By Michael Elleman
10 February 2016
On February 7, 2016, North Korea boosted a small satellite into space from the Sohae Satellite Launching Station using a three-stage, liquid-fueled Unha rocket. According to a CBS News report, the Kwangmyongsong-4 satellite is orbiting earth, but is tumbling and likely inoperative. The controversial launch violates numerous United Nations Security Council resolutions, which proscribe North Korea from using ballistic missile technologies, including satellite launches. Historically, North Korea has paired its rocket launches with nuclear detonations a few weeks later, though in this case, the order of events was reversed.
While all North Korean rocket tests should be discouraged and condemned, the magnitude of punitive sanctions applied to the already heavily isolated regime should be consistent with the threat posed by the type of rocket launched. Long-range ballistic-missile flight tests are far more menacing than a satellite launch using a rocket designed for space missions. American efforts to deter and prevent North Korea from flight testing the KN-08, Musudan or other long-range ballistic missile must take priority over unwelcomed satellite launches using the Unha or equivalent rockets.
North Korea has fired five long-range rockets since 1998. The first test in August 1998 involved the Taepodong-1, a three-stage rocket launched from the Musudan-ri site on the eastern shores of the peninsula. The first two stages performed as designed, and the third stage separated from the second, but malfunctioned soon thereafter. The third stage and the satellite plunged into the Pacific Ocean roughly 1,600 km from the launch site.
Eight years after the Taepodong-1 firing, North Korea launched a much larger rocket in July 2006. The Taepodong-2, as it was named by US intelligence, exploded just 42 seconds into its flight. There were no photographs or videos of the launch.
On April 5, 2009, North Korea attempted to boost a small satellite into orbit using a three-stage, Unha-2 rocket from Musudan-ri. Flight data collected and released by the Japanese Defense Forces indicate that the first two stages performed as intended. The failure of the third stage to separate from the second—or a third-stage ignition malfunction—doomed the flight, leaving the third stage and satellite to tumble out of control and fall into the ocean roughly 3,200 km from the launch site. Photographs and video of the launch broadcast by North Korea’s state-owned television offered a first public glimpse of the rocket’s size and approximate configuration.
Three years later, a slightly modified version of the Unha-2, named Unha-3, was assembled, prepared and then launched from the new Sohae site on April 12, 2012. As the rocket lifted off toward the south as expected, it reportedly failed approximately 100 seconds into first stage operation. The precise nature of the failure is unknown, though remnants of the first stage were recovered by South Korea. Analysis of the debris confirmed that the first stage consists of a cluster of four Nodong engines, each operating independently, and four small vernier engines to steer the rocket.
In November 2012, Pyongyang declared that it would attempt for a second time to boost the Kwangmyongsong-3 satellite into a sun-synchronous orbit. Assembly, systems checks and fueling of the Unha-3 at the Sohae facility continued for about two weeks. Poor weather and minor technical glitches delayed the launch a few additional days. On December 12 that year, the Unha-3 successfully inserted a satellite into orbit, though the satellite failed to stabilize and orient itself relative to the earth’s surface, precluding it from capturing images of the earth’s surface as designed.
The most recent launch is very nearly a repeat of the December 2012 firing, although the Kwangmyongsong-4 satellite is reported to weigh 200 kg, about twice as much as the previous one. This may help explain why the designated splash down zones for the first and second stages were slightly less than for the 2012 firing, though other possibilities may have contributed to the change as well.
The Kwangmyongsong-4’s orbital parameters (501 x 466 km, at 97.5 degrees) differ from the sun-synchronous orbit North Korea forecasted, suggesting that the Unha rocket experienced a small aiming deviation. Further, the US announced that the satellite was tumbling in its orbit, another sign that the mechanism that frees the satellite from the third stage did not perform as expected. Nevertheless, North Korea succeeded for the second time in placing an object into orbit.
Satellite Launch or Ballistic Missile Test?
