One of the missiles is reported to have reached a maximum altitude of 910 km (570 miles) and splashed down at a range of 450 km (280 miles) from the launch point. This missile would have had a burnout speed of about 3.74 km/s with a loft angle of 81.5 degrees, and a flight time of about 17 minutes.

If flown on a standard trajectory with the same payload, that missile would have a maximum range of about 1,900 km (1,200 miles).

This would classify the missile as medium range (1,000 to 3,500 km).

The purpose, it said, was to use “data collected and lessons learned from this test” to “inform the Department of Defense’s development of future intermediate-range capabilities.”

The real purpose of the test, however, appears to be to underscore the US decision to leave the Intermediate-range Nuclear Forces (INF) Treaty by conducting a launch that would violate the terms of the treaty. INF prohibited all US and Russian land-based missiles, or launchers for those missiles, with ranges between 500 and 5,500 km.

Was this really needed?

Reagan and Gorbachev after signing the INF Treaty in 1987 (Source: Wikipedia Commons)

Some people have argued that the United States needs to develop these weapons to fill a “gap” in its capabilities. But since the US has thousands of cruise missiles of different kinds on planes, ships, and submarines, it’s hard to make the case that launching one from the ground fills a meaningful “gap” of any kind.

For example, the US fired more than 100 Tomahawk missiles from ships at targets in Syria in 2017 and 2018. (While Tomahawks were designed to carry either nuclear or conventional explosives, they currently only carry non-nuclear warheads.)

Something isn’t right

Two things about Sunday’s test seem particularly odd:

First, the test ironically seemed to confirm concerns Russia has raised for years about a possible US violation of the INF Treaty. In particular, Russia has noted that the US missile defense system in Romania and soon to be placed in Poland uses ground-based launchers for its interceptors, and that those launchers could also be used for firing offensive missiles like the Tomahawk. This interoperability would allow the missile defense sites in Romania and Poland to be quickly converted to offensive sites.

While the United States has consistently denied this possibility, Sunday’s test indeed used the Mark-41 launch tube that is part of those missile defense systems. The Pentagon insists the system is “configured” differently to launch Tomahawks rather than interceptors, but the difference appears to be in software and not hardware. Russia would not know how long it would take to make such a change, or whether the change had already taken place.

So while US concerns about Russian violations of the INF Treaty appear to be valid, Sunday’s test appeared to verify that Russian concerns about US violations were also valid.

Second, since this system does not add any meaningful new capabilities to the US arsenal, the primary result of the test may be to increase tensions with Russia and China and potentially spur a competitive arms buildup. Doing that for no particular gain seems senseless, and potentially costly and dangerous.

The US decision to conduct this test appears to be what we sometimes call “spherically stupid”—stupid from any direction you look at it.

The Washington Post reports that Trump “has ordered his administration to prepare a push for new arms-control agreements with Russia and China after bristling at the cost of a 21st-century nuclear arms race.” If one country builds more weapons to feel secure, this can cause other countries to feel less secure and lead them to build more weapons in response. This cycle is the classic arms race.

Trump seems to get it. In December he tweeted that he wants “a meaningful halt to what has become a major and uncontrollable Arms Race.”

Fortunately, the solution is known: verifiable arms control agreements. Rather than unconstrained action/reaction cycles, agreements increase transparency between countries, limit the growth of arsenals, and set up mechanisms to clarify ambiguities and possible violations.

And it works: The United States and Soviet Union learned this lesson in the 1970s and 1980s as those reaction cycles led them to collectively build more than 60,000 nuclear weapons. A series of arms control agreements have reduced those numbers today to about 1,700 deployed weapons on each side.

Gorbachev and Reagan signing the INF Treaty in 1987  (Source: National Archives)

What Trump Needs to Do

If Trump is serious about avoiding a nuclear arms race—and a nuclear war by extension—here is what he needs to do:

• A clear first step is to extend the US-Russian New START Treaty, which is set to expire in February 2021 but can be extended for five years without new negotiations. Both countries have cut their nuclear arsenals to meet the treaty’s limits. The treaty has put in place an intrusive verification regime that the US military highly values. Extending this successful treaty will provide time to take next steps.
• The administration says it wants to go beyond New START and limit other weapons. That makes sense. But the first step is for the United States not to pull out of the Intermediate Nuclear Forces (INF) Treaty, which strictly limits weapons not covered by New START. After it was signed, the US and Soviet Union destroyed some 2,700 of these nuclear weapons. It is definitely “a bird in the hand” that is still useful as the United States and Russia work to address recent compliance issues.
• Trump must understand that the US push for defenses against long-range missiles blocks progress on limiting those weapons. When it ratified the New START treaty, Russia said any future agreement must include limits on missile defenses. And when Putin announced several new nuclear weapons last year—including the drone nuclear submarine that the United States would like to stop—it was clear that these weapons are designed to defeat missile defenses

And keep in mind that the main US missile defense system has so far cost some $45 billion, yet continues to fail half of its tests. At the same time, it can be defeated by decoys and other countermeasures. The only thing it seems certain to stop is new arms control agreements. Trump must be serious about limits on defenses if he wants to limit offenses.

• If Trump wants China to join an arms control treaty with the US and Russia he needs to be willing to think way outside the box. Both countries currently have more than 10 times as many nuclear warheads in their arsenals as does China. And China is concerned about a buildup of US missile defenses. Moreover, why would China agree to join if France and Britain, which have similarly sized arsenals, are not included? Finding incentives and a way to include China in a treaty will take some work.
• Trump must also replace National Security Advisor John Bolton. Bolton has a long history of blocking arms control: He was behind US withdrawal from the INF Treaty, and George W. Bush’s pulling out of the Anti-Ballistic Missile Treaty, among others. He has been blamed for undermining recent negotiations with North Korea.

Is Trump Serious?

Time will tell if Trump is serious. This could be a ploy to assuage the public’s growing concerns about instability and nuclear war. He may talk a good arms control game while pushing for agreements that go beyond what Russia and China are prepared to sign up to in the current climate.

But if Trump, like Reagan, understands the dangers and wastefulness of unfettered arms races, there is a lot he can do. After all, when he says “Between Russia and China and us, we’re all making hundreds of billions of dollars’ worth of weapons, including nuclear, which is ridiculous,” he’s almost right. The price tag is actually trillions of dollars.

This represents a big change. In the five years 2013 to 2017, North Korea launched more than 80 flight tests of 10 different missiles, or an average of 16 flight tests per year. In 2017 alone, it launched 20 tests of seven types of missiles, including the successful launch of two different long-range missiles.

(Source: U.S. govt.)

That testing led to big advances in its missile program.

As of 2015 the longest range missile it had successfully tested was the Nodong, with an estimated range of about 1,300 km (800 miles). In November 2017 it successfully tested an intercontinental-range missile with a range ten times that long—13,000 km (8,000 miles)—enough to reach most or all of the United States.

How Important is a Ban on Flight Testing

We know a lot about North Korea’s missile flight tests over the years because you can’t hide a missile fired through the atmosphere. The United States has satellite sensors and radars that detect and track those tests essentially anywhere in the world.

Missile flight testing is needed for several reasons:

1. To develop new missiles
2. To proof-test and determine the reliability of missiles that are being built
3. To train soldiers to use missiles in combat.

Stopping flight testing limits all three of these.

Countries typically test a new missile dozens of times before deploying it. Even though North Korea had one successful launch of its Hwasong-15 ICBM in late 2017, it has little idea whether a second test would be successful. These are very complicated mechanical systems and you need repeated testing to discover the possible failure modes and understand their probabilities.

For a missile to be militarily useful, you want to know how reliable it is. And you want to understand how likely it is to blow up on the launch pad before you decide to put a nuclear warhead on it.

In addition to this, North Korea hasn’t demonstrated a working reentry heat shield on a long-range trajectory. As long as it’s willing to accept low accuracy—which it would be if it plans to target large cities—developing a working heat shield doesn’t require advanced technology. North Korea should be able to solve this problem with time, but it is unlikely to consider these missiles militarily useful without actually demonstrating the technology on a flight test. A ban on testing keeps it from doing that.

While some press reports have said that following its one successful flight test of its Hwasong-15 ICBM, North Korea is working to mass produce it, I don’t believe they would do that. Preventing further flight tests would prevent this missile from becoming militarily useful. It would also limit operational training of military troops with its missiles.

So preserving North Korea’s ban on flight tests is an important security measure. And as noted above, a ban on flight testing has the advantage that it is completely verifiable with existing sensors.

What Does the Current Test Ban Cover?

When Kim announced the end of flight tests in April 2018, he said:

“no nuclear tests and intermediate-range and inter-continental ballistic rocket test-fire are necessary for the DPRK now. … We will discontinue nuclear tests and inter-continental ballistic rocket test-fire from April 21.”

So while North Korea has not flight tested any missiles in the past 15 months, it only announced it would stop testing long-range missiles—those with ranges longer than 5,500 km (3,500 miles). That includes the Hwasong-14 and 15 missiles.

A ban on testing long-range missiles would leave North Korea the option of continuing to develop and test intermediate and shorter range missiles. That includes the Hwasong-12, which may be able to reach US military bases in Guam. Banning only long-range flight tests would also allow North Korea to train soldiers with its existing shorter range missiles, which can reach targets in South Korea and Japan.

A key goal of the upcoming summit and future US-North Korean negotiations should be to formalize the testing ban, to make it permanent, and to extend it to cover shorter range missiles. The United States should also press for a ban on engine tests, and make clear the flight test ban includes satellite launches.

North Korea has not yet taken irreversible steps toward ending its missile program. But it has taken meaningful steps that would have been unthinkable as recently as 2017, and that suggests an openness to further steps that would be more meaningful. That would significantly advance security interests of the United States and its allies in the region.

