Last summer, the Nonproliferation Policy Education Center (NPEC) held a three-move space war game that focused on North Korea’s potential use of nuclear weapons in low-earth orbit or near-space to knock out low-Earth orbit satellites. Initially, the game’s participants found this possibility a bit fantastic. Mid-way through the game, though, they warmed to the idea. Some even suggested that China might exercise the option.

That was prescient. Twelve weeks after NPEC completed its simulation, the South China Morning Post reported that the People’s Liberation Army’s Northwest Institute of Nuclear Technology was simulating nuclear weapons strikes designed to knockout dual-use satellite constellations, such as Starlink. The stated aim of the computer-simulated attacks was to prevent Taiwan from exploiting such militarily useful commercial systems. The article noted that the Limited Test Ban Treaty prohibits the detonation of nuclear weapons in space and the atmosphere. It failed, however, to point out that neither China nor North Korea are parties to the treaty. Similarly, neither the United States nor China have yet ratified the Comprehensive Test Ban Treaty.

Since the publication of the South China Morning Post article, Beijing’s efforts to game operations in near-space with lighter-than-air vehicles has strained relations with Washington and raised concerns about China’s offensive strategy for near-space operations generally.

What unfolded in NPEC’s war game last summer, then, is not all that far-fetched. By the end of the decade (when this simulation’s war takes place), tens of thousands of small, commercial, networked satellite systems will be flying in low-Earth orbit. These satellites will complement the U.S. Defense Department’s own space architecture, which includes national security systems flying in low, medium, and geosynchronous orbits. Hostile states, like North Korea, will want to hold them at risk.

What’s the worst they might do? They could wipe out nearly all the satellites in low-Earth orbit. Why bother with such an extreme prospect? It’s a prerequisite for sound planning: to hedge against the worst and to deal with lesser included threats, military planners and policymakers often focus on dire hypotheticals—e.g., massive nuclear wars, global warming catastrophes, pandemics, and so on. U.S. space policymakers arguably don’t yet have such an organizing disaster.

What the War Game Covered

The war game NPEC designed and played begins in the spring of 2029. The DPRK tests an inter-continental ballistic missile that inadvertently flies further than intended, triggering U.S. missile defenses in Alaska. No interception is made, but the United States demands North Korea show a good-faith effort to avoid further provocations by garrisoning its mobile missile force. Washington orders reconnaissance flights near North Korea and subsequently asks the United Nations to approve a selective blockade of North Korea while placing U.S. strategic forces on Defcon 3.

North Korea refuses America’s demands, begins to mobilize, and warns Washington that if the United States fails to end its alert and refuses to schedule the removal of its troops from South Korea (ROK), war will ensue. Tensions continue to build. Then early in June, North Korea launches a satellite into orbit and warns of a possible nuclear explosion in space unless the U.S. and ROK stand down. Washington contacts Beijing in hopes of getting China to pressure the North Koreans to relent. Chinese officials counsel Washington to negotiate with Pyongyang directly, noting that North Korea has not yet violated any treaty. The United States goes to the UN Security Council with a sanctions resolution against Pyongyang. Russia and China block its approval.

Throughout this crisis, U.S. officials try to determine if North Korea’s satellite is carrying a nuclear payload but are unable to do so. In mid-June of 2029, North Korea launches another payload into space, this time over the North Pacific. Well before it enters full orbit, the payload detonates, releasing 10–20 kilotons of nuclear energy into low-Earth orbit. All satellites in line of sight of the explosion are immediately disabled. U.S. space experts predict that the rest of the world’s satellites in lower low-Earth orbit will be disabled in a matter of days to several weeks. Shortly after the detonation, North Korea invades South Korea.

At each move, the game focused on what the United States and its closest space-faring allies would do to deal with each of these crises. This produced four takeaways:

1. Popular notions that space warfare will stay in space and that international limits can prevent hostile actions from occurring there are both strong and wrong.