Satellite launches, especially those lifting payloads to low-earth orbits, initially boost upwards, but then accelerate the payload on a path nearly parallel with the earth’s surface to reach the velocity needed to sustain the orbit. Low-thrust engines are typically used during the latter phase of the boosted trajectory to achieve the needed radial velocity. The maximum altitude of the payload is on the order of 200 to 500 km, depending on the orbital parameters required by the mission. Ballistic missiles, on the other hand, boost the warhead to high altitudes, allowing the payload to coast downrange to a maximum distance. A 10,000 km range intercontinental ballistic missile (ICBM) reaches a peak altitude of more than 1,000 km when on a minimum energy (i.e. maximum range) trajectory. Lifting a warhead to such heights requires high-thrust engines to avoid gravity losses while accelerating upward.
With the exception of the July 2006 firing of the Taepodong-2, which exploded too early in its liftoff trajectory to determine its mission, all of the other large rockets launched by North Korea were designed to maximize performance as a satellite launcher. In each case, the Taepodong-1 and Unha rockets flew on trajectories fully consistent with a satellite launch. Further, the Taepodong-1 used a low-thrust (Isayev 5D67) engine scavenged from an S-200 (NATO designated SA-5) air-defense missile on the second stage. Flight data displayed in the North Korean control room during the December 2012 Unha-3 launch, indicate that the second stage is a modified Scud-B missile with a larger diameter airframe to hold more fuel. The third stage is likely similar to that found on Iran’s Safir carrier rocket, which consists of vernier (i.e. steering) engines from either the Soviet R-27 (NATO designated SS-N-6) submarine-launched ballistic missile (SLBM), or another Soviet system, such as the ROTA, which was never fielded by the Soviet Union. The Unha’s use of long-burning, low-thrust upper stages is optimal for space missions, though if used as a ballistic missile, the low-thrust engines would suffer significant gravity losses during its upward trajectory, robbing the missile of roughly 800 km of range.
Can a Satellite Launch Vehicle be Used or Converted into an ICBM?
Without question, rockets designed to boost a satellite into orbit and long-range ballistic missiles employ many of the same technologies, key components and operational features. There are, however, key characteristics that differentiate satellite launchers from ballistic missiles, apart from the payload itself. Firstly, ballistic missile payloads must survive the rigors of re-entry into the earth’s atmosphere. Protecting a long-range missile’s payload from the extreme heat and structural loads experienced during re-entry requires the development and production of special materials, as well as testing and validation under real conditions.
Secondly, as discussed previously, satellite launch vehicles and long-range ballistic missiles employ distinctly different trajectories to fulfil their respective missions. The different trajectories call for different propulsion systems for optimal performance. One cannot simply swap out one engine for another and expect the missile to perform with high dependability. Multiple flight tests of the new configuration are needed to validate performance and reliability.
A third, less obvious difference lies with the operational requirements. Before flight, satellite launchers, unlike their ballistic missile counterparts, are prepared over a period of many days, if not weeks. Components and subsystems are checked and verified prior to launch, and the mission commander has the flexibility to wait for ideal weather before initiating the countdown. If an anomaly emerges during the countdown, engineers can delay the launch, identify and fix the problem, and restart the process. Recall that the Unha rockets launched to date have required at least a week, if not a full month to assemble and prepare for launch.
In contrast, ballistic missiles, like other military systems, must perform reliably under a variety of operational conditions, with little or no warning. These operational requirements impose a more rigorous validation scheme, which includes an extensive flight-test program. Normally, only after successfully completing validation testing is a missile deemed to be combat ready. This latter requirement and the need to ensure pre-launch survivability explain why the Soviets and Americans never converted a satellite launcher into a ballistic missile, though the reverse process occurred frequently. China developed its early long-range missiles (DF-3, DF-4, and DF-5) and satellite launchers (CZ-2 and CZ-3) in parallel. However, running the developmental programs in tandem did not obviate the need to conduct a full set of flight trials over many years for the military missiles. Nor did the parallel programs shorten the development timeline significantly.
North Korea could certainly opt to modify the Unha satellite launch platform for use as a ballistic missile, though the transformation would not be simple or quick. There would still be a need to flight test the transformed Unha in a ballistic missile mode. If North Korea built a ballistic missile using the first two stages of an Unha-3, the notional missile might achieve a maximum range of 4,000 to 6,000 km, depending on configuration details. To reach the continental US, a powerful third stage would have to be developed and added to the first two stages of the Unha-3. The notional missile would remain poorly suited for use as a ballistic missile, however, especially if the low-thrust Scud engine was retained by the second stage.
