This article is part of the World Economic Forum's Geostrategy platform

Improvements in North Korea’s nuclear and long-range missile programmes have led the Trump administration and the United States Congress to resurrect plans for interceptors in space.

The 2018 National Defense Authorization Act instructs the director of the Missile Defense Agency to ‘develop a space-based ballistic missile intercept layer to the ballistic missile defense system’ consistent with the recommendations of a yet-to-be-released Missile Defense Review. The interceptor is likely to be targeted at North Korean ballistic missiles in the boost-phase of flight.

The potential use of space-based weapons to defend the US from ballistic missiles is not a new concept. Under president Ronald Reagan, the Strategic Defense Initiative (SDI) envisaged layers of space-based weapons capable of rendering nuclear weapons obsolete. With the collapse of the Soviet Union, George H. W. Bush opted to downscale the project and focus on the development of a kinetic space-based intercept layer known as Brilliant Pebbles. However, questions of cost, technological feasibility and the lack of a viable long-range missile threat prompted the Bill Clinton administration to cancel Brilliant Pebbles and related programmes.

Key questions

The prospect of introducing a space-based layer of interceptors raises legal, political, fiscal and technological questions. Although there are no specific legal obstacles to fielding space-based interceptors, the US will have to justify that they are within the scope of the ‘peaceful purposes’ established in Article IV of the Outer Space Treaty (OST),which prohibits states from stationing weapons of mass destruction in space.

The 1972 Anti-Ballistic Missile (ABM) Treaty, which banned both the US and the Soviet Union from deploying interceptors in space, ceased to be applicable after President George W. Bush withdrew the US from the treaty in 2002.

Presently, there is no other specific international law that bans states from deploying conventional weapons in space, including the use of interceptor missiles.

Is an arms race in space inevitable?

Historically, Washington and Moscow have benefited from military restraint in space. While both countries developed anti-satellite (ASAT) weapons as part of a ‘hedging’ strategy, neither opted to deploy such weapons in space. Yet, the US and the Soviet Union continued to conduct research, development and some testing of ASAT technologies; and more recently, China began exploring this capability as well.

There are several varieties of ASAT weapons, such as direct-ascent, co-orbital, non-kinetic, jamming and cyber. Only non-kinetic ASAT weapons are used in military operations today, but it is possible that more ASAT technologies will be used for military operations in the near future.

Among these, co-orbital ASAT weapons can be deemed as a clear step to space weaponization because they are deployed into orbit and attack a target satellite.

Moreover, some ASAT technologies are not prohibitively expensive or too technologically advanced for multiple nations – or perhaps even non-state actors – to obtain. For example, North Korea’s missiles have enough range to attack satellites in low Earth orbit, and Iran has used electromagnetic jamming and spoofing to hinder satellite signals.

If the US decides to field space-based interceptors, it will upset the status quo by breaking with the taboo of weaponizing space. Such moves could provide a rationale for other actors to exploit this domain, creating an arms-race dynamic among major space powers. The introduction of ASAT weapons by capable powers would likely follow.

Some may argue that the weaponization of space is inevitable given the number of countries interested in accessing and exploiting this domain. The US, according to this argument, should take the lead and advance its interests before its adversaries decide to take advantage of a reluctant America. Others will urge restraint, highlighting the advantages brought about by the OST and ABM treaties.

The rationale for space-based weapons

While the wisdom for placing weapons in space can be debated, it is important to realize that there are no significant technological barriers to developing space-based interceptors. But this does not mean that these weapons are efficient or cost effective.

One expert has calculated that hundreds of interceptors orbiting above the Earth are needed to provide boost-phase defence against a small territory the size of North Korea.

The cost of procuring, orbiting and maintaining an interceptor layer designed specifically for North Korea is likely to exceed US$100 billion. If the US aims to erect a more ambitious space-based interceptor architecture that provides defence against ballistic missiles launched from anywhere on the globe, the number of interceptors required becomes prohibitively expensive.


Finally, even if the US overcomes these challenges, space-based interceptors would remain vulnerable to guided missiles launched from the ground.

Because the interceptors must orbit at low altitudes of 200 km or less when above the anticipated launch location, and because they travel along predictable orbits and can be easily tracked using radars, an adversary capable of developing long-range missiles could almost certainly build a ground-based ASAT weapon.

Force protection of the space-based interceptor layer is therefore likely required, adding more cost and complexity to the system. Maintenance of space-based interceptors also poses an operational and fiscal challenge.

Furthermore, instead of the space-based interceptor, there are arguments for alternative options, including the potential use of uninhabited aerial vehicles armed with lightweight, high-speed interceptors to fortify the ballistic missile defence (BMD) system.

A space-based interceptor constellation, if deployed, would undoubtedly strengthen the current US BMD. Beyond the additional defensive tier, boost-phase interceptors offer advantages over their mid-course and terminal phase counterparts, because the intercepts would occur before the missile releases its warheads.

However, to create a space-based intercept layer, policymakers will have to address many issues first. The risk that space-based interceptors could lead to a new arms race in space should be considered carefully.

Will space-based missile interceptors weaponize space? Michael Elleman and Gentoku Toyoma, the International Institute for Strategic Studies