UCS Blog - All Things Nuclear, Missile Defense

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.

Tillerson, Mattis and the Chinese

Rex Tillerson and James Mattis are talking to their Chinese counterparts. The conversation is just getting started but it appears to be constructive. Their remarks to the press after a recent meeting in Washington with State Councilor Yang Jiechi and General Fang Fenghui should calm Asian fears about potentially destabilizing changes to US policy in the region.

US Secretary of State Rex Tillerson and US Secretary of State James Mattis meet with Chinese State Councillor Yang Jiechi and General Fang Fenghui, Chief of the General Staff of China’s People’s Liberation Army in Washington on 21 June 2017.

No Panic on North Korea

Mattis addressed concerns about North Korea’s nuclear program by reminding reporters that, “China’s end state on the Korean Peninsula in terms of nuclear weapons is the same as ours, and we continue to work towards that end state.”  Tillerson added that the United States and China “affirmed our strong commitment to cooperate, including through the UN, to realize our shared goal of denuclearization of the Korean Peninsula.”

China’s People’s Daily emphasized the need for “continued peace and stability” on the Korean penninsula and “resolving problems through negotiations.” It highlighted a proposal to reconstitute diplomatic talks around a “joint freeze” that would require the United States and its regional allies to stop regular military exercises in return for a halt in North Korean nuclear and missile tests.

Tillerson responded cooly to the “joint freeze” proposal, noting that the United States “will continue to take necessary measures to defend ourselves and our allies.”

Preserving Strategic Stability

The former Exxon executive reiterated his desire to focus on the long-term. He wants to use the new dialogues with China to redefine “how we’re going to engage and how we’re going to live with one another over the next 40 years.” Tillerson announced that “US and Chinese civilian and military teams” will “start discussions in new areas of strategic concern like space, cyberspace, nuclear forces, and nonproliferation issues.”

If those discussions do indeed take place it would represent a significant step forward in US and Chinese efforts to manage technologies both sides see as potent sources of military advantage that could undermine strategic stability.

The People’s Daily, which is owned and operated by the Chinese Communist Party, focused its description of the talks on the issues that could lead to a military conflict rather than the weapons that might be used after it starts. It reported that “the American side indicated the US government adheres to pursuing the one-China policy, that the United States recognizes Tibet is a part of China and that it does not support activities to divide or break up China.”

Neither Tillerson nor Mattis specifically mentioned Taiwan or Tibet, although Tillerson did resurrect  traditional US talking points on China’s on human rights record.

Thucydides Trappings

Politico reported that the Secretary of Defense, the National Security Adviser and other senior members of the Trump administration are turning to the ancient Greeks for guidance on US-China policy. Hopefully, the impetus is a desire to avoid war, but history buffs with a fixation on the rise and fall of nations can have other motivations. Mattis told the press that “while competition between our nations is bound to occur, conflict is not inevitable.” Steve Bannon, on the other hand, may believe that if the United States and China are destined for war, as Harvard’s Graham Allison suggests, history may hold the key to US victory.

Ancient wisdom is not always the best answer to contemporary problems. The marriage counselor who sends his patients to Plato’s Phaedrus to discover the true meaning of human love is less apt to be successful than the one who helps troubled couples talk through the arguments that drove them apart. Tillerson and Mattis may find it more helpful to review the unsettled history of the US government’s relationship with the Chinese Communist Party than to look for the true cause of human conflict in The History of the Peloponnesian War.

Productive leaders tend to be more interested in the promise of the future than the problems of the past.  A dialogue that begins with a frank airing of old grievances can be cathartic. Skilled negotiators can use it to help build trust, encourage compromise and facilitate cooperation. Tillerson’s focus on the next forty years of the US-China relationship is encouraging and unsurprisingly businesslike.

For now, at least, Asia can rest a little easier knowing the governments of the United States and China are willing and able to talk constructively.

Upcoming GMD Missile Defense Test: Part 2

The upcoming missile defense test will also be the first intercept test of a new kill vehicle and will use an upgraded booster for the interceptor.