The Soviet Union considered an analogous upgrade in 1957, when the Yangel Design Bureau suggested combining the main boosters of the R-12 and R-14 missiles to create the R-16 ICBM. The R-16 was successfully developed, but only after substantial redesign, including the development of new engines using more energetic propellants. The Soviet experience suggests that North Korea might find it challenging and time consuming to build an operational ICBM derived mainly from Unha-3 hardware.
North Korea could contemplate using the Unha-3 as the basis for an ICBM for emergency use in the direst of circumstances. The missile would weigh more than 90 tons, making it too large and cumbersome to be viably deployed on a mobile launch platform. Silo deployment might be possible, but North Korea is a relatively small country, with limited strategic depth, and would find it difficult to conceal the location of its silos. All of North Korea’s silos would be fewer than 200 km from the coastline and thus vulnerable to pre-emptive strikes by advanced military powers, such as the US, or boost-phase intercept using SM-3 interceptors deployed on Aegis ships patrolling near the Korean peninsula.
For an ICBM, a new missile design seems more likely. In April 2012, North Korea unveiled mock-ups of a mobile, long-range missile, dubbed Hwaseong-13 or, in US nomenclature, KN-08, during a military parade in Pyongyang. The missile has never been tested, and its origins and hardware configuration are not known. The configuration of the KN-08 has also undergone modifications, as suggested by the most recent display of the missile during a military parade in Pyongyang. If propellants more energetic than those used by the Unha-3, Nodong or Scud missiles were employed, the new missile might be capable of intercontinental range. But until it is flight tested, such possibilities remain speculative.
There are reports that North Korea has already deployed the KN-08, as well as the Musudan. Because neither of these missiles have been flight tested, Pyongyang would necessarily have to assume great risk of failure should it attempt to fire them in anger. A cursory review of first- and second-generation development of long-range ballistic missiles—and satellite launchers—in the US, Soviet Union, China and France show that a new missile is more likely to fail than succeed over the first half-dozen flights. North Korea’s Unha rocket failed three times before succeeding. While an untested ballistic missile could be fired during a crisis that threatens directly the Kim Jong Un regime, it cannot be viewed as a reliable strategic capability.
How Should the US Respond?
North Korea has now successfully boosted two objects into orbit using variations of the Unha rocket. This achievement comes after three failed attempts using an Unha rocket, and one failed Taepodong-1 rocket. The results suggest that North Korean engineers have learned how to design, assemble and operate a multi-stage rocket, record enough flight data to identify and fix malfunctioning subsystems or processes, and systematically improve a newly developed system’s performance and dependability. Future satellite launches using Nodong and Scud technologies will likely enhance the reliability of the Unha rocket, and facilitate the development of a larger version of the Unha, perhaps the Unha-9. The accumulated experience and knowledge of past and future satellite launches will not significantly contribute to the design and development of a viable and reliable long-range ballistic missile. As history has demonstrated, satellite launch activity does not provide a shortcut. If North Korea wants to have a credible nuclear capability, one that threatens the United States directly, it will necessarily have to commit to an extensive flight-test program involving the KN-08 and Musudan ballistic missiles.
Having never flight tested the Musudan and KN-08, Pyongyang has no measure of their respective performance and dependability. Threatening to use or firing the untested missiles would be risky adventure. First- and second-generation, long-range ballistic missiles developed by the US, Soviets, Chinese and French failed their first ten flight tests more often than they succeeded. The Unha failed on its first three firings. Thus, Pyongyang would have to assume great risk of failure if it threatened to launch or fired the KN-08, Musudan or other long-range missile before it validated its reliability. It is therefore highly unlikely that Pyongyang would elect to fire its unproven missiles except under the direst of circumstances, such as the regime coming under direct military threat by a foreign army.
Stopping North Korea from flight testing either or both of these missiles, or similar long-range systems, must be a strategic priority for the Washington, second only to preventing Pyongyang from transferring nuclear material or technology, and detonating additional nuclear bombs. If North Korea succeeds in developing the KN-08, or equivalent, it could threaten the US mainland and erode America’s long-standing extended deterrence commitments to South Korea, Japan and other regional allies. Deterring future satellite launches is important, but not at the cost of preventing long-range missile tests.