Seoul’s missile activities have long been constrained by decades-old limits that South Korea agreed on with its longtime ally, the United States. At various junctures, these limits have gradually been loosened, though the latest such change may not upset the regional security balance as much as it may appear to at first blush.

Most recently, following nine months of negotiations, the United States and South Korea agreed to further revise these bilateral missile guidelines in the summer of 2020. On July 28, 2020, South Korean Deputy National Security Adviser Kim Hyun-chong announced that, pursuant to the newly agreed revisions, South Korean individuals and entities will be, for the first time, capable of “developing, producing, and possessing” space launch vehicles (SLVs) making use of solid rocket motors without restrictions. Kim went on to announce, “As of July 28, 2020, limits on the use of solid fuel in space launch vehicles are completely removed.”

The decision opens a new era for South Korean space launch activities and has raised questions about possible military applications for large-diameter solid rocket boosters. While these technologies hold economic promise for a country that seeks to scale its space program quickly, they can also contribute to a long-range missile program. Ballistic missiles that use solid propellants are generally more operationally nimble than their liquid-propellant counterparts and, as a result, can be more militarily useful.

Ankit Panda
Ankit Panda is the Stanton Senior Fellow in the Nuclear Policy Program at the Carnegie Endowment for International Peace.
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The revised guidelines were announced during the start of a new era of possible missile proliferation in the Asia-Pacific region, and these revisions coincide with a deteriorating geopolitical environment amid growing U.S.-China frictions. Moscow’s and Washington’s scrapping of the 1987 Intermediate-Range Nuclear Forces Treaty in 2019 has introduced the possibility of new U.S. short- and intermediate-range conventional missile deployments in Asia.[1] Meanwhile, Japan and Australia are both exploring standoff strike capabilities to better deter perceived threats, China continues to expand its large arsenal of conventional and dual-capable missiles, and North Korea keeps on qualitatively refining and quantitatively expanding its missile capabilities. The revised U.S.–South Korea guidelines have sparked some concerns that Seoul may harbor other motives beyond facilitating civilian spacefaring activities and that this revision may ultimately set up Seoul for a longer-range, more capable missile arsenal.

But a closer look at South Korea’s objectives suggests the July 2020 guideline revisions are not what should really draw attention. Instead, Seoul’s indigenous ballistic missile programs, which have continued apace under gradually slackening bilateral guidelines over the years, should be the primary focus. South Korea’s Agency for Defense Development (ADD) is already pursuing capabilities, within the confines of a prior revision to the guidelines, that open up new missile possibilities for Seoul and that may heighten the odds of misperceptions in the region.

Earlier Revisions to the Guidelines

The U.S.–South Korea missile guidelines have been revised before. The July 2020 decision represents the third significant revision to the forty-one-year-old guidelines—originally agreed upon in a classified 1979 bilateral understanding—in the last decade. In 2012, a previous conservative South Korean government, led by then president Lee Myung-bak, clinched an agreement allowing Seoul to develop ballistic missiles capable of delivering 500-kilogram payloads to ranges of up to 800 kilometers (sufficient to strike all of North Korea from Daegu, a southern city in South Korea). Seoul had requested the range extension to augment its autonomous strike capabilities following twin provocations in 2010: a North Korean torpedo sunk a South Korean corvette, ROKS Cheonan, and North Korean artillery shelled the South Korean–controlled Yeonpyeong Island.

The 2012 revision followed a 2001 extension of the original 180-kilometer range limit to 300 kilometers. This earlier revision was linked to Seoul’s accession to the Missile Technology Control Regime (MTCR), a cartel of states capable of producing technologies necessary for manufacturing advanced ballistic missiles; at that time, this revised limit matched the regime’s Category I range and payload limits.

Fast-forwarding to the near present, in 2017, the administration of U.S. President Donald Trump, amid breakneck North Korean qualitative advances in missile technology, reached an agreement with South Korean President Moon Jae-in’s administration to eliminate the payload weight limit entirely while maintaining the 800-kilometer missile range restriction. Yet none of these revisions had affected South Korea’s space launch technologies—until the July 2020 announcement.