Achieving these steps is likely to require a phased step-by-step process. There are a set of potential steps the United States could take as part of the negotiations. These include discussions of a peace treaty or new security arrangement in the region, scaling back military exercises that the North sees as threatening, and selective easing of sanctions.

A verified ban on flight testing, of course, is just a step. The ultimate goal should be to stop further missile development and production at all levels, and to eliminate existing missiles—and that is what the United States should be working for. But that will require North Korea to feel secure enough to agree to these steps, which would include intrusive verification measures. That is not going to happen overnight and will require reciprocal steps by the United States.

It’s worth noting that the United States has had a lot of hands-on experience with verifying the elimination and non-production of missiles over the past 30 years through the verification measures of the INF Treaty, which it recently announced it was leaving.

What about Reports that North Korea is Continuing to Build Up its Missile Sites?

North Korea has taken several steps that are consistent with its statement about discontinuing nuclear and missile tests. In May 2018 it destroyed the entrances and some of the tunnels at its nuclear test site. In July it dismantled some facilities at one of its main missile test sites. While these steps were done without international inspectors present and could be reversed, they are interesting steps that are consistent with a willingness to end testing.

More recently there have been press reports of satellite images that show Korean missile bases that had not been publicly identified earlier, and show that North Korea has been continuing its ongoing work at some of these sites. These send a different message.

But these reports shouldn’t derail negotiations. It’s useful to have more information about these sites as part of the public discussion, but it’s important to recognize that these “secret” sites have long been known and are being monitored by US intelligence.

Moreover, there is nothing in the negotiations so far that has obligated Pyongyang to stop work on these bases or dismantle them. Working to get agreement on such steps is an important goal for the upcoming summit. If the United States sees those steps as important, it should decide what it is willing to put on the table to get them.

There have been 18 intercept flight tests of the Ground-based Missile Defense (GMD) system through 2018. Contrary to some claims, these tests have not demonstrated that the missile defense system would be successful in intercepting incoming warheads under realistic conditions.

The primary purpose of the tests has been to demonstrate “hit to kill,” that is, to test the ability of the missile defense kill vehicle to home on the target warhead and physically collide with it. Yet the system has succeeded in doing this in only half the tests overall, and only 40 percent of the latest 10 tests, so the record is not improving.

Moreover, none of these tests have included realistic decoys and other countermeasures that the system would be expected to face in a real attack—including an attack from North Korea. So the effectiveness of the defense against a real-world attack would be even lower than the 40 to 50 percent seen in the tests.

Fig 1. The balloon decoy used in early tests appeared about six times brighter than the reentry vehicle to the kill vehicle’s sensor and was therefore easy to distinguish (Source: UCS)

Some of the 18 intercept tests have included decoy balloons to test whether the kill vehicles can distinguish the mock warhead from other objects. However:

• The decoy balloons and other objects used in the tests have been designed to look very different than the warhead, so have been easy to distinguish;
• Information about the different appearance of the objects is given to the kill vehicle in advance, so that it can recognize which object is which;
• Decoys that prove difficult for the kill vehicle to distinguish have not been used in subsequent tests.

This new analysis (and summary) discusses each of the GMD intercept tests and describes the decoys used in each of them.

What this makes clear is that the GMD tests have not demonstrated the ability of the GMD system to successfully discriminate objects the kill vehicle might see in a real-world attack.

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The idea of space-based missile defense system has been around for more than 30 years. There are at least two reasons for its continuing appeal.

The first is that it is seen as a global system that could defend against missile launches from anywhere in the world.

The second is the attraction of intercepting long-range ballistic missiles during their “boost phase”—the few minutes when their engines are burning. Hitting a missile while it is burning sidesteps the difficulty of evading decoys and other countermeasures that missiles can release during midcourse phase after their engines shut off. Defenses that are intended to intercept during midcourse phase, like the US Ground-based Midcourse Defense and Aegis systems, are highly susceptible to countermeasures.

But for an interceptor to be able to reach a missile during the short boost phase, it must be stationed close to where the missile is launched—which is the motivation for putting interceptors in orbit so they can pass over the launch site.

However, the reality of space-based defenses is not so appealing.

Technical studies (for example, by the American Physical Society (APS) (2004) and National Academies of Science and Engineering (2012)) show that even a system with many hundreds of space-based interceptors would not provide an effective defense—in part because the interceptor constellation would be vulnerable to anti-satellite weapons and to being overwhelmed by a salvo of missile launches.

Yet it would be extremely expensive. The National Academy study concluded that a space-based boost-phase missile defense would cost 10 times more than any terrestrial alternative. It said that even an “austere and limited-capability” system would cost at least $300 billion.

These problems are intrinsic to the system because of the physics of operating in space. A few diagrams can make clear why—see below.

Basics, and Implications

The technology does not exist for space-based lasers powerful enough for missile defense, so the defense systems being discussed would use kinetic interceptors that would accelerate out of orbit and physically collide with a missile. Since a missile’s boost phase lasts only a few minutes, in order to reach the missile the interceptors need to be in low-altitude orbits (typically 300 to 500 km (200 to 300 miles)) that pass over the launch site.

Fig. 1. An orbit lies in a plane that passes through the center of the Earth. The angle between that plane and the plane that contains the equator is called the “inclination” of the orbit. The “ground track” of an orbit is the line of points on the Earth directly below the satellite. (Source)

The fact that the interceptors are in low-altitude orbits has three important implications:

1. The system needs a very large number of interceptors in orbit: An interceptor can’t sit over one location on Earth (the orbit that allows satellites to appear stationary over a point on the ground is 100 times higher—in the geostationary band—which is much too far away). Instead, to remain in orbit the interceptor constantly moves at very high speed (25 times the speed of a jet); at this speed it circles the Earth in about 90 minutes. As a result, it spends very little time over any particular spot on the Earth.

That means the system needs many interceptors in orbit so that one moves into position as the one in front of it moves out of position. As I show below, 300 to 400 interceptors are needed in orbit just to cover North Korea, and 1,000 or more for global defense coverage.

2. An adversary will know where the interceptors are at all times: At these low altitudes, the interceptors can be easily tracked by an adversary, who can then calculate where they will be in the future since objects in orbit move in a predictable way. An adversary will therefore also know where there are any holes in the defense coverage. A defense with predictable holes in it is not an effective defense.

Fig. 2. Even a 1,200 km (750 mile) range missile could lift an anti-satellite weapon high enough to attack a space-based interceptor in a 300 to 500 km altitude orbit.

3. The interceptors will be vulnerable to attack from low-cost ground-based weapons: To launch objects into orbit you need to lift them to high altitude AND accelerate them to very high orbital speed. That requires a large space-launch rocket and is very expensive, which contributes to the high cost of creating a large constellation of interceptors in space.

However, firing an anti-satellite (ASAT) weapon at an interceptor as it passes overhead just requires lifting the ASAT to the altitude of interceptor, and that can be done with a relatively cheap short-range or medium-range missile. Interceptors orbiting at 300 to 500 km would easily be within range of the Chinese DF-21D missile. Figure 2 shows that even a missile like a North Korean Nodong or Iranian Shahab 3 fired vertically could reach high enough altitudes to attack these interceptors if these countries developed or acquired ASAT capability to put on them.

Estimating the Number of Space-based Interceptors to Cover North Korea

This section shows why the physics of space-based boost-phase interceptors requires such a large constellation.

For a system optimized to defend against launches from North Korea, a space-based interceptor would be in an orbit like the white one in Figure 3, which is inclined at 45^o to the equator and can carry the interceptor over North Korea.

Fig. 3. The white circle is the ground track of an interceptor orbit that is inclined at 45^o to the equator (red circle).

Figure 4 shows missile trajectories (yellow lines) from North Korea to the east and west coasts of the United States. The yellow circle shows the region in which a space-based interceptor traveling on the white orbit could intercept a missile below it. This circle is 1,600 km (1,000 miles) in diameter, which assumes a very capable interceptor in a low-altitude orbit against liquid-fueled missiles like North Korea has. Against solid-fueled missiles, which would typically have a shorter burn times, the circle would be smaller.

Fig. 4. The white curve is the ground track of the interceptor’s orbit. The yellow circle is the region in which the interceptor could reach a missile launched below it. The circle is 1,600 km in diameter, which assumes δV = 4 km/s for the interceptor, in line with the assumptions in the APS and National Academies studies.

The interceptor moves rapidly in orbit, circling the Earth in about 90 minutes. That means the yellow circle will only be over North Korea for 3.5 minutes. To keep an interceptor over North Korea at all times there must be other interceptors in the orbit (black dashed circles) that move into place when the ones in front of them move out of place (Fig. 5).

Fig. 5. As the interceptor moves in orbit, the yellow circle will not stay over North Korea and additional interceptors—indicated here by the black dashed circles—must be in position to take its place.

To have constant coverage over North Korea, there must be interceptors all around the orbit. In the case shown here, it takes 25 interceptors to fill up this orbit so that one of them is always over some part of North Korea. Since you would want overlap between the circles, you would need more than that—probably 40 to 50 interceptors in the orbit.

So far we have taken into account the motion of the interceptor in its orbit but not the fact that the Earth is rotating under this orbit. Three and a half hours after the situation shown in Figure 5 North Korea will have moved 4,000 km (2,500 miles) east. The interceptors on this orbit will no longer be able to reach missiles launched from North Korea: Figure 6 shows that the yellow circle no longer contains any part of the missile trajectories. That means the system would need seven or eight orbits spaced around the Earth, each with 40 to 50 interceptors, so that interceptors on these other orbits will be over North Korea as the Earth rotates.

Fig. 6. Three and a half hours later than the situation shown in Figure 5, the Earth will have rotated under the orbit and the interceptor in the yellow circle will no longer be able to reach missiles launched from North Korea toward the United States.