The GMD system currently has 36 deployed interceptors. A majority of the interceptors use a type of kill vehicle, the CE-I variant, that has had only two successful intercept tests in four tries. Its last successful intercept test was in 2008; the most recent test failed.

The other interceptors are equipped with the CE-II kill vehicle, which has had only a single successful intercept test in three tries. The Director of Operational Test and Evaluation’s 2014 report stated: “The reliability of the interceptors is low, and the [Missile Defense Agency (MDA)] continues discovering new failure modes during testing.”

The upcoming test will be the first intercept test of the new CE-II Block 1 kill vehicle. It uses newly designed divert thrusters meant to fix persistent problems guiding the kill vehicle. The divert thrusters are the small motors that make course adjustments when the kill vehicle is homing on its target. They make the fine adjustments in direction that make the difference between a hit and a miss.

The kill vehicle is the heart of the homeland missile defense system. Yet it has been dogged by a persistent problem called the track gate anomaly, which has appeared in tests for more than a decade, and which led to a failed intercept in 2010. The MDA has tried software and hardware fixes, essentially to compensate for vibrations caused by the rough combustion of the small divert motors. The CE-II Block 1 kill vehicle uses a new set of those motors to try to solve this problem. It was flight tested in January 2016, without complete success. In that case, one of the four motors stopped working and the kill vehicle flew off course—way off course.

The improved interceptor booster has upgraded avionics, and addresses obsolescence and reliability issues.

What if the test fails?

The MDA has been committed to increasing the number of interceptors to 44 before the end of 2017. To do so, it will be emplacing 10 new interceptors with CE-II Block 1 kill vehicles on them (eight CE-II Block 1 interceptors to complete the fleet and two to replace older interceptors equipped with the CE-I kill vehicle.) The MDA Director stated in testimony that he is waiting for the (presumably) successful intercept test before delivering these.

While that may seem an obvious criterion, that’s not the way GMD business has been done in the past. All (or nearly all) other currently-fielded GBI were fielded before they had completed a successful intercept test, as is shown in Fig. 1.

Fig. 1. This shows the number of deployed interceptors with the CE-I and CE-II kill vehicles (vertical axis) and the tests of those kill vehicles. (Source: “Shielded from Oversight”)

So, should this test fail, a consequence may be that the interceptor fielding would be put on hold until the test was repeated successfully. Because GMD tests take a significant amount of time to plan and organize, this is unlikely to happen quickly. For example, the January FTG-06 2010 intercept test failed and was repeated in December of that year.

Will political pressure to field these interceptors win out even if the test fails?

What if it’s a success?

Even if the test is successful, it is very important to look wholistically at the capabilities of the system and what has actually been demonstrated. While this test may demonstrate that the MDA is on the right track with the fixes to the kill vehicle, overall it is not even close to demonstrating that the system works in a real-world setting. The system has not yet been tested in the range of conditions under which it is expected to operate—for example, it hasn’t been successfully tested at night or against complex countermeasures that a determined adversary would surely try to include. The Pentagon’s Director for Operational Test and Evaluation assessment in 2014 is that the tests to date are “insufficient to demonstrate that an operationally useful defense capability exists.”

A successful test this week is the basis for better understanding the capabilities of the system, but it is not the basis for expanding the system.

Upcoming GMD Missile Defense Test: Part 1

Scheduled for later this week is the 18th intercept test of the Ground-based Midcourse Defense (GMD) system since 1999, and the 10th since the system was declared operational in 2004. What do we know about the test, and what’s riding on it?

The GMD system is, after more than 15 years on an accelerated deployment schedule and on order of $40 billion spent, still essentially an advanced prototype. It has serious reliability issues. In 9 of the 17 intercept tests since 1999, the kill vehicle failed to destroy the target. The test record has not been getting better over time as you would expect for a system that is maturing. And the tests have still not been done under realistic conditions.

The Missile Defense Agency (MDA) has said the upcoming test will be the first test against an ICBM-range target missile. Defending against long-range missile is, of course, what the whole system is about.

MDA classifies targets for the GMD system as intermediate range ballistic missiles (IRBM) (3,000-4,500 km) and intercontinental ballistic missiles (ICBM) (>5,500 km). This test will apparently use a three-stage ICBM-range target.