South Korean Solid Propellants

Until now, South Korean indigenous SLVs have relied on liquid-bipropellant combinations that would be poorly suited for anything but orbital launches. For instance, the Korea Aerospace Research Institute’s (KARI) Nuri, also known as Korea Satellite Launch Vehicle-II (KSLV-II), employs liquid oxygen (LOX) and a kerosene variant as its oxidizer-fuel combination across all three missile stages. Cryogenic liquid oxidizers, like LOX, have several advantages, but major operational drawbacks in terms of their handling and storage have kept them from being used in modern ballistic missiles. First-generation U.S. and Soviet intercontinental ballistic missiles (ICBMs)—like the Atlas and the R-7, for instance—employed LOX, but their successors quickly moved to noncryogenic hypergolic liquid bipropellants before eventually settling on solid propellants.

Solid propellants for long-range, large-diameter rockets have a similar appeal when used for orbital and suborbital applications whether they are employed for civilian or military purposes. With the fuel cast directly into their airframes, solid rocket motors can be readied for use with considerably less pre-launch preparation, assuming proper handling and storage. (Proper storage and transportation of solid rocket motors are nontrivial considerations.) This characteristic makes solid propellants often preferable for military applications—especially for small-diameter missiles.

Solid fuels do have their drawbacks, however. For instance—unlike liquid-propellant engines, which can be remotely shut off—once ignited, solid-fuel engines will burn until all available fuel is consumed. Seoul’s presented rationale for pursuing solid-propellant SLVs does not rule out the possibility that new solid boosters may eventually be used as ballistic missiles, but the main focus for now is on enabling cheaper surveillance satellite launches.

Kim, South Korea’s deputy national security adviser, was quite open in his July press conference that Seoul envisages potentially using new, solid-propellant orbital launchers to send observation satellites into low-Earth orbit. “Theoretically, we can launch a low-Earth orbit satellite via liquid-fuel rockets, but it’s like delivering a dish of jjajangmyeon [a Korean noodle dish] by [way of] a 10-ton truck,” he added, apparently seeking to make the case for the economical nature of delivering smaller payloads in this manner.

This point bears emphasizing: it can be more economical for a space program to scale around solid rocket boosters, depending on the types of payloads and desired orbits. As South Korea looks to improve its indigenous intelligence, surveillance, and reconnaissance (ISR) capabilities against North Korea in the coming years, military surveillance satellites will come to play a more important role in South Korean military planning.

Such capabilities are also an important barometer for facilitating larger alliance goals, namely the transfer of wartime operational control (OPCON) from the U.S. military to South Korea’s own forces. The South Korean forces under the alliance’s Combined Forces Command have been led by U.S. military generals for some time, but Seoul has long aspired to regain the operational prerogative to lead these forces on South Korean soil in wartime. One of the conditions for such a transfer is that the South Korean military meet certain benchmarks when it comes to its military capabilities.

Addressing this point, Kim was open about Seoul’s desire to deploy such satellites into low-Earth orbit, but he also made clear that existing liquid propellant–based launch vehicles are uneconomical for this application. South Korea’s strategic goal, per Kim, is to realize persistent space-based surveillance of North Korea, granting Seoul what he referred to as an “unblinking eye.” In July 2020, the commercial firm SpaceX launched South Korea’s first exclusive military communications satellite, the Army Navy Air Force Satellite Information System-II (ANASIS-II).

Other countries make varied use of solid-propellant SLVs for varied payload delivery to low-Earth orbit when conducting commercial and state-run space activities. Liquid-propellant boosters can be more energetic and efficient, so they tend to be favored for most missions. In the United States, repurposed solid-fueled LGM-118 Peacekeeper ICBMs are used for delivering certain government payloads to low-Earth orbit. Similarly, China’s Kuaizhou-11 program is somewhat unique in how it uses a vehicle called a transporter erector launcher to facilitate mobile launches of light satellites (an approach that could be employed for purposes such as enabling the rapid replacement of satellites that may be lost to anti-satellite weapons during a conflict).