Figure 7 shows eight equally spaced orbits (white lines) for a constellation optimized to cover North Korea, with a total of 300 to 400 interceptor satellites. That constellation, however, would only give constant coverage over latitudes near North Korea (red dot). Below about 35^o latitude there would be big gaps in the coverage through which a country could fire a missile. And the constellation gives no coverage at all above about 55^o latitude, which includes almost all of Russia (Fig. 8).

Fig. 7. Eight orbits (white lines) making up a constellation to cover North Korea.

Fig. 8. This figure shows the ground coverage (gray areas) of interceptor satellites in a constellation using equally spaced orbital planes with 45° inclination, assuming the interceptors can defend an area 1,600 km in diameter. The two dark lines are the ground tracks of two of the interceptors in neighboring planes. As the gray areas show, this constellation can provide complete ground coverage for areas between about 30° and 50° latitude (both north and south), less coverage below 30°, and no coverage above about 55°.

Achieving more global coverage would require a constellation of 1,000 or more interceptor satellites. Figure 9 shows a constellation of 24 orbits with inclinations of 65^o. With 40 to 50 interceptor satellites per orbit, this system would have a total of 960 to 1,200 satellites.

Such a system would still only be able to engage a few missiles fired in a volley from the same place. It would give thin coverage at all latitudes between 70 degrees north and south, assuming a boost-phase interceptor that could defend an area shown by the yellow circle in Figure 2.

Fig 9. This figure shows a constellation of 24 orbits with inclinations of 65^o. With 40 to 50 interceptor satellites per orbit, this system would have a total of 960 to 1,200 satellites and could give thin coverage of the Earth between 70^o north and south latitude. The yellow circle is the area one interceptor could cover, which we assume is 1,600 km in diameter, as in Figures 4-6.

Two final notes:

1. It doesn’t make sense to put midcourse interceptors in space: midcourse interceptors do not need to be close to the launch site, and deploying them in space leads to a very expensive system compared to ground-based systems.
2. For a geographically small country bordered by water—in particular, North Korea—boost phase intercepts may be possible from from air-borne drones or ships, which are options currently being researched.

For more on space-based defenses, click here.

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Articles citing a classified 2011 report by the Institute for Defense Analysis (IDA) have mistakenly suggested the report finds that a constellation of only 24 satellites can be used for space-based boost-phase missile defense.

This finding would be in contrast to many other studies that have shown that a space-based boost-phase missile defense system would require hundreds of interceptors in orbit to provide thin coverage of a small country like North Korea, and a thousand or more to provide thin coverage over larger regions of the Earth.

A 2011 letter from Missile Defense Agency (MDA) Director Patrick O’Reilly providing answers to questions by then-Senator Jon Kyl clarifies that the 24-satelllite constellation discussed in the IDA study is not a boost-phase missile defense system, but is instead a midcourse system designed to engage anti-ship missiles:

The system discussed by IDA appears to be a response to concerns about anti-ship ballistic missiles that China is reported to be developing. It would have far too few satellites for boost-phase defense against missiles from even North Korea, and certainly from a more sophisticated adversary.

The MDA letter says the 24 satellites might carry four interceptors each. Adding interceptors to the satellites does not fix the coverage problem, however: If one of the four interceptors is out of range, all the interceptors are out of range, since they move through orbit together. As described below, the coverage of a space-based system depends on the number of satellites and how they are arranged in orbit, as well as the ability of the interceptors they carry to reach the threat in time.

While this configuration would place four interceptors over some parts of the Earth, it would leave very large gaps in the coverage between the satellites. An attacker could easily track the satellites to know when none were overhead, and then launch missiles through the gaps. As a result, a defense constellation with gaps would realistically provide no defense.

(The IDA report is “Space Base Interceptor (SBI) Element of Ballistic Missile Defense: Review of 2011 SBI Report,” Institute for Defense Analyses, Dr. James D. Thorne, February 29, 2016.)

Why boost phase?

The advantage of intercepting during a ballistic missile’s boost phase—the first three to five minutes of flight when its engines are burning—is destroying the missile before it releases decoys and other countermeasures that greatly complicate intercepting during the subsequent midcourse phase, when the missile’s warhead is coasting through the vacuum of space. Because boost phase is short, interceptors must be close enough to the launch site of target missiles to be able to reach them during that time. This is the motivation for putting interceptors in low Earth orbits—with altitudes of a few hundred kilometers—that periodically pass over the missile’s launch site.

The fact that the interceptors must reach a boosting missile with a few minutes limits how far the interceptor can be from the launching missile and still be effective. This short time therefore limits the size of the region a given interceptor can cover to several hundred kilometers.

An interceptor satellite in low Earth orbit cannot sit over one point on the Earth, but instead circles the Earth on its orbit. This means an interceptor that is within range of a missile launch site at one moment will quickly move out of range. As a result, having even one interceptor in the right place at the right time requires a large constellation of satellites so that as one interceptor moves out of range another one moves into range.

Multiple technical studies have shown that a space-based boost phase defense would require hundreds or thousands of orbiting satellites carrying interceptors, even to defend against a few missiles. A 2012 study by the National Academies of Science and Engineering found that space-based boost phase missile defense would cost 10 times as much as any ground-based alternative, with a price tag of $300 billion for an “austere” capability to counter a few North Korean missiles.

Designing the system instead to attack during the longer midcourse phase significantly increases the time available for the interceptor to reach its target and therefore increases the distance the interceptor can be from a launch and still get there in time. This increases the size of the region an interceptor can cover—up to several thousand kilometers (see below). Doing so reduces the number of interceptors required in the constellation from hundreds to dozens.

However, intercepting in midcourse negates the rationale for putting interceptors in space in the first place, which is being close enough to the launch site to attempt boost phase intercepts. Defending ships against anti-ship missiles would be done much better and more cheaply from the surface.

Calculation of Constellation Size

Figure 1 shows how to visualize a system intended to defend against anti-ship missiles during their midcourse phases. Consider an interceptor designed for midcourse defense on an orbit (white curve) that carries it over China (the red curve is the equator). If the interceptor is fired out of its orbit shortly after detection of the launch of an anti-ship missile with a range of about 2,000 km, it would have about 13 minutes to intercept before the missile re-entered the atmosphere. In those 13 minutes, the interceptor could travel a distance of about 3,000 km, which is the radius of the yellow circle. (This assumes δV = 4 km/s for the interceptor, in line with the assumptions in the National Academies of Science and Engineering study.)

The yellow circle therefore shows the size of the area this space-based midcourse interceptor could in principle defend against such an anti-ship missile.

Fig. 1.  The yellow circle shows the coverage area of a midcourse interceptor, as described in the post; it has a radius of 3,000 km. The dotted black circle shows the coverage area of a boost-phase interceptor; it has a radius of 800 km.

However, the interceptor satellite must be moving rapidly to stay in orbit. Orbital velocity is 7.6 km/s at an altitude of 500 km. In less than 15 minutes the interceptor and the region it can defend will have moved more than 6,000 km along its orbit (the white line), and will no longer be able protect against missiles in the yellow circle in Figure 1.

To ensure an interceptor is always in the right place to defend that region, there must be multiple satellites in the same orbit so that one satellite moves into position to defend the region when the one in front of it moves out of position. For the situation described above and shown in Figure 1, that requires seven or eight satellites in the orbit.

At the same time, the Earth is rotating under the orbits. After a few hours, China will no longer lie under this orbit, so to give constant interceptor coverage of this region, there must be interceptors in additional orbits that will pass over China after the Earth has rotated. Each of these orbits must also contain seven or eight interceptor satellites. For the case shown here, only two additional orbits are required (the other two white curves in Figure 1).

Eight satellites in each of these three orbits gives a total of 24 satellites in the constellation to maintain coverage of one or perhaps two satellites in view of the sea east of China at all times. This constellation and could therefore only defend against a small number of anti-ship missiles fired essentially simultaneously. Defending against more missiles would require a larger constellation.

If the interceptors are instead designed for boost-phase rather than midcourse defense, the area each interceptor could defend is much smaller. An interceptor with the same speed as the one described above could only reach out about 800 km during the boost time of a long-range missile; this is shown by the dashed black circle in Figure 1.

In this case, the interceptor covering a particular launch site will move out range of that site very quickly—in about three and a half minutes. Maintaining one or two satellites over a launch site at these latitudes will therefore require 40 to 50 satellites in each of seven or eight orbits, for a total of 300 to 400 satellites.

The system described—40 to 50 satellites in each of seven or eight orbits—would only provide continuous coverage against launches in a narrow band of latitude, for example, over North Korea if the inclination of the orbits was 45 degrees (Fig. 2). For parts of the Earth between about 30 degrees north and south latitude there would be significant holes in the coverage. For areas above about 55 degrees north latitude, there would be no coverage. Broader coverage to include continuous coverage at other latitudes would require two to three times that many satellites—1,000 or more.

As discussed above, defending against more than one or two nearly simultaneous launches would require a much larger constellation.

Fig. 2. The figure shows the ground coverage (gray areas) of interceptor satellites in seven equally spaced orbital planes with inclination of 45°, assuming the satellites can reach laterally 800 km as they de-orbit. The two dark lines are the ground tracks of two of the satellites in neighboring planes. This constellation can provide complete ground coverage for areas between about 30° and 50° latitude (both north and south), less coverage below 30°, and no coverage above about 55°.

For additional comments on the IDA study, see Part 2 of this post.

1. Vulnerability of missile defense satellites to anti-satellite (ASAT) attack

To be able to reach missiles shortly after launch, space-based interceptors (SBI) must be in low-altitude orbits; typical altitudes discussed are 300 to 500 km. At the low end of this range atmospheric drag is high enough to give very short orbital lifetimes for the SBI unless they carry fuel to actively compensate for the drag. That may not be needed for orbits near 500 km.

