Using “rocket science” to understand North Korea’s space and missile efforts
by James Oberg
|It is very likely that the satellite failure in December was due to inadequate robustness of the satellite’s systems, and that same weakness would be expected to be found in warheads.|
And far from proving the peacefulness of the launch, the trip showed that North Korea refused to provide any crucial insight into the degree of weaponization of the rocket. They showed us everything but the important things, the features that could have clearly demonstrated peaceful intent of that particular launching.
Following that visit, NBC news was briefed by US military intelligence specialists on their estimates for North Korean nuclear weapons. As reported in an article on the NBC website:
At the high end of the range, U.S. officials and other researchers said, North Korea may already have up to “a few dozen” nuclear weapons that could be fitted atop its vast fleet of ballistic missiles. Currently, North Korean missiles are limited to an intermediate range, capable of hitting cities in Japan or South Korea but not the United States. What the new test could reveal is an improvement in the type of weapons North Korea has.
And following the successful orbital launch in December of what was claimed to be an Earth observation satellite, North Korea again failed the “openness test” by concealing what the rest of the world soon realized: the satellite was dead-on-arrival in orbit, a drifting derelict.
As North Korea recapitulates the “missile race” of the US and USSR in the late 1950s, two particular crucial steps now stand out as yet to be demonstrated. Recent events, seen against historical patterns, seem to show the following:
First, the heat shielding for a reentry vehicle carrying a warhead remains a serious technological challenge. North Korea is probably capable of developing an “ablative” shield—one that absorbs the tremendous heat of atmospheric reentry by spalling layers away—on its own, or with materials obtained elsewhere in the world. And testing of such equipment may have already started.
Second, the ruggedness of rocket-borne equipment is also a challenge, considering the accelerations, vibration, and acoustic levels of ascent into space. It is very likely that the satellite failure in December was due to inadequate robustness of the satellite’s systems, and that same weakness would be expected to be found in warheads.
These were some of the major challenges of the original missile race, more than half a century ago. And one lesson we saw on our April visit to the launch site and satellite control center is that the North Koreans prided themselves on working things out for themselves. They seemed almost to boast about how they didn’t need to learn from any other country’s experiences.
If that really was their attitude, they were setting themselves up for suffering a string of avoidable mistakes. And that may be good news for the rest of the world, but it can’t last.
The December launching succeeded, for the first time, quite possibly as a consequence of a more realistic management approach to caution. As the launch date approached, press reports told of how the rocket team had vowed to increase the quality and care of their own work.
|Pyongyang has yet to admit this embarrassing failure, despite pre-launch promises the satellite would be sending back streams of photographs of North Korea for use in land management and disaster relief.|
This was a major step forward in accepting responsibility for the failure and not blaming foreign enemies for sabotage. It was also a repudiation of the enthusiastic blind faith expressed by our hosts in April. Two of the three main briefers we met, including the director of the launch site, disappeared after that failure, their names left off the “honors list” for the December launch success.
But as NBC News first revealed, the new satellite was delivered into space already dead. Subsequent observations around the world confirmed that it never functioned, never emitted a single “beep,” and remains slowly tumbling end over end, a derelict from the moment it reached orbit.
Pyongyang has yet to admit this embarrassing failure, despite pre-launch promises the satellite would be sending back streams of photographs of North Korea for use in land management and disaster relief (and post-launch staged media events in the control center where patriotic music allegedly “beamed from the satellite” was broadcast over speakers.) A Turkish satellite, home-built for the same purpose but launched in December on a Chinese rocket, and a South Korean satellite of similar purpose launched earlier this year with a first-stage rocket bought from Russia, have already been sending such pictures. But not one snapshot has been released from the North Korean bird. From Pyongyang there is nothing but silence, and blank screens.
Since one can presume that the satellite was properly functioning in the pre-launch checkout, it is reasonable to postulate a cause-and-effect process of its subsequent failure as a direct result of the launching. High acceleration forces, severe acoustic and vibrational forces, and even post-insertion collision with the third stage are all well-known potential causes of payload failure. They have killed a number of satellites in other national programs over the years.
This satellite failure is more than merely embarrassing, or inconvenient for propaganda. It has direct bearing on the construction of a reliable nuclear warhead for a long-range missile, the same type of rocket that launched—and in so doing evidently broke—the satellite. True, a warhead and a satellite are different devices, of course, but they share critical control components, mostly electronics, but also rocket steering thrusters. In North Korea they probably come out of closely-related workshops.
Recovery from this setback could be time-consuming. North Korean plans involve launching two more “earth observation” satellites, but with no telemetry from the last satellite, diagnosing exactly what went wrong could take a long time. In the meantime, the efficacy of many of the key components for long-range warheads must also now be called into question.
Meanwhile, testing of warhead heat shielding is also necessary. Ground laboratories can simulate some of the heat flow, but flight tests with actual deceleration stresses are also required.
Popularly, the reentry heating is called “frictional” heating, as generated by air streaming hypersonically across the outer skin of a falling vehicle. The term came into use during the higher/faster rocket plane missions of the streamlined ‘X’ series in the 1950s and 1960s.