Future launches of surveillance satellites would reduce Seoul’s dependence on U.S. technical surveillance capabilities to monitor North Korean activities and help the South Korean military achieve conditions-based OPCON transfer.[2] (After several delays, the current timeline for such a transfer is set for 2022.) Shortly before the announcement of the updated guidelines, U.S. Secretary of Defense Mark Esper and his South Korean counterpart Jeong Kyeong-doo “expressed their unwavering support for a conditions-based OPCON transition, consistent with the bilaterally-agreed Conditions-Based OPCON Transition Plan,” according to a Pentagon statement.

The latest July 2020 revision to the guidelines will facilitate these goals and was largely driven by Seoul’s space-based ISR ambitions. However, some analysis on the latest revision suggests that Seoul may now seek to build larger-diameter, longer-range solid-propellant rockets to possibly hold at risk targets in North Korea and perhaps even in China. North Korea historically has been and continues to be the primary driver of South Korea’s missile program.

During previous rounds of bilateral consultations with the United States, South Korean officials sought to ideally win approval to possess 1,000-kilometer-range missiles—capable of reaching almost all of North Korea from the island of Jeju off the southernmost tip of South Korea. New, heavy-payload ballistic missiles already in development could range much farther than 800 kilometers with a lighter payload, so South Korea already technically possesses the capability to reach all of North Korea with a 500-kilogram payload. The chief constraint preventing Seoul from officially unveiling and deploying this capability remains the bilateral missile guidelines. Although Seoul could repurpose these capabilities to hold at risk targets in northern China and parts of eastern China, South Korea holds quite nuanced views of China and does not view it as a major categorical threat, making this outcome unlikely.

New South Korean Ballistic Missile Developments

What should moderate any immediate concerns on the possible consequences of South Korea’s shift to solid-propellant SLVs is the primary concern hiding in plain sight. South Korea continues to develop solid-propellant ballistic missiles that are already capable of not only reaching all of North Korea but of doing so with heavy conventional payloads. The Hyunmoo-4 is an 800-kilometer-range system that entered testing for the first time earlier in 2020. Moon applauded it recently for exhibiting “close to the world’s heaviest warhead weight,” making full use of the 2017 update to the missile guidelines. While this missile is thought to feature a 2,000-kilogram payload, if it were to be launched with a payload half that weight, the Hyunmoo-4 would perform as a medium-range missile (using the U.S. government definition of missiles with ranges between 1,000 and 3,000 kilometers).

Little is known authoritatively about the Hyunmoo-4 beyond the fact that it entered testing this year. Its reported payload weight has appeared in multiple South Korean press reports and is consistent with the general direction of the Hyunmoo program under ADD’s auspices. For instance, the Hyunmoo-2Calso an 800-kilometer-range system, but with a smaller payload—was publicized during testing in 2017 at the height of tensions on the Korean Peninsula.

ADD emphasized the system’s earth-penetrating warhead and its precision. The suggestion was that this capability would be useful in striking tunnel-based missile launchers, hardened command-and-control targets in North Korea, or perhaps even Kim Jong Un himself. The Hyunmoo-4 appears to be a bigger and more explosive version of the Hyunmoo-2C: this new model is capable of executing that same mission against ever-harder targets that would necessitate more explosive power.

In the near term, South Korea is likely to continue investing in the Hyunmoo-4 program. This system represents the most serious challenge to the spirit of the principles that drove the missile guidelines, which were first implemented in 1979 and were primarily concerned with building confidence that South Korea could not build plausible nuclear-delivery systems. (Seoul’s indigenous nuclear weapons program had ended in the mid-1970s.)

The guidelines were designed—and updated in 2001 and 2012—with the understanding that it is reasonable to control missile capabilities by manipulating either payload or range limits. For a given payload constraint (500 kilograms, for example), extending range limits would allow Seoul to develop new boosters, but only to a point. With the scrapping of payload limits altogether in 2017, the Hyunmoo-4 was allowed to surface, raising the specter of possible longer-range South Korean systems. Seoul’s apparent acquisition of some components from older Russian ICBMs has left lingering concerns that South Korea may seek longer-range missile capabilities.

In today’s context, these concerns deserve to be taken seriously. Although South Korea continues to abide by its obligations under the Nuclear Non-Proliferation Treaty, and though its government leaders do not seek nuclear weapons, the growth of North Korean nuclear capabilities in the last five years combined with growing unease about the credibility of U.S. alliance assurances in the Trump era have renewed debates in Seoul on pursuing nuclear weapons capabilities in the future.