Interceptors at these low altitudes can be easily tracked using ground-based radars and optical telescopes. They can also be reached with relatively cheap short-range and medium-range missiles; if these missiles carry homing kill vehicles, such as those used for ground-based midcourse missile defenses, they could be used to destroy the space-based interceptors. Just before a long-range missile attack, an adversary could launch an anti-satellite attack on the space-based interceptors to punch a hole in the defense constellation through which the adversary could then launch a long-range missile.

Alternately, an adversary that did not want to allow the United States to deploy space-based missile defense could shoot space-based interceptors down shortly after they were deployed.

The IDA report says that the satellites could be designed to defend themselves against such attacks. How might that work?

Since the ASAT interceptor would be lighter and more maneuverable than the SBI, the satellite could not rely on maneuvering to avoid being destroyed.

A satellite carrying a single interceptor could not defend itself by attacking the ASAT, for two reasons. First, the boost phase of a short- or medium-range missile is much shorter than that of a long-range missile, and would be too short for an interceptor designed for boost-phase interception to engage. Second, even if the SBI was designed to have sensors to allow intercept in midcourse as well as boost phase, using the SBI to defend against the ASAT weapon would remove the interceptor from orbit and the ASAT weapon would have done its job by removing the working SBI from the constellation. A workable defensive strategy would require at least two interceptors in each position, one to defend against ASAT weapons and one to perform the missile defense mission.

The IDA report assumes the interceptor satellites it describes to defend ships would each carry four interceptors. If the system is meant to have defense against ASAT attacks, some of the four interceptors must be designed for midcourse intercepts. The satellite could carry at most three such interceptors, since at least one interceptor must be designed for the boost-phase mission of the defense. If an adversary wanted to punch a hole in the constellation, it could launch four ASAT weapons at the satellite and overwhelm the defending interceptors (recall that the ASAT weapons are launched on relatively cheap short- or medium-range missiles).

In addition, an ASAT attack could well be successful even if the ASAT was hit by an interceptor. If an interceptor defending the SBI hit an approaching ASAT it would break the ASAT into a debris cloud that would follow the trajectory of the original center of mass of the ASAT. If this intercept happened after the ASAT weapon’s course was set to collide with the satellite, the debris cloud would continue in that direction. If debris from this cloud hit the satellite it would very likely destroy it.

2. Multiple interceptors per satellite

It is important to keep in mind that adding multiple interceptors to a defense satellite greatly increases the satellite’s mass, which increases its launch cost and overall cost.

The vast majority of the mass of a space-based interceptor is the fuel needed to accelerate the interceptor out of its orbit and to maneuver to hit the missile (the missile is itself maneuvering since it is during its boost phase, when it is accelerating and steering). For example, the American Physical Society’s study assumes the empty kill vehicle of the interceptor (the sensor, thrusters, valves, etc) is only 60 kg, but the fueled interceptor would have a mass of more than 800 kg.

Adding a second interceptor to the defense satellite would add another 800 kg to the overall mass. A satellite with four interceptors and a “garage” that included the solar panels and communication equipment could have a total mass of three to four tons.

3. Space debris creation

Senator Kyl asked the MDA to comment on whether space-based missile defense would create “significant permanent orbital debris.” The MDA answer indicated that at least for one mechanism of debris creation (that of an intercept of a long-range missile), the system could be designed to not generate long-lived debris.

However, there are at least three different potential debris-creating mechanisms to consider:

• Intercepting a missile with an SBI

When two compact objects collide at very high speed, the objects break into two expanding clouds of debris that follow the trajectories of the center of mass of the original objects. In this case the debris cloud from the interceptor will likely have a center of mass speed greater than Earth escape velocity (11.2 km/s) and most of the debris will therefore not go into orbit or fall back to Earth. Debris from the missile will be on a suborbital trajectory; it will fall back to Earth and not create persistent debris.

• Using an SBI as an anti-satellite weapon

If equipped with an appropriate sensor, the space-based interceptor could home on and destroy satellites. Because of the high interceptor speed needed for boost phase defense, the SBI could reach satellites not only in low Earth orbits (LEO), but also those in semi-synchronous orbits (navigation satellites) and in geosynchronous orbits (communication and early warning satellites). Destroying a satellite on orbit could add huge amounts of persistent debris to these orbits.

At altitudes above about 800 km, where most LEO satellites orbit, the debris from a destroyed satellite would remain in orbit for decades or centuries. The lifetime of debris in geosynchronous and semi-synchronous orbits is essentially infinite.

China’s ASAT test in 2007 created more than 3,000 pieces of debris that have been tracked from the ground—these make up more than 20% of the total tracked debris in LEO. The test also created hundreds of thousands of additional pieces of debris that are too small to be tracked (smaller than about 5 cm) but that can still damage or destroy objects they hit because of their high speed.

Yet the satellite destroyed in the 2007 test had a mass of less than a ton. If a ten-ton satellite—for example, a spy satellite—were destroyed, it could create more than half a million pieces of debris larger than 1 cm in size. This one event could more than double the total amount of large debris in LEO, which would greatly increase the risk of damage to satellites.

• Destroying an SBI with a ground-based ASAT weapon

As discussed above, an adversary might attack a space-based interceptor with a ground-based kinetic ASAT weapon. Assuming the non-fuel mass of the SBI (with garage) is 300 kg, the destruction of the satellite could create more than 50,000 orbiting objects larger than 5 mm in size.

If the SBI was orbiting at an altitude of between 400 and 500 km, the lifetime of most of these objects will be short so this debris would not be considered to be persistent. However, the decay from orbit of this debris would result in an increase in the flux of debris passing through the orbit of the International Space Station (ISS), which circles the Earth at an altitude of about 400 km. Because the ISS orbits at a low altitude, it is in a region with little debris since the residual atmospheric density causes debris to decay quickly. As a result, the additional debris from the SBI passing through this region can represent a significant increase.

In particular, if the SBI were in a 500-km orbit, the destruction of a single SBI could increase the flux of debris larger than 5 mm at the altitude of the ISS by more than 10% for three to four months (at low solar activity) or two to three months at high solar activity. An actual attack might, of course, involve destroying more than one SBI, which would increase this flux.

What should we make of this?

Pyongyang said it would allow journalists from the United States, Russia, Britain, and South Korea to watch the destruction of the tunnels at Punggye-ri sometime in the coming week (May 23-25). These tunnels dug into the mountain are where North Korea conducts its nuclear tests. US intelligence says that North Korea is already dismantling the test site, and satellite photos of the site (here and here) confirm that a number of facilities at the site have already been torn down.

Punggye-ri Test Site (Source: Google Earth)

If North Korean leader Kim Jong-un is serious about limiting and perhaps eventually eliminating his nuclear and missile capabilities in return for economic engagement with the outside world, the question is how he demonstrates that seriousness. Publicly shutting down his test site is a meaningful step in the right direction and an interesting way to try to send that message.

It’s true that shutting down the Punggye-ri test site does not prevent North Korea from ever testing again. If negotiations fail or situations change in the future, it could decide to tunnel at a different site and build the required infrastructure needed to test. But it’s a meaningful and pretty dramatic action nonetheless.

For one thing, while part of the current test site is no longer usable because some tunnels collapsed after previous tests, experts agree that a couple tunnels at the site remain usable. They also agree that disabling the facilities would take time to reverse—perhaps months or longer.

This reminds me of North Korea’s decision in 2008 to disable its nuclear reactor at Yongbyon by  blowing up the cooling tower and letting foreign reporters film the event. This was at a time when negotiations with the United States seemed to be moving ahead. A few years later after negotiations had stalled, Pyongyang built a new cooling system and was able to restart the reactor. But disabling the reactor was still a meaningful action, since it kept the reactor from operating for several years.

What’s next?

North Korea’s statements last week raised the possibility that Kim was walking back his various offers. Yet Kim’s criticism was focused on statements by John Bolton and others about the need for the North to denuclearize as an early step of negotiations. This is an approach Pyongyang has consistently rejected, calling instead for a step-by-step process that helps build the trust needed for additional steps.

President Trump’s subsequent statement disavowing this so-called “Libyan model” of disarmament seemed intended to help repair the situation, but his later statement that appeared to threaten destruction of North Korea if talks failed could have exactly the opposite effect and lead Kim to cancel or delay the talks. In the meantime, China has urged Pyongyang to continue with the talks.

So whether or not the summit will proceed as planned remains uncertain. An important indicator will be whether North Korea goes ahead with destroying tunnels at its test site this week.

Kim has talked about the dual goals of security and improving the economy. A key goal of early talks should be for the United States to understand what North Korea wants and what it is willing to do to get those things.

(Source: KCNA)

Kim’s first interest is likely setting up conditions that assure the survival of his regime without needing nuclear weapons. Recent press reports indicated what steps North Korea sees as important to increase its security, including:

• stopping the inclusion of “nuclear and strategic assets” during US joint military exercises with South Korea,
• guaranteeing that the United States will not attack North Korea with either conventional or nuclear weapons,
• converting the armistice agreement from the Korean War into a peace treaty, and
• normalizing diplomatic relations with the United States.

As part of normalizing relations, the United States should discuss opening a liaison office in Pyongyang, and to have North Korea do so in the United States. This step was discussed in the 1990s and was expected to occur by the end of 1998, but never happened.

As noted in Part 1 of this post, North Korea stated in 2016 that denuclearization “includes the dismantlement of nukes in South Korea and its vicinity.” The United States will need to understand what it means by “its vicinity,” and whether Pyongyang sees that as including the US air base on Guam, where nuclear-capable bombers are based, or Okinawa, where nuclear storage sites may be built as part of a new US military base there.

Non-military issues

In addition to security measures, North Korea is also looking for economic and development assistance. As in past negotiations this assistance would not all come from the United States.

One step would clearly be relaxing sanctions. A second would be to remove North Korea from the list of state sponsors of terrorism. President Bush had removed it from the list in 2008, but President Trump relisted it last November. This creates a barrier, for example, to economic assistance and getting loans from the World Bank and other international institutions.

