The Pentagon’s missile defense review is now underway, incorporating mandates from both the White House and Congress. One of its considerations, at presidential direction, is whether there should be a relative “rebalancing” between homeland and regional missile defense. Regional defense has received a relatively greater share of the Missile Defense Agency (MDA) budget over the past decade, so increased emphasis on protecting the homeland may well be in order, especially given missile advances by North Korea, including the launch of a Hwasong-14 ICBM earlier this week. But another, crosscutting kind of rebalance may be even more important to consider: a rebalancing of the sensor architecture to the space domain. Fielding a space-based sensor layer would provide unique improvements to homeland and regional missile defenses alike.
Sensors and ground systems do not as easily capture the popular imagination, so they do not get as much attention as the interceptors themselves. Commentators typically tend to focus on the numbers and characteristics of interceptors, and understandably so. For the homeland mission in particular, improvements to the reliability, capability, and capacity of ground-based interceptors are certainly in order. Interceptors are only as good as the sensors that tell them where to go and what to kill. We currently rely almost entirely upon sensors based on sea or land. A space layer would add unique capabilities not merely to this or that interceptor, but across the entire ballistic missile defense system—including Patriot/PAC-3, THAAD, Aegis, and Ground-based Midcourse Defense (GMD).
The utility of space for this mission is no secret. Each of the last five administrations has had space-based infrared sensors as a key component of its planned missile defense architecture, at least on paper, but none has yet deployed one. Ground- and sea-based radars will and should continue to play critical roles, but the first and possibly most important step to improving global missile defense capabilities would be to create and field a space sensor layer for persistent, birth-to-death missile tracking and discrimination.