The military balance on the Korean Peninsula has changed dramatically since 1979, when South Korea’s missile ambitions outranged those of North Korea, which at the time had yet to flight-test its first Scud missiles. Despite this—in the spirit of the original 1979 guidelines, which sought to assuage concerns about South Korean nuclearization in the 1970s—Seoul should transparently help build confidence that its existing missile programs are no cause for concern beyond contributing to necessary conventional deterrence vis-à-vis North Korea. This confidence building would have salutary effects on regional stability amid intensifying geopolitical competition between the United States and China.

Next Steps

South Korea’s expanding space launch ambitions, sealed by the July 2020 revisions to the bilateral missile guidelines, need not heighten Northeast Asian insecurity. Seoul’s interest in more economical space launch activities and an expanded space-based layer of military surveillance is understandable. South Korean measures to increase transparency, however, could reduce the chance of misperceptions about Seoul’s intentions. Similarly, South Korea could help build confidence around its ongoing missile programs.

To mitigate a worsening security dilemma with Pyongyang and potentially Beijing, Seoul should declare the scope of applications for government-sponsored research and development in larger solid rocket boosters. While publicizing existing capabilities, like the Hyunmoo-4, may be undesirable due to the current South Korean government’s inter-Korean diplomatic efforts, Seoul can do so without provocative messaging (such as threatening North Korea with decapitation attacks or strikes on hardened military sites).

Beyond this, South Korea should also transparently release plans for specific KARI-led civilian spacefaring projects and military satellites that may make use of larger solid-propellant boosters. Such transparency would reinforce Seoul’s stated plans and build confidence. At a higher level, the South Korean government should take steps to clarify its ongoing commitment to the terms of the MTCR and the Hague Code of Conduct Against Ballistic Missile Proliferation.

Meanwhile, as testing of the Hyunmoo-4 continues, South Korea should limit development on larger payload conventional missiles that could technically be compliant with the 800-kilometer-range restriction in the bilateral missile guidelines.

Separately, the United States and South Korea should work to build confidence in the region that the 2017 and 2020 changes to the guidelines will not adversely affect regional stability. To this end, they should open an ongoing bilateral consultative review of the missile guidelines. While Seoul is not seeking further changes to the guidelines, it would be productive for the allies to establish a semiannual or quarterly review of the guidelines and discuss related matters, including any issues of concern stemming from South Korean missile activities and civilian rocket research.

South Korea has seen its security environment deteriorate sharply over the last decade as its northern neighbor has reached significant missile and nuclear milestones. Meanwhile, political malaise over cost-sharing has begun to seep into the foundations of the bilateral alliance with the United States since 2017. In this environment, precision strike missiles and a robust, indigenous space-based constellation of military surveillance satellites can plug important perceived gaps in conventional deterrence and even hedge against plausible shifts in how the United States postures its forces on the Korean Peninsula.

But Seoul’s ability to now use solid-propellant boosters to deliver satellite payloads to low-Earth orbit should not be the primary concern in the short term. Given the already impressive capabilities embodied in the Hyunmoo-4 and its predecessor, South Korea has already made itself stand out as a leader in missile technology. But as Seoul embarks into a new era as a spacefaring nation, it should take precautions to dispel concerns about its intentions and work to build confidence while practicing effective deterrence against North Korea.


1 The Trump administration withdrew from this treaty, citing a Russian missile in violation of its terms. When signed, the treaty banned the United States and the Soviet Union (and later Russia, Belarus, Kazakhstan, and Ukraine) from possessing, building, or testing ground-launched ballistic and cruise missiles with ranges between 500 and 5,500 kilometers.

2 Advanced ISR and precision-strike capabilities play a particularly important role in South Korea’s Kill Chain and Korea Massive Punishment and Retaliation strategies. The two, along with the Korea Air and Missile Defense, are sometimes referred to as the K3 suite of capabilities that, once completed, will allow for OPCON transfer. Once completed, command of the bilateral Combined Forces Command will transition to a South Korean general, with a U.S. military general taking on the role of deputy commander.