That leads to an important issue: what do we know about the target and how representative is it of what the US might face?

I was able to get the hazard zones for the test from the published Notices to Mariners for May 31-June 1, which are plotted in white in Google Earth. Figure 1 shows the zones where the stages will land from the launch of the target missile from Kwajalein and the interceptor from Vandenberg. These zones indicate the direction those missiles were launched. The large white region in the center is where debris from the intercept would land.

These zones allow us to determine that the target and interceptor will meet essentially head-on, and allow us to estimate the range of the target missile.

Fig. 1

A straight flight out of Kwajalein (thin white line in Fig. 2) would send the target north of the intercept zone, so the target missile apparently maneuvers during boost phase to follow the light blue line and make the collision with the GMD interceptor (yellow line) more head-on.

Fig. 2

The hard limit of the range of the target is about 5,800 km. If its range were any longer, it would land east of the hazard zone. So the target appears to be just slightly longer than the minimum range (5,500 km) considered to be an ICBM.

One important factor in a missile defense intercept is the closing speed of the engagement, how fast the distance between the target and interceptor disappears. This depends on the speeds of both the target and interceptor and the angle at which they approach. The angle of attack is significant: a head-on collision maximizes closing speed and a tail chase minimizes it.

Faster closing speeds give the interceptor less time to make course corrections, and are therefore more stressing for the interceptor. Table 1 shows the burnout speeds of missiles of various ranges on standard trajectories.

Table 1.

The conclusion I make from this is that the upcoming missile defense test is likely to be against an ICBM-range target that is marginally longer range than an IRBM, but significantly shorter range than missiles North Korea would need to target the United States. However, the closing velocity is likely to be larger than in many of the previous tests, which have been at significant crossing angles or with slower targets.

In Part 2 of this post, I look at what else is new in this test, and what the implications are.

North Korea’s May 21 Missile Launch

A week after the test launch of an intermediate range Hwasong-12 missile, North Korea has tested a medium-range missile. From press reports, this appears to be a Pukguksong-2 missile, which is the land-based version of the submarine launched missile it is developing. This appears to be the second successful test of this version of the missile.

South Korean sources reported this test had a range of 500 km (300 miles) and reached altitude of 560 km (350 miles). If accurate, this trajectory is essentially the same as the previous test of the Pukguksong-2 in February (Fig. 1). Flown on a standard trajectory, this missile carrying the same payload would have a range of about 1,250 km (780 miles). If this test was conducted with a very light payload, as North Korea is believed to have done in past tests, the actual range with a warhead could be significantly shorter.

Fig. 1: The red curveis reportedly the trajectory followed on this test. The black curve (MET=minimum-energy trajectory) is the same missile on a maximum range trajectory.

The Pukgukgsong-2 uses solid fuel rather than liquid fuel like most of North Korea’s missiles. For military purposes, solid-fueled missiles have the advantage that they have the fuel loaded in them and can be launched quickly after moving them to the launch site. With large liquid-fuel  missiles you instead need to move them without fuel and then fuel them once they are in place at the launch site. That process can take an hour or so, and the truck carrying the missile must be accompanied by a number of trucks containing the fuel. So it is easier to spot a liquid missile before launch and there is more time available to attack it.

However, it is easier to build liquid missiles, so that is typically where countries begin. North Korea obtained liquid fuel technology from the Soviet Union in the 1980s, and built its program up from there. It is still in early stages of developing solid missiles.

Building large solid missiles is difficult. If you look at examples of other countries building long-range solid missiles, e.g., France and China, it took them several decades to get from the point of building a medium-range solid missile, like North Korea has, to building a solid ICBM. So this is not something that will happen soon, but with time North Korea will be able to do it.

Warhead Reentry: What Could North Korea Learn from its Recent Missile Test?

As North Korea continues its missile development, a key question is what it may have learned from its recent missile test that is relevant to building a reentry vehicle (RV) for a long-range missile.