In the past there were discussions of helping North Korea grow more of its own food through assistance with fertilizer, measures to repair and improve irrigation systems, etc. Such assistance would still be important.

In past negotiations there has also been a focus on energy assistance. Frequently that took the form of shipments of heavy fuel oil, which was chosen because it could be used to produce energy but was not highly refined enough to be useful to fuel military vehicles, etc. However, its interest is certainly broader than that. In the 1990s, North Korea was interested in assistance in developing energy technologies, including sending scientists to the National Renewable Energy Laboratory. The North could also benefit from assistance in modernizing its power grid.

In the past, North Korea has also declared the right to develop nuclear energy for peaceful uses, and is currently building a reactor that it says is intended for producing power and would not be used for military purposes. In principle, this could be done once it has rejoined the NPT and allowed the IAEA to safeguard its nuclear facilities, but given North Korea’s past action in expelling inspectors and pulling out of the NPT this is certain to be controversial.

North Korea has also been interested in assistance to improve its mining sector. Such a step could be very important since minerals are one of the main resources North Korea has to earn foreign exchange. A recent article notes that

North Korea has sizeable deposits of more than 200 different minerals, including coal, iron ore, magnesite, gold ore, zinc ore, copper ore, limestone, molybdenite, graphite and tungsten. All have the potential for the development of large-scale mines.

The United States could help establish a fund to assist North Korea in developing its mining technology and infrastructure, and could encourage private capital to help develop the mining sector. In 1993, Israel was negotiating with North Korea to stop missile sales to the Middle East, and assistance for its mining industry was an important part of the deal. Ultimately, Israel backed away from this agreement under US pressure since the United States was negotiating with North Korea over its nuclear program at the time.

Former Senators Nunn and Lugar have also proposed developing a program that would help employ and retrain scientists and engineers from North Korea’s military sector, and to provide technical and financial assistance for destroying and disposing of nuclear, chemical, and biological weapons and their delivery systems. This is similar to what was done under the successful Cooperative Threat Reduction program Nunn and Lugar developed after the breakup of the Soviet Union.

Finally, North Korea has stated that it wants to be able to use space in the ways other countries do—for communications, earth monitoring, resource exploration, weather forecasts, etc.—and has developed an incipient satellite launch capability. An indigenous satellite launch program could be acceptable sometime in the future when the international community has developed more trust in the North Korean regime, but not in the near term.

There are several approaches to negotiating an end to this program. One approach is for the international community to provide North Korea access to various kinds of satellite services and help with developing the expertise needed to use it, eliminating the need for it to own and operate its own satellites.

A second approach would be to set up a consortium that could help North Korea develop technical satellite expertise and design and build a satellite. The international community would then fund or heavily subsidize foreign launch services to compensate for North Korea’s lack of domestic launch capability. And in either case it could be useful to integrate North Korea into various international and regional space and satellite forums.

(Part 1 of this post)

(Source: KCNA)

Beginning talks

The current situation seems to offer about as good a stage as one can imagine for talks that could lead to meaningful changes in North Korea’s nuclear and missile programs.

In particular, North Korea has said it is willing to talk about denuclearization, which is a long-standing US pre-condition for talking. Press reports in early April reported that Pyongyang had repeated its willingness to discuss denuclearization and indicated the key things it wanted in return, which are steps to increase the security of the regime that appear similar to steps the United States agreed to under the Bush administration. And it has said it would not require US forces to leave South Korea as part of such a deal.

Moreover, North Korea has said it is ending nuclear and missile tests. It has not conducted a missile test in more than four months—which is especially noteworthy after testing at a rate of nearly twice a month in 2017. A lack of testing is meaningful since it places significant limits on North Korea’s development of nuclear weapons and long-range missiles, and it can be readily verified by US satellites and seismic sensors in the region.

There is a debate about whether “denuclearization” is a realistic long-term goal of negotiations, what that term means to North Korea, and what it would take to get North Korea to give up its weapons. It seems significant, however, that in July 2016 Pyongyang stated that denuclearization means “denuclearization of the whole Korean peninsula and this includes the dismantlement of nukes in South Korea and its vicinity” but did not say it would only give up its weapons when the United States and other countries disarm, which is the position it had taken previously.

Whether or not full denuclearization of the peninsula is possible, there is a lot to be done in the near-term that would greatly benefit US and regional security and set the conditions for denuclearization.

And the administration should remember that the alternatives to diplomacy are not good: The best is a stalemate in which the United States uses the threat of retaliation to deter a North Korean strike, just as it does with Russia and China. A military strike and response by North Korea would be a disaster for the region.

Confrontation vs. Diplomacy

The first thing the administration must decide is whether it will pursue confrontation or diplomacy in this meeting.

There is a strong feeling among some in Washington that the North Korean regime is evil and that any effort to negotiate simply helps the regime—and that the United States should not be doing that. Instead these people believe the only solution is regime change in Pyongyang. They see a face-to-face meeting at best as an opportunity to confront North Korea rather than seriously negotiate.

This issue will certainly become a prominent point debated in Washington if negotiations go forward. If President Trump wants an agreement he will have to ignore these arguments, which torpedoed negotiations under the Bush administration.

Even among those in the administration who want to engage North Korea, the prevailing idea seems to be that the United States should demand that North Korea give the United States what it wants up front before Washington will reciprocate.

For example, in his recent confirmation hearing for secretary of state, Mike Pompeo said the administration would not give North Korea “rewards” until it had denuclearized “permanently, irreversibly.” Similarly, an unnamed administration official said “the US will not be making substantial concessions, such as lifting sanctions, until North Korea has substantially dismantled its nuclear programs.”

Because of the long-standing lack of trust between the two countries, North Korea has instead called for a “phased, synchronized” implementation of any deal. This is the approach adopted at the Six Party talks in 2005, when the parties agreed to move forward “commitment for commitment, action for action.” Kim presumably wants a step-by-step process that convinces him that he will not become the next Gadhafi.

These US statements may still allow Washington to offer things early on other than sanctions relief, such as taking steps to normalize relations and remove North Korea from the list of state sponsors of terrorism. If instead the administration expects North Korea to give the United States what it wants up front—and lose its negotiating leverage before the United States addresses the issues Pyongyang brings to the table—that approach will fail.

One concern is that the United States may overestimate the leverage it has, overplay its hand at the table, and lead to a failed summit. If other countries see an intransigent US approach as preventing progress on engaging North Korea and reducing the risk it poses, that could begin to create cracks in the sanctions regime, which would reduce US leverage for substantial changes.

It’s worth remembering that in the early 2000s the George W Bush administration’s confrontation policy derailed negotiations that appeared close to ending Pyongyang’s plutonium production and missile development at a time North Korea had no nuclear weapons or long-range missiles. Following that, North Korea continued these programs and today it has both.

What is North Korea up to?

Why the new tone from Pyongyang and the limits it has announced on its nuclear and missile programs?

Some suggest this is just a ploy by North Korea to buy time to produce more fissile material and missile parts, and to try to create splits between the countries currently supporting sanctions against it with the hope of getting sanctions relief without really limiting its military capabilities in a serious way.

On the other hand, it may be that Kim understands his military buildup is unsustainable and that to stay in power he needs to turn to improving the economy, as he promised when he took power. Nicholas Kristof wrote recently that “Kim has made rising living standards a hallmark of his leadership, and sanctions have threatened that pillar of his legitimacy.” Now that he appears to feel secure with his position within the ruling elite he may need to think about the middle class that appears to be emerging in North Korea.

He may have decided, as his father appeared to in the late 1990s, that opening to the world is his only chance for real economic growth. Not only are his nuclear and missile programs barriers to that opening, they are also two of the few things of significant value he has to take to the negotiating table.

That doesn’t mean he has decided to get rid of them any time soon. But if this is his thinking, then significantly limiting—and possibly eventually eliminating—these programs makes sense if he can get security assurances that convince him he doesn’t need these weapons.

To understand what it is dealing with, the United States will have to take steps that test to what extent the North is willing to accept meaningful limitations—such as accepting international inspectors to confirm that plutonium production and uranium enrichment facilities are shut down and beginning to be dismantled. This has happened before with North Korea’s nuclear facilities at Yongbyon, so there is a precedent. These steps are important both for understanding Pyongyang’s intent and for halting its nuclear program on the way to denuclearization.

Near-term goals

The best outcome for a meeting between the two leaders is that it will set broad goals for an agreement that addresses both countries’ security concerns and establishes a path to denuclearization. But as we’ve seen in the past, working out the details—especially on issues like inspections and verification—will be tricky and take time. So one goal of the first meeting should be to agree to a schedule of ongoing talks to give both countries an expectation of a continuing process, and a list of what issues will be on the table at future meetings.

Here are three things that should be near-term goals of the negotiations:

1. Locking in a permanent ban on nuclear and missile tests, and satellite launches.

(Source: KCNA)

North Korea has announced that it is ending nuclear and missile tests and shutting down its nuclear test site. The United States should clarify the details and get it written down as a formal commitment.

While North Korea put this on the table even before negotiations began, people should not overlook its potential importance.

North Korea has now done a single test of a missile that in principle can reach all of US territory, several underground tests of an atomic bomb, and a single underground test of what was likely a hydrogen bomb. Given those tests, North Korea can say it has—in principle at least—the ability to hit the United States with a nuclear missile and therefore has a deterrent to a US military attack.

Indeed, in his New Years’ message this year, Kim said, “we achieved the goal of completing our state nuclear force in 2017,” adding that “the entire area of the US mainland is within our nuclear strike range, and the US can never start a war against me and our country.”

