While US nuclear strategy relies primarily on the deterrence afforded through the nuclear triad, the GMD serves as an insurance policy against small-scale attacks or accidental launches.
The Ground-Based Midcourse Defense (GMD) system is the United States’ primary homeland missile shield, designed to intercept and destroy intercontinental ballistic missiles (ICBMs) in space during the midcourse phase of their trajectory (which occurs after boost and before reentry). The GMD represents the highest layer in America’s multi-tiered missile defense architecture. Crucially, it is the only system built specifically to defend the US mainland from long-range nuclear attack.
The GMD Is America’s Most Advanced Anti-Missile Defense System
Lower-altitude systems like the THAAD protect against short-range threats, particularly low-flying ballistic missiles. They might also have some value against ICBMs during their terminal phase, but cannot intercept them reliably due to ICBMs’ tremendous speed (and oftentimes their post-reentry countermeasures, such as maneuvering and decoy firing). The GMD is designed to intercept ICBMs at a much higher altitude.
Crucially, the GMD system is tailored specifically to deal with the threat of a rogue state such as North Korea or Iran firing a small number of missiles. This is the scenario envisioned in the recent Kathryn Bigelow film A House of Dynamite, in which a single ICBM of uncertain origin is fired toward the United States and the GMD must intercept it. In the event of a more conventional attack on America—if, in other words, a near-peer adversary like Russia or China fired hundreds or thousands of ICBMs at the United States—the GMD would immediately be overwhelmed. In that case, though, it would be easy to identify where the missiles came from and return fire with America’s own ICBMs before they landed, ensuring the attacker’s destruction as well.
The GMD’s goal is to detect, track, and intercept an incoming warhead while it is still traveling through space, hundreds or thousands of kilometers from US airspace and the US population. Still, while the concept is simple enough, the task itself is exceptionally complex; an ICBM travels at speeds exceeding 24,000 kilometers per hour; and the GMD interceptor must collide with the ICBM. Basically, the task calls for a bullet hitting another bullet—in space.
This is an understandably daunting challenge. The GMD system makes it possible through three main stages:
- Detection and Tracking: GMD relies on a network of early-warning radars, space-based infrared sensors, and Aegis-equipped ships to detect missile launches and calculate trajectory. Once a potential ICBM is confirmed, data is relayed to the fire-control network.
- Command and Control: The Missile Defense Integration and Operations Center (MDIOC) in Colorado coordinates data from across the global networks. The Ground-based Fire Control system then uses the compiled information to select interceptors and compute a precise engagement solution.
- Interception: The Ground-Based Interceptor (GBI) missile is launched from Fort Greely, Alaska, or Vandenburg Space Force Base, California. Each GBI consists of a three-stage solid-fuel booster topped with an Exoatmospheric Kill Vehicle (EKV). After separating from the booster in space, the EKV uses onboard sensors and divert thrusters to track and collide with the incoming warhead outside of Earth’s atmosphere. The impact releases an enormous amount of kinetic energy, destroying the incoming ICBM solely with kinetic energy, and without the use of explosives.
How Effective Is the GMD System?
While US nuclear strategy relies primarily on the deterrence afforded through the nuclear triad, the GMD serves as an insurance policy against small-scale attacks or accidental launches—the last line of defense for the US homeland. The GMD serves as much as a psychological deterrent as well as a physical one, signaling that the US retains both the capability and the political will to protect its homeland.
Still, the GMD is flawed. Its limitations include its high cost, it finite number of interceptors, and an uncertain test record. Even at best, the GMD is designed solely to counter limited threats, not massive arsenals.
While comforting to have, the GMD is a clear demonstration of just how difficult it is to defend against nuclear-warhead-tipped ICBMs. But it provides some peace of mind against rogue states, and represents a step in the evolution of better missile defense systems—like the Next Generation Interceptor (NGI) currently under development by Lockheed Martin.
About the Author: Harrison Kass
Harrison Kass is a senior defense and national security writer at The National Interest. Kass is an attorney and former political candidate who joined the US Air Force as a pilot trainee before being medically discharged. He focuses on military strategy, aerospace, and global security affairs. He holds a JD from the University of Oregon and a master’s in Global Journalism and International Relations from NYU.
Image: Wikimedia Commons.
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