flight than on the May 14 test. However, even assuming the May 14 test only carried a payload of 150 kg (corresponding to an empty RV), this launch would have required a payload of about 1,300 kg to give the reported trajectory. That seems unlikely.

A second possibility is that it was flown on a depressed trajectory to reduce the range from 4,800 to 2,700 km. However, that would require a severely depressed trajectory with a burnout angle below nine degrees and a maximum altitude of only 150 km (95 miles). That would also give flight times that were much shorter than those reported.

A more likely reason for a shorter range is a shorter burn time for the engines, either due to North Korea terminating the thrust early to reduce the range, or possibly due to a mechanical problem. In particular, I find if the burn time of the engine is reduced by about eight seconds from the time of about 151 second for the May 14 launch, the missile will fly on the reported trajectory (Fig. 2).

If flown on a standard trajectory (a “minimum-energy trajectory”), a missile with this range would reach a maximum altitude of about 630 km (390 miles) with a burnout angle of 38.1 degrees. The reported altitude of 550 km on yesterday’s launch would mean it was slightly depressed from normal, with a burnout angle of 33.6 degrees. This amount of depression does not seem particularly significant, and may not have been intended.

Fig. 2. The apparent trajectory of yesterday’s launch. Cape Erimo on Hokkaido is at a range of about 1525 km.

A missile on this trajectory would reach the closest part of Hokkaido after eight minutes, which seems to agree with reports. It would pass over Cape Erimo after 9 minutes, and would splash down at 15.5 minutes

Flying over Japan

Yesterday’s launch was the first time North Korea flew a ballistic missile over Japanese territory, although in 1998 and 2009 it launched rockets that overflew Japan on failed attempts to put satellites into orbit. It has gone to some lengths to avoid flying over Japan, by launching its missile tests on highly lofted trajectories so they will land in the Sea of Japan. In addition, it has directed its more recent satellite launches to the south, even though it is preferable to launch to the east—over Japan—since it allows the rocket to gain speed from the rotation of the earth.

After its threats of firing Hwasong-12 missiles near Guam, it is interesting that North Korea fired this missile to the east rather than in the direction of Guam, which might have been interpreted as an attack despite the short range. The missile also appears to have flown in a direction that did not pass over highly populated parts of Japan.

It is not clear what new North Korea would have learned from this launch that is relevant to a long-range missile. It would not have been useful in simulating the reentry forces and heating of a long range missile; in particular, the heating would have been only about half of that on a 10,000 km range missile.

The launch could be useful in getting information about reentry on a standard, non-lofted trajectory with a missile that could reach Guam, although that would require a missile with about 3,400 km range rather than the 2,700 km of this flight.

North Korean ICBM Appears Able to Reach Major US Cities

Based on current information, today’s missile test by North Korea could easily reach the US West Coast, and a number of major US cities.

Reports say that North Korea again launched its missile on a very highly lofted trajectory, which allowed the missile to fall in the Sea of Japan rather than overflying Japan. It appears the ground range of the test was around 1,000 km (600 miles), which put it in or close to Japanese territorial waters. Reports also say the maximum altitude of the launch was 3,700 km (2,300 miles) with a flight time of about 47 minutes.

If those numbers are correct, the missile flown on a standard trajectory the missile would have a range 10,400 km (6,500 miles), not taking into account the Earth’s rotation.

However, the rotation of the Earth increases the range of missiles fired eastward, depending on their direction. Calculating the range of the missile in the direction of some major US cities gives the approximate results in Table 1.

Table 1.

Table 1 shows that Los Angeles, Denver, and Chicago appear to be well within range of this missile, and that Boston and New York may be just within range. Washington, D.C. may be just out of range.

It is important to keep in mind that we do not know the mass of the payload the missile carried on this test. If it was lighter than the actual warhead the missile would carry, the ranges would be shorter than those estimated above.


Reentry Heating from North Korea’s July 4 Missile Test

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.

North Korea Appears to Launch Missile with 6,700 km Range

Current reports of North Korea’s July 4 missile test say the missile had a range of “more that 930 km” (580 miles), and flew for 37 minutes (according to US Pacific Command).

A missile of that range would need to fly on a very highly lofted trajectory to have such a long flight time.

Assuming a range of 950 km, then a flight time of 37 minutes would require it to reach a maximum altitude of more than 2,800 km (1700 miles).

So if the reports are correct, that same missile could reach a maximum range of roughly 6,700 km (4,160 miles) on a standard trajectory.

That range would not be enough to reach the lower 48 states or the large islands of Hawaii, but would allow it to reach all of Alaska.

There is not enough information yet to determine whether this launch could be done with a modified version of the Hwasong-12 missile that was launched on May 14.