But North Korea does not yet have a fully tested capability to attack the United States with a long-range missile, and this matters. With only a single test of its Hwasong-15 missile on a lofted trajectory and no known successful test of a reentry vehicle on a long-range missile, additional tests are necessary to gain that practical capability. Similarly, after only a single test of a hydrogen bomb, it is very unlikely North Korea has a design that is small and light enough to launch on a missile, and it has little information about the reliability of the design.

This means that stopping additional nuclear and missile tests is important and meaningful. And since the United States can verify that no tests are occurring, it will know if North Korea is abiding by the agreement.

There are reasons why Kim may be happy to stop testing long-range missiles at this point. For one thing, while his single test of the Hwasong-15 missile was successful, there is no guarantee that a second test would be. A failure would undercut Kim’s claim of having a missile capability against the United States.

Moreover, gaining confidence in the missile performance would require a series of successful flight tests. The rapid increase in the range of the tested missiles during 2017 may have been possible because key components were acquired from Russia. If so, the North may be limited in how many missiles it can actually build—either to test or put in an arsenal.

While I have argued that developing a working reentry vehicle is not likely to be a technical barrier for North Korea, it has not yet demonstrated that it has one in hand for a long-range missile. Stopping further missile tests would keep it that way.

The two countries should clarify what missiles the flight ban applies to. The United States should press for it to include all missiles—ballistic and cruise—that would have a range over 300 km with a 500 kg payload, which is the MTCR limit. It would therefore apply to missiles that could reach Japan. South Korea has developed ballistic missiles with ranges up to 800 km and cruise missiles with ranges up to 1,500 km, and this flight ban would apply to the South as well. That would require South Korea’s agreement to this limit.

The United States should make clear that the ban also applies to satellite launchers. Because the technologies for satellite launchers can be used to develop long-range missiles, stopping this development is an important part of ending its missile program. Getting the North to agree to give up that program, given the civil benefits of a satellite program, is likely to require the US to arrange for the international community to provide access to space launch or satellite services in place of a domestic space launch program.

A longer term step would be eliminating all missiles on the peninsula that fall under the flight ban. Verifying elimination would be more difficult than verifying a flight ban, but was discussed in the negotiations with North Korea under both Clinton and Bush, and verification was put in place as part of the Intermediate Nuclear Forces (INF) Treaty, which eliminated all US and Russia ground-based missiles with ranges between 500 and 5,500 km.

Following that, the next step could be to eliminate all missiles, as well as the artillery North Korea has aimed at Seoul, as part of a broader agreement limiting conventional forces.

2. A freeze on the production of separated plutonium and highly enriched uranium, leading to a ban

Yongbyon reactor (Source: US Senate)

A second near-term goal of negotiations should be an agreement to shut down North Korea’s nuclear reactors, which are the source of its plutonium, and have inspectors on the ground to ensure it does not extract plutonium from fuel rods that have been removed from the reactors. North Korea agreed to both steps in the 1994 Agreed Framework and verifiably did so until the Framework collapsed in 2002.

The agreement should also put international inspectors at North Korea’s known enrichment facility to verify that it is not being operated, and allow challenge inspections of other sites that it might suspect are being used for enrichment.

Getting these agreements would not be unprecedented. During the 2005 negotiations, Pyongyang agreed to “abandoning all nuclear weapons and existing nuclear programs and returning, at an early date, to the Treaty on the Nonproliferation of Nuclear Weapons and to IAEA safeguards.” Those negotiations eventually stalled over disagreements on verification measures and inspections, which were unresolved when the Bush administration left office.

The agreement should also require Pyongyang to preserve information that in the future would allow the IAEA to construct a history of its past nuclear activities. This would allow the IAEA to determine how much fissile material North Korea had produced—and whether it was all accounted for.

As part of the Six Party talks under George W. Bush in 2008, North Korea shut down its reactor at Yongbyon and provided 18,000 documents about its plutonium production, so there is a precedent for this as well.

3. A ban on the sale or transfer of missile or nuclear technology, or technical assistance

As part of a deal, North Korea should agree to a ban on the sale or transfer of missile or nuclear technology to other countries or groups, and a ban on providing technical assistance on these systems. Such a ban would require agreement on transparency measures to help provide confidence that such activities were not taking place. In a recent speech, Kim stated:

… the DPRK will never use nuclear weapons nor transfer nuclear weapons or nuclear technology under any circumstances unless there are nuclear threats and nuclear provocations against the DPRK.

So this could be a starting point for a discussion of these issues.

In the longer term, in addition to talking about denuclearization, the United States should focus on getting rid of North Korea’s chemical and biological weapons programs, and put restrictions on its conventional weapons. The latter would have to include restrictions on South Korean conventional weapons as well.

(The second part of this post will discuss what North Korea is likely to want from the talks.)

Checking Trump’s impulses

Source: CIA

As former CIA Director Michael Hayden noted, “Secretary Tillerson was a counterweight to some of the instantaneous, spontaneous, instinctive decisions that the president was prone to make. And I think we’re going to miss the counterweight.”

A key concern is Trump’s impulses on international affairs. He has focused heavily on military power and has shown a clear disregard for international agreements and for the importance of maintaining close relations with US allies.

Tillerson was a strong voice against pulling out of the Paris climate accords and the Iran nuclear deal. Tillerson also argued that it was important to maintain US credibility as a negotiating partner, both regarding past agreements and the possibility of future negotiations with North Korea.

He and others, including the general who commands US forces in the Middle East and Central Asia, argued that the Iran deal is not perfect—it was the result of a negotiation, after all—but the United States is better off with the deal than without it.

In contrast, Pompeo’s worldview is very similar to Trump’s, which may embolden Trump to act on his impulses.

This issue is even more important now that John Bolton is to become Trump’s national security advisor, since he seems likely to encourage some of Trump’s most dangerous impulses.

The future of the Iran Deal

 Pompeo has echoed Trump’s view of the Iran nuclear deal, calling it “disastrous” and saying he wants to see it ended.

And that could happen soon. Trump has said he will reimpose economic sanctions on Iran in mid-May if the other partners to the accord don’t agree to take steps to “fix the terrible flaws” of the deal. That seems unlikely to happen.

Pompeo’s disdain for the deal, and for diplomacy more generally, is clear. As a congressman, he was one of a group of people—including John Bolton—who advocated stopping the negotiations with Iran and instead bombing its nuclear facilities. In a 2014 meeting with reporters, he told them this could be done with “under 2,000 sorties” and that “This is not an insurmountable task for the coalition forces.”

Scuttling the deal would be a disaster. It would end the current strict limits and intrusive verification on Iran’s nuclear capabilities. It would also sow discord with a number of our close allies, who remain committed to the deal, and likely enflame anti-US sentiment in the region. It would also undermine US credibility on future negotiations.

Negotiations with North Korea

The credibility issue is important as the United States moves toward talks with North Korea about its nuclear and missile programs.

North Korean leader Kim Jong-Un recently offered to meet with Trump, who jumped at the opportunity. This is significant since Pyongyang said it is willing to talk about denuclearization, which is a long-standing US pre-condition for talking.

Moreover, the North said it will halt nuclear and missile tests while talks continue. Since the testing freeze can be readily verified, this is an important step: It means the freeze verifiably stops testing and gives ongoing evidence that North Korea is serious about the talks. This sets about as good a stage as one can imagine for talks that could lead to meaningful changes in North Korean nuclear and missile programs.

But how much will Pyongyang be willing to put on the negotiating table if it sees the United States walk away from the Iran deal despite international inspectors confirming that Iran is carrying out its side of the bargain?

And once talks start, will the US approach be negotiation or confrontation? Who at a high level in the administration is supporting diplomacy?

Pompeo advocates regime change in North Korea. As with Iran, his statements on North Korea seem to support military action against the country—something Bolton argued in favor of as recently as last month.

The administration has ramped up international sanctions against the country. Is it willing to negotiate an easing of sanctions for steps that lower hostility between the two countries and pave the way toward further steps? Or will it demand the North “denuclearize” before it is willing to reward its behavior? If the US does not negotiate seriously, but instead uses the talks as a forum to castigate Pyongyang for bad behavior, it will throw away an important opportunity and reignite hostilities.

The wrong choice

The United States needs a secretary of state who is a strong supporter of diplomacy as a means of improving US security. Mike Pompeo is not that person.

The Senate should reject his nomination and insist that the president choose someone who respects the benefits of diplomacy, which is a vital component of US security.

In the last week, North Korean leader Kim Jong-Un has continued to channel the good cop side of his personae, which started with his New Year’s Day offer to take part in the South Korean Olympics. Yesterday, the White House announced that it had received an offer from the North for President Trump to meet with Kim in the next two months to talk about security and nuclear weapons—a proposal the White House accepted.

This situation offers reasons for both optimism and concern.

On the one hand, Kim has offered to engage with the United States and talk about denuclearization, which the US has insisted on, and to suspend nuclear and missile tests during any talks. These steps help reduce the current tensions between the two countries that have led to fears that the Trump administration would attempt a preemptive military strike on North Korea—which could lead to devastating conflict in the region.

Moreover, having a high-level summit with Kim is likely the best way to make progress on these issues with a country that is built around top-down leadership. We have seen important progress in negotiations in the past when Kim Il Sung and Kim Jong-Il were personally involved in discussions. Kim is the only one capable of making big decisions.

And Kim’s apparent willingness not to let the resumption of US-South Korean military exercises, which were delayed for the Olympics, get in the way of talks suggests he is willing to drop his long-standing opposition to the exercises to allow the summit to take place.

So, in principle, this offers an opening for the United States to understand what is possible in moving ahead to mitigate a serious security problem. And President Trump is in a much better position to gain congressional support for any deal he makes than President Clinton was following the 1994 Agreed Framework.

As one analyst has put it, talk of a summit offers an opportunity for “skillful American negotiators to convene an exploratory discussion” with North Korea.

However, it is not at all clear that the Trump administration has the skillful negotiators for this job or is in the mood to undertake a real “exploratory discussion.”