Diplomats hope that with enough rules of the road, norms, and diplomatic signaling, the worst in space—military combat—can be avoided. Yet the strong belief that diplomatic limits might prevent hostile military actions in space is betrayed by deep ambiguities in the space laws and regulations we have. In this regard, the U.S. team insisted North Korea’s nuclear detonation violated the Outer Space Treaty (OST). China, however, disagreed, as did U.S. Department of Defense legal experts: unless it can be proven that a nuclear device detonated while it was clearly in orbit or “on station,” there may be no foul play. Indeed, under the OST a state may legally inject a nuclear weapon into space with a missile and detonate it so long as the warhead does not fly at least one, complete Earth orbit.

Unfortunately, there is nearly no easy way to verify if an orbiting spacecraft is carrying a nuclear warhead nor is there any simple way to enforce the OST’s ban on “stationing” or detonating nuclear weapons in space until the treaty itself is violated with a detonation. It also is unclear in the game if the detonation occurs when North Korea is in a clear state of war, in which case, the OST’s stipulations may not apply. This suggests that space diplomacy’s first task regarding these issues is to clarify what disagreements we are likely to have with hostile states rather than to insist that they will not arise or to “fix” them by treaty negotiations.

For decades, the United States and its allies have sought to establish clear rules whose violation has consequences. Although desirable, this in many key instances is still unattained. NPEC’s previous China space game struggled with this as well and concluded that only rules that could be self-enforced would likely be of any utility. Unfortunately, nothing in this game suggested otherwise. As for the plausible hawkish hope that with enough investments in military space capabilities, combat there can be deterred or, at least, be prevented from leading to conflict on Earth, the game itself was inconclusive.  At the same time, the hope that avoiding “combat” operations in space will somehow protect us, was discredited.

2. Developing satellite hardening and constellation reconstitution options to respond to a nuclear detonation in space are obvious hedges; far less obvious is what should be done to secure such options.

All of the game’s players agreed that, after a high-altitude nuclear explosion, there would likely be a race to reconstitute one’s satellite constellations. There also was significant agreement about what should be reconstituted—satellites and launchers—and how—by stockpiling certain materials, satellites, launchers, and other items, as well as ramping up manufacturing and mobilization base, etc. There was far less agreement or consideration, however, about when to reconstitute early, when satellite lifetimes would be limited, or later, after the radiation levels in the Van Allen Belts had declined, allowing newly inserted satellites to  survive longer. Nor was there agreement about where to focus the reconstitution efforts—in upper low-Earth orbit, medium-Earth orbit, in geosynchronous-Earth orbit, or on alternative, non-space-based, terrestrial and near terrestrial systems (high-altitude drones and balloons, undersea communications cables, ground-based navigational systems, etc.).

It also was unclear who might win in such a reconstitution race—China or the United States—and why. Some believed that the United States and its allies had a launch, satellite infrastructure, and technology lead as well as a larger mobilization base than China. Others believed China would steal a march on the race given its much quicker acquisition times. The game also stumbled across another reconstitution problem. Most players supposed that the Russian Soyuz capsule would be available on the U.S. space station in 2029. It might not. Developing U.S. or allied escape capsules would be desirable for both government and commercial space stations and operations on the moon.

Finally, there was disagreement about how much hardening should be required of commercial satellite operators. Some said it was pointless to demand this of commercial space firms, that if the U.S. government did, these firms would simply go overseas. Others said hardening should be proportionate to the risk being run—is the satellite in low-Earth orbit, near debris, able to cope with strong solar storms, radiation etc. Others insisted that if the commercial satellite provided government services, their government contracts could be conditioned upon meeting certain hardening requirements. Yet others said the government should help pay for such hardening. Some took the position that low-Earth orbit satellites ultimately were not that important to U.S. and allied security and prosperity. Others disagreed.

What is clear is our government should do more to resolve these disagreements before any crisis approaching anything like what unfolded during the game might occur.