The RV is a crucial part of a ballistic missile. A long-range missile accelerates its warhead to very high speed—16,000 mph—and sends it arcing through space high above the atmosphere. To reach the ground it must reenter the atmosphere. Atmospheric drag slows the RV and most of the kinetic energy it loses goes into heating the air around the RV, which then leads to intense heating of the surface of the RV. The RV absorbs some of the heat, which is conducted inside to where the warhead is sitting.

So the RV needs to be built to (1) withstand the intense heating at its outer surface, and (2) insulate the warhead from the absorbed heat that is conducted through the interior of the RV.

The first of these depends on the maximum heating rate at the surface and the length of time that significant heating takes place. Number (2) depends on the total amount of heat absorbed by the RV and the amount of time the heat has to travel from the surface of the RV to the warhead, which is roughly the time between when intense heating begins and when the warhead detonates.

I calculated these quantities for the two cases of interest here: the highly lofted trajectory that the recent North Korean missile followed and a 10,000 km missile on a normal (MET) trajectory. The table shows the results.

The maximum heating rate (q) is only about 10% higher for the 10,000 km range missile than the lofted missile. However, the total heat absorbed (Q) is nearly twice as large for the long-range missile and the duration of heating (τ) is more than two and a half times as long.

This shows that North Korea could get significant data from the recent test—assuming the RV was carrying appropriate sensors and sent that information back during flight, and/or that North Korea was able to recover the RV from the sea. But it also shows that this test does not give all the data you would like to have to understand how effective the heatshield might be before putting a nuclear warhead inside the RV and launching it on a long-range missile.

Some details

The rate of heat transfer per area (q) is roughly proportional to ρV3, where ρ is the atmospheric density and V is the velocity of the RV. Since longer range missiles reenter at higher speeds, the heating rate increases rapidly with missile range. The total heat absorbed (Q) is the integral of q over time during reentry.

This calculation assumes the ballistic coefficient (β) of the RV is 48 kN/m2 (1,000 lb/ft2). The heating values in the table roughly scale with β. A large value of β means less atmospheric drag so  the RV travels through the atmosphere at higher speed. That increases the accuracy of the missile but also increases the heating. The United States worked for many years to develop RVs with special coatings that allowed them to have high β and therefore high accuracy, but  could also withstand the heating under these conditions.

The results in the table can be understood by looking at how RVs on these two trajectories slow down as they reenter. Figs. 1 and 2 plot the speed of the RV versus time; the x and y axes of the two figures have the same scale. The maximum deceleration (slope of the curve) is roughly the same in the two cases, leading to roughly the same value of q. But the 10,000 km range missile loses more total energy—leading to a larger value of Q—and does so over a longer time than the lofted trajectory.

North Korea’s Missile in New Test Would Have 4,500 km Range

North Korea launched a missile in a test early in the morning of May 14, North Korean time. If the information that has been reported about the test are correct, the missile has considerably longer range than its current missiles.

Reports from Japan say that the missile fell into the Sea of Japan after traveling about 700 km (430 miles), after flying for about 30 minutes.

A missile with a range of 1,000 km (620 miles), such as the extended-range Scud, or Scud-ER, would only have a flight time of about 12 minutes if flown on a slightly lofted trajectory that traveled 700 km.

A 30-minute flight time would instead require a missile that was highly lofted, reaching an apogee of about 2,000 km (1,240 miles) while splashing down at a range of 700 km. If that same missile was flown on a standard trajectory, it would have a maximum range of about 4,500 km (2,800 km).

New press reports are in fact giving a 2,000 km apogee for the test.

Fig. 1  The black curve is the lofted trajectory flown on the test. The red curve is the same missile flown on a normal (MET) trajectory.

This range is considerably longer than the estimated range of the Musudan missile, which showed a range of about 3,000 km in a test last year. Guam is 3,400 km from North Korea. Reaching the US West Coast would require a missile with a range of more than 8,000 km. Hawaii is roughly 7,000 km from North Korea.

This missile may have been the new mobile missile seen in North Korea’s April 15 parade (Fig. 2). It appears to be a two-stage liquid-fueled missile.

Fig. 2 (Source: KCNA)