This comes at a time when the US State Department is severely under-staffed, and just a week after the department’s highest level official on North Korea, Joseph Yun, left. Moreover, Trump is likely surrounded by people, as was George W. Bush, who believe the United States should be doing everything it can to see the North Korean government fall, and therefore see negotiations and any US agreement with Kim as undermining that goal. Unless Trump rejects that view, it will be essentially impossible for the administration to develop a workable plan for the summit.

Similarly, even if the summit results in an agreement in principle for North Korea to denuclearize, clarifying what that means to both sides and what steps are necessary and acceptable to reach that point, will be a long and difficult process, and will require detailed negotiations no matter what is decided in principle at high levels. Since the North talks about “denuclearization of the Korean Peninsula,” it is difficult to know exactly what it believes necessary to accompany any reductions in its own arsenal.

US frustrations at those negotiations, or a failure to make progress at the summit itself, could lead to a stronger call in the US for military actions, with people arguing that the diplomatic track has now been tried and failed.

High-level diplomacy is the process of trying to solve the hardest problems. It requires patience, flexibility, innovation, and some amount of holding one’s nose. We have yet to see if the administration is up to this task. That job is complicated by the fact that the US public has been told for many years that you can’t negotiate with North Korea—despite the fact that the US negotiating team in the late 2000 believed they were close to agreements to solve both the nuclear and missile problems. Those negotiations ended when the Bush administration took office in early 2001 and ended the process. Whether North Korea is as serious about negotiations now as they were then remains to be seen.

So, I am happy to see an easing of tensions between the US and North Korea, and am hoping that the Trump administration has understood the limitations of military action and has done more thinking about a diplomatic initiative than it has shown publicly. But I am not particularly optimistic, and remain concerned about the potential pitfalls of this process.

The description of the webinar on the CDC website says: “While a nuclear detonation is unlikely, it would have devastating results and there would be limited time to take critical protection steps. Despite the fear surrounding such an event, planning and preparation can lessen deaths and illness.”

(Source: CTBTO)

On the one hand…

This makes some sense. With global stockpiles of more than 15,000 nuclear weapons in the hands of nine countries around the world, thinking through the consequences of their use is the responsible thing for the CDC to do instead of pretending the world will make it through another few decades without someone detonating a nuclear weapon.

Nuclear use is a particular concern now given the flare-up of tension between North Korea and the United States and the bombastic threats by Kim Jong-un and President Trump (not to mention their recent boasts about their “nuclear buttons”).

Perhaps even more likely is a nuclear war by accident. The United States keeps hundreds of missile-based nuclear warheads on hair-trigger alert with the option of launching them very quickly if early warning sensors report a Russian attack. Russia is believed to do the same. But technical and human mistakes over the past decades have led to a surprising number of cases in which one or the other country thought an attack was underway and started the process to launch a nuclear retaliation. How long until one of those mistakes doesn’t get caught in time?

The use of nuclear weapons could have horrific results. Many US and Russian warheads have explosive yields 20 to 40 times  larger than those of the warheads that destroyed Hiroshima and Nagasaki in 1945.

Because North Korean missiles are not very accurate, it would need to aim its nuclear weapons at large targets, namely big cities. While the United States does not intentionally target cities, many of its warheads are aimed at military or industrial targets that are in or near major population centers. The same is true for Russian targets in the United States.

In addition, a nuclear detonation could have world-wide consequences. Studies have shown that even a relatively limited nuclear exchange between India and Pakistan for example, could eject so much soot into the atmosphere that there would be significant global cooling for a decade. This “limited” nuclear winter could lead to widespread starvation and disease.

So, on the other hand…

A key message of the CDC briefing will hopefully be that the role public health professionals can play following a nuclear attack is relatively small, and the only real option is to prevent the use of nuclear weapons in the first place. This is a case where an ounce of prevention is worth much more than a kiloton of cure.

Given that reality, there are several steps the United States should take to reduce the risk of nuclear use, including:

1. Pursuing diplomacy with North Korea, with the immediate goal of reducing tensions and the risk of military attacks, and a longer term goal of reducing Pyongyang’s nuclear arsenal. Secretary of State Rex Tillerson has made clear repeatedly that he would like to do this. President Trump should get out of his way and let him.
2. Eliminating the option of launching nuclear weapons on warning of an attack and taking all missiles off hair-trigger alert.
3. Changing US policy so that the only purpose of US nuclear weapons is to deter, and if necessary respond to, the use of nuclear weapons by other countries. Under this policy, the United States would pledge to not use nuclear weapons first.
4. Scaling back the $1.2 trillion plan to rebuild the entire US nuclear arsenal over the next 30 years.
5. Starting negotiations on deeper nuclear cuts with Russia and taking steps toward a verifiable agreement among nuclear-armed states to eliminate their nuclear arsenals.

While we are still working through the details, this strongly implies that North Korea could use this missile to carry a nuclear warhead to cities throughout the United States. A final possible barrier people are discussing is whether Pyongyang has been able to develop a reentry vehicle that can successfully carry a warhead through the atmosphere to its target, while protecting the warhead from the very high stresses and heat of reentry.

Here are my general conclusions, which I discuss below:

1. North Korea has not yet demonstrated a working reentry vehicle (RV) on a trajectory that its missiles would fly if used against the United States.
2. However, there doesn’t appear to be a technical barrier to building a working RV, and doing so is not likely to be a significant challenge compared to what North Korea has already accomplished in its missile program.
3. From its lofted tests, North Korea can learn significant information needed for this development, if it is able to collect this information.
4. While the United States put very significant resources into developing sophisticated RVs and heatshields, as well as extensive monitoring equipment to test them, that effort was to develop highly accurate missiles, and is not indicative of the effort required by North Korea to develop an adequate RV to deliver a nuclear weapon to a city.

The Hwasong-15 RV

When the photos appeared after North Korea’s November 29 missile launch, I was particularly interested to see the shape of the front of the missile, which gives information about the reentry vehicle (RV). The RV contains the warhead and protects it on its way to the ground. It appears the Hwasong-15 is carrying an RV that is considerably wider and blunter than that on the Hwasong-14 (Fig. 1).

Fig. 1. The RVs for the Hwasong-14 (left) and Hwasong-15 (right), roughly to scale. (Source: KCNA)

This fact has several implications. A blunter RV can clearly accommodate a larger diameter warhead, and the warhead can sit farther forward toward the nose of the RV. This moves the center of mass forward and makes the RV more stable during reentry. (This drawing shows how the cylindrical nuclear weapon in the US Titan RV, which was roughly the same size and shape, although much heavier, than the Hwasong-15 RV may be.)

A blunter nose on the Hwasong-15 RV also helps protect it from high atmospheric forces and heating during reentry. Here’s why:

As the RV enters the atmosphere, drag due to the air acts as a braking force to slow it down, and that braking force puts stress on the warhead. At the same time, much of the kinetic energy the RV loses as it slows down shows up as heating of the air around the RV. Some of that heat is transferred from the air to the RV, and therefore heats up the warhead. If the stress and/or heating are too great they can damage the RV and the warhead inside it.

A blunter RV has higher drag and slows down in the thin upper parts of the atmosphere more than does a slender RV, which continues at high speed into the thick lower parts of the atmosphere. This results in significantly less intense stress and heating on the blunter RV. In addition to that, a blunt nose creates a broad shock wave in front of the RV that also helps keep the hot air from transferring its heat to the RV.

Fig. 2. This shows two low-drag RVs being placed on a Minuteman III missile, which can carry three RVs. (Source: US Air Force).

A rough estimate shows that if the RVs had the same mass and flew on the same trajectory, the peak atmospheric forces and heating experienced by an RV similar in shape to the Hwasong-14 nosecone in Fig. 1 would be roughly four or more times as great as that experienced by a blunter Hwasong-15 RV; those on a modern US RV, like that on the Minuteman III missile (Fig. 2), might be 20 times as large as on the Hwasong-15 RV.

The tradeoff of having a blunt warhead is that when the RV travels more slowly through the atmosphere it reduces its accuracy. In order to get very high accuracy with its missiles, the United States spent a tremendous amount of effort developing highly sophisticated heatshields that could withstand the heating experienced by a slender, low-drag RV.

For North Korea, the decrease in accuracy due to a blunt RV is not particularly important. The accuracy of its long-range missiles will likely be tens of kilometers. That means that it would not use its missiles to strike small military targets, but would instead strike large targets like cities. For a large target like that, the reduction in accuracy due to a blunt RV is not significant.

What could North Korea learn from its recent test?

Press stories report US officials as saying that the reentry vehicle on North Korea’s November 29 test “had problems” and “likely broke up” during reentry. If true, this implies that the RV used on this flight could not withstand the strong drag forces as the RV reached low altitudes.

It’s worth noting that the drag forces on the RV during reentry on the lofted trajectory would be more than twice as great as they would be on a standard trajectory of 13,000 km range flown by the same missile (Fig. 3). This is because on the flatter trajectory, the RV flies through a longer path of thin air and therefore slows down more gently than on the lofted trajectory. It is therefore possible the RV might survive if flown on a standard trajectory, but North Korea has not yet demonstrated that it would.

However, given the estimated capability of the Hwasong-15 missile, North Korea appears to have the option of strengthening the RV, which would increase its mass somewhat, and still be able to deliver a warhead to long distances.

Fig. 3. This figure shows the atmospheric forces on the RV with altitude as it reenters, for the highly lofted test on November 29 (black curve) compared to the same missile flying a 13,000 km standard  trajectory (a minimum-energy trajectory, MET). The horizontal axis plots the product of the atmospheric density and square of the RV speed along its trajectory, which is proportional to the drag force on the RV. The calculations in all these figures assume a ballistic coefficient of the RV of 100 lb/ft² (5 kN/m²). Increasing the ballistic coefficient will increase the magnitude of the forces and move the peaks to somewhat lower altitudes, but the comparative size of the curves will remain similar.