But technically speaking, warhead heating is mostly caused by a different process. Since warheads may not be streamlined, but often are blunt shapes, the air piles up in front of a falling warhead like snow in front of a speeding snowplow. The air is forcefully compressed, creating heat like the heating in a bicycle pump when filling a tire, and that hot air flows across the warhead, heating it in turn. The speed of the air across the warhead (or even the skin of a space shuttle) is subsonic, so classical “frictional” heating is not the main cause.
It doesn’t matter. Everybody still calls it frictional heating, out of old habits, so it’s not worth making a big issue over the term. Modern US warheads tend to be cone shaped for fast penetration and friction really is the key heating cause. But understanding the real difference is crucial to correctly designing a basic protective system within reach of North Korea.
|A rocket to test warhead heat shields is virtually identical to a rocket for launching small satellites, since the desired speeds are similar.|
Historically, even the German short-range V-2 missiles of World War II experienced enough heating to detonate their explosives. This required adding layers of plywood as makeshift heat shielding. By the time long-range missiles appeared in the mid-1950s, the designers had run into the wall of severe heating. The Soviet Union’s much-vaunted intercontinental ballistic missile test of August 1957 frightened the US, but the CIA didn’t learn for years that the first test warheads in those launchings burned up during reentry, stalling the program until effective shielding could be fabricated.
Wernher von Braun’s team in the US designed a special test vehicle for verifying heat-shielding technology in 1956-7, called the Jupiter-C. It succeeded in pushing a test warhead back into the atmosphere at speeds equivalent to long-range flights. With a minor modification the Jupiter-C (renamed Juno-1) soon afterward launched the first American earth satellite, Explorer 1. This underscores a contemporary issue: a rocket to test warhead heat shields is virtually identical to a rocket for launching small satellites, since the desired speeds are similar.
North Korea could conduct such test flights at any time, either as overt missile tests or disguised as satellite launchings. And as we saw last April, they may already have done so.
For the heat shield test, the rocket does not have to fly across the Earth’s surface to its full range and thus be visible to watching eyes along the entire track. It could pop up into space and then, its second and then third stages still firing, turn back down into the atmosphere to attain the speeds equivalent to a full-range firing.
In that profile, outside observers would only see a much shorter flight. It might be harder to determine what was actually being tested. Seeing recovery ships in an impact zone only 1000 kilometers off the North Korean coast might be one clue, but the test warhead may only have to relay a brief radio burst confirming its survival before splashing into the ocean and sinking out of sight.
Alternately, a supposedly “peaceful” launch could have a secret secondary payload. Warhead heat shield tests could piggyback on genuine satellite launchings. They could have a test profile designed to use normal first and second stage booster jettisons as camouflage for the presence of the test warhead.
The scary thing is, that might already have been done, on the launches last year. Despite repeated promises, our hosts never showed us what was under the rocket’s shroud. We never even saw video or still photos of the satellite we had previously been shown actually being installed on the rocket. So we never were given proof that such a hidden test had not been carried out.
We were repeatedly given a series of arguments of how the Unha-3 rocket we saw, and were supposed to watch being launched, was entirely peaceful. We were told that the liquid propellants proved its peacefulness, since other countries used only solid propellants for long-range military missiles. But that was false: both Russia and China have liquid-fueled ICBMs, and the Unha-3 was based on a Soviet-era design of a military missile.
We were told that the massive launch tower showed that these missiles would always be easily seen by outside observers. But that was silly: if a few such missiles were deployed as weapons, they would likely be built into bays in civilian urban apartments, easy to camouflage. All the rocket hardware was road mobile—no rail transport or long-distance fuel pipelines were needed—so they could be deployed anywhere.
|The most striking memory I have of that day, the rocket’s failure day, was the astonishment of the North Korean officials sitting in the press room.|
We were shown the satellite that was supposed to be loaded onto the rocket, but we were never shown any evidence that the satellite actually was loaded, or that other objects were not loaded with it. Explicit promises were made, in contentious discussions, to provide such evidence, and all the promises were broken.
Lastly, we were promised that we would “observe the launching”, a degree of transparency which Pyongyang spokesmen explicitly described as proving the peaceful nature of the rocket’s flight. So we were expecting to watch a televised live broadcast, perhaps with a few minutes advance warning so we could gather in the conference center at the hotel.
We were never alerted to the launch,when it actually occurred. And in an even more bizarre repudiation of the intended demonstration of peacefulness, once the rocket was launched—and quickly failed—our hosts never acknowledged it had happened. They not only never explained it, they never even remembered why we had come to Pyongyang in the first place. Instead, we were bussed off to a statue unveiling attended by Kim Jong Un.
The most striking memory I have of that day, the rocket’s failure day, was the astonishment of the North Korean officials sitting in the press room. They clearly were caught without any contingency plans for failure—they had no cover story—and in the face of confrontational badgering from visiting journalists, they sat staring blankly at the opposite wall like Buckingham Palace guards. In a moment when the journalists clustered around a laptop displaying hot rocket news from overseas, they slipped away unseen, never to appear again.
But hiding is not an effective strategy in the space business, and we saw plenty—then and later—to help figure out things we weren’t supposed to know. Sleuthing space secrets didn’t become an obsolete art with the collapse of the Soviet Union, as a lot of us had feared it might.