Space-based missile defense: Is it better to spend money on weapons or sensors?

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SN Military.Space Sandra Erwin

The Pentagon is expected to reveal in next year’s budget its plans to move forward to deploy new missile defense systems in space. Military contractors in the space sector view this program as a major business opportunity.

Although the Missile Defense Agency has said the plan for now is to focus on sensors in space, there is speculation that the Pentagon might also consider investments in orbiting interceptor missiles to be aimed at enemy ICBMs or hypersonic vehicles.

In a new white paper, analyst Thomas Roberts of the Center for Strategic and International Studies cautions that money would be much better spent on sensors than on interceptors.

SPACE INTERCEPTORS INEFFICIENT Advocates of weapons in space argue that orbiting interceptors would provide effective defenses against missiles aimed at the United States or its allies. Roberts believes this would be a poor return on investment. If the United States were to deploy 24 satellites equipped with weapons, that number of spacecraft would not be nearly enough to provide global coverage, he argues. “When placed in a constellation to offer optimal coverage of North Korea, for example, 24 satellites would leave the Korean peninsula completely uncovered over 75 percent of the time.”

Furthermore, these satellites would pass overhead in visible, predictable paths. An adversary would know with certainty when the constellation would provide no coverage and plan attacks accordingly, says Roberts. Since any gap in coverage is effectively no coverage, any constellation that does not offer continuous coverage does not meaningfully contribute to the broader U.S. ballistic missile defense system.

Roberts contends that a constellation of 24 satellites with four interceptors apiece does not provide better boost-phase coverage than a constellation of 24 satellites with one interceptor apiece. If one interceptor cannot reach its target missile in time, neither can the other three.

Without a doubt, this would be a bad investment, he says. But the same number of satellites could provide “excellent worldwide sensor coverage.”

SENSORS IN SPACE MAKES MORE SENSE The already-deployed Space-Based Infrared System satellites track missiles in their boost phase. They are not designed to track missiles during their midcourse phase when they must be observed as relatively cold objects against the even colder background of space. After a missile’s engines burn out, the heat signature goes dark, and they cannot be easily tracked using infrared systems. A new layer in low Earth orbit could use radar or optical sensors to monitor missiles mid-flight. This is a capability the Pentagon believes would be essential to defend the United States from advanced hypersonic missiles being developed by China and Russia.

As reported recently in SpaceNews magazine, the Pentagon is studying concepts for a space sensor layer but has not yet settled on the details.

Congress inserted $73 million into the Pentagon’s 2019 budget to get a program started. The projected total cost is still unknown.

Roberts said his study was about the “physical feasibility” of interceptors or sensors in space but didn’t address the potential cost or whether the Pentagon could afford this technology. He recognized that “budget chatter supersedes the physical limitations in these discussions sometimes.”


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