The situation is similar with heating of the RV. The last three columns of Fig. 4 compare several measures of the heating experienced by the RV on the lofted November 29 test to what would be experienced by the same RV on a 13,000 km-range missile on a standard trajectory (MET).

Fig. 4. A comparison of RV forces and heating on the November 29 test and on a 13,000 km-range trajectory, assuming both missiles have the same RV and payload. A discussion of these quantities is given in the “Details” section below.

These estimates show that the maximum heating experienced on the lofted trajectory would be about twice that on a standard trajectory, but that total heat absorbed by the RV on the two trajectories would be roughly the same. Because the heating occurs earlier on the RV on the standard trajectory than on the lofted trajectory, that heat has about 130 seconds to diffuse through the insulation of the RV to the warhead, while the heat on the lofted trajectory diffuses for about 80 seconds (Fig. 5). This somewhat longer time for “heat soak” can increase the amount of heat reaching the warhead, but North Korea would put insulation around the warhead inside the RV, and the heat transfer through insulators that North Korea should have access to is low enough that this time difference is probably not significant.

Fig. 5: This figure shows how the heating rate of the RV surface varies with time before impact on the lofted and standard trajectory. The areas under the curves are proportional to the total heat absorbed by the RV, and is only about 20% larger for the MET. The vertical axis plots the product of the atmospheric density and the cube of the RV speed along its trajectory, which is proportional to the heating rate on the RV.

Fig. 6 shows heating on the two trajectories with altitude.

Fig. 6. This figure shows the heating of the RV with altitude as it reenters.

These results show that if North Korea were able to demonstrate that its RV could survive the peak drag forces and heating on a lofted trajectory, it should also be able to survive those on a standard trajectory. As noted above, the estimated capability of the Hwasong-15 missile suggests North Korea would be able to increase the structural strength of the RV and its heat shielding and still be able to deliver a warhead to long distances.

There is still some question about what information North Korea may actually be getting from its tests. One advantage of testing on highly lofted trajectories that fall in the Sea of Japan is that the RV can presumably radio back data to antennae in North Korea for most of the flight. However, because of the curvature of the Earth, an antenna on the ground in North Korea would not be able to receive signals once the RV dropped below about 80 km altitude at a distance of 1000 km. To be able to track the missile down to low altitudes it would likely need a boat or plane in the vicinity of the reentry point.

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 through the atmosphere. 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. Similarly, forces due to atmospheric drag are proportional to ρV², and also increase rapidly with missile range.

The calculations above assume a ballistic coefficient of the RV equal to 100 lb/ft² (5 kN/m²). The ballistic coefficient β = W/C_dA (where W is the weight of the RV, C_d is its drag coefficient, and A is its cross-sectional area perpendicular to the air flow) is the combination of parameters that determines how atmospheric drag reduces the RV’s speed during reentry. The drag and heating values in the tables 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.

Based on the shape of the front of the Hwasong-15, I estimate that the drag coefficient C_d of its RV is 0.35-0.4. That value gives β in the range of 100-150 lb/ft² (5-7 kN/m²) for an RV mass of 500-750 kg. The drag coefficient of an RV similar in shape to the front of the Hwasong-14 is about 0.15.

Updated 12/8/17.

But the details suggest the crew instead saw the missile early in flight, and probably did not see an explosion.

One report of the sighting by the Cathay CX893 crew gives the time as about 2:18 am Hong Kong time, which is 3:18 am Japan time (18:18 UTC). According to the Pentagon, the launch occurred at 3:17 am Japanese time (18:17 UTC), which would put the Cathay sighting shortly after the launch of the missile from a location near Pyongyang, North Korea.

Since the missile flew for more than 50 minutes, it would not have reentered until after 4 am Japanese time. Given the timing, it seems likely the crew might have seen the first stage burn out and separate from the rest of the missile. This would have happened a few minutes after launch, so is roughly consistent with the 3:18 time.

The New York Times posted a map that shows the track of flight CX893. It shows that the flight was over northern Japan at 6:18 pm UTC (Fig. 1) and the pilots would have had a good view of the launch. By the time reentry occurred around 7:11 pm UTC, the plane would have been over mid-Japan and reentry would have occurred somewhat behind them (Fig. 1).

Fig. 1. Maps showing the location of flight CX893 shortly after launch of North Korea’s missile near the red dot on the left map, and at the time of reentry of North Korea’s missile, which took place near the red dot on the right map. (Source: NYT with UCS addition)

Burnout of the first stage would have taken place at an altitude about 100 km higher than the plane, but at a lateral distance of some 1,600 km from the plane. As a result, it would have only been about 4 degrees above horizontal to their view—so it would not have appeared particularly high to them. Ignition of the second stage rocket engine and separation of the first stage may have looked like an explosion that caused the missile to fall apart.

There are also reports of two Korean pilots apparently seeing a “flash” about an hour after the missile’s launch, which would be consistent with the warhead heating up during reentry, since the missile flew for 53-54 minutes. Neither reported seeing an explosion, according to the stories.

Reports are saying that the missile test was highly lofted and landed in the Sea of Japan some 960 km (600 miles) from the launch site. They are also saying the missile reached a maximum altitude of 4,500 km. This would mean that it flew for about 54 minutes, which is consistent with reports from Japan.

If these numbers are correct, then if flown on a standard trajectory rather than this lofted trajectory, this missile would have a range of more than 13,000 kilometers (km) (8,100 miles). This is significantly longer than North Korea’s previous long range tests, which flew on lofted trajectories for 37 minutes (July 4) and 47 minutes (July 28). Such a missile would have more than enough range to reach Washington, D.C., and in fact any part of the continental United States.

We do not know how heavy a payload this missile carried, but given the increase in range it seems likely that it carried a very light mock warhead. If true, that means it would be incapable of carrying a nuclear warhead to this long distance, since such a warhead would be much heavier.

(Source: US State Dept.)

Since the agreement includes several other countries, that would significantly weaken the deal but would not end it.

Still, that the United States would undermine the agreement—which administration officials acknowledge Iran is abiding by—is incredibly short-sighted. It goes against the advice of President Trump’s senior advisors and essentially the whole US security policy community. It erodes US credibility as a treaty partner in future negotiations.

Killing the deal would throw out meaningful, verified limits on Iran’s ability to make nuclear weapons because the president doesn’t think the agreement goes far enough.

The US did this with North Korea, and it was a disaster

The US did this before—with North Korea—and that led to the crisis we are in today.

In 2001, when the Bush administration took office, there was an agreement in place (the Agreed Framework) that verifiably stopped North Korea’s production of plutonium for weapons and put international inspectors on the ground to make sure it was not cheating. This stopped Pyongyang from making fissile material that could be used for dozens of nuclear weapons, and provided the world valuable information about an intensely opaque country.

Also by 2001 North Korea had agreed to stop ballistic missile tests—which was readily verified by US satellites—as long as negotiations continued. This was also meaningful since it would cap Pyongyang’s missile capability at a range of only 800 miles.

Former Secretary of Defense William Perry, who was closely involved in the negotiations with Pyongyang, has said he believes at that point the United States was a couple months from reaching an agreement that would have ended the North’s nuclear and missile programs. This was years before North Korea had done any nuclear tests or long-range missile tests.

Instead of capturing these important restrictions and building on them, the Bush administration—like Trump today—argued these limits were flawed because they did not go far enough to reign in the whole range of activities the United States was concerned about. Bush stopped the talks and eventually let the constraints on North Korea’s nuclear and missile programs fall apart, bringing us to where we are today: facing a North Korea with hydrogen bombs and long-range missiles.

One reason the Bush administration gave for stopping implementation of the Agreed Framework was that Pyongyang had a fledgling uranium enrichment program that was not captured by the agreement. US negotiators knew about that program in the 1990s, and were watching it, but decided that ending Korea’s operating plutonium-production capabilities and getting inspectors on the ground was the crucial first step, and with that in place the uranium program could be addressed as a next step. The Agreed Framework was not meant to be all-encompassing—it was an important, logical step toward solving the bigger problem that was too complex to be solved all at once.

The Iran deal was similarly seen by those negotiating it as a meaningful, achievable step toward solving the bigger issues that could not be addressed all at once. And it has been successful at doing that.

Drifting toward disaster

In the case of Iran, as well as North Korea, President Trump is taking provocative steps that go against the advice of his senior advisors—and in many cases simply defy common sense. The stakes are extremely high in both cases. Dealing with them requires an understanding of the issues and potential consequences, and a long-term strategy built on realistic steps and not magical thinking.

If Trump de-certifies the Iran agreement, he will be tossing the fate of the deal to Congress. Congress needs to heed the advice the president is not taking. That means it should listen to Secretary of Defense James Mattis; Gen. Joseph Dunford, chair of the Joint Chiefs of Staff; Secretary of State Rex Tillerson; and others who believe it is in the best interests of the United States to continue to support the agreement.

We find ourselves in a situation in which the whims of the president are escalating conflicts that potentially put millions of lives at risk and create long-term security risks for the United States, and no one appears to have the ability to reign him in and stabilize things. That situation should be unacceptable to Congress and the US public. If this situation continues, it could go down as one of the darkest periods of US history.

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.

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.

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.

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.

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.

South Korean sources reported this test had a range of 500 kilometers (km) (300 miles) and reached an 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 were 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 they are moved to a launch site. By contrast, large liquid-fuel  missiles must be without fuel and then fueled after they are in place at the launch site. This process can take an hour or so, and the truck carrying the missile must be accompanied by a number of trucks containing fuel. So it is easier to detect a liquid missile before launch and there is more time  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 from there. North Korea 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, such as France and China, it took them several decades to get from the point of building a medium-range solid missile, which North Korea has done, 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.