BMD, GMD, MDA, ICBM, THAAD, Aegis... These are all terms that you have likely heard in recent news reports about ongoing threats of missile launches from North Korea. What would happen if a nuclear missile was launched at the United States? How would the United States respond to such a threat? These questions and more will soon be answered for you! You’re also going to learn the three key phases that every ballistic missile goes through during the process of saving us from a terrible outcome.
Luckily the U.S. has been preparing for such a threat with a collection of complex systems that are part of our Ballistic Missile Defense (BMD) system. These systems are comprised of satellite sensors, ground and maritime-based RADARs, and interceptor missiles.
3 Key Phases
Ballistic Missile Defense must address the 3 major phases of a missile threat (Fig. 1):
The boost phase includes the initial missile launch into space and lasts until the rocket engines have completed firing. The midcourse phase begins after rocket booster separation from the warhead and continues as the warhead travels through space, ending once the warhead begins re-entry into the Earth’s atmosphere. The terminal phase is when the warhead hurtles towards the designated target during Earth reentry.
The boost phase. The BMD system tracks the missile threat through all three phases of flight. Satellite infrared sensors monitor known launch areas for missile launch heat signatures. Once a launch is detected by a satellite, the missile tracking is transferred to forward-deployed RADAR systems. These systems are responsible for calculating the initial missile trajectory. The boost phase is when the missile is most visible to the BMD system.
The midcourse phase. The BMD system then transitions from boost phase to midcourse phase warhead tracking using ground-, sea-, and maritime-based RADARs. The warhead trajectory is monitored and broadcasted to the entire BMD network. The midcourse phase is the longest portion of the missile flight profile.
Midcourse tracking systems include the Raytheon TPY-2, Lockheed Martin Aegis Ashore, Lockheed Martin Long Range Discrimination RADAR (LRDR), Raytheon Air and Missile Defense RADAR (AMDR), and Lockheed Martin Aegis SPY-1 RADARs. Here’s a great video example of how the Raytheon TPY-2 RADAR works for early detection.
The terminal phase. The BMD system transitions to close-in warhead tracking as the warhead enters the terminal phase. The warhead gains speed as it enters the Earth’s atmosphere and approaches its final target. Missile accuracy is defined in terms of circular error probability (CEP), which is the area where there is a 50% chance of the missile striking. The CEP can grow through the entire missile flight phase depending on missile system performance at various stages of flight.
Some midcourse tracking systems can be used for terminal tracking of warheads. The Lockheed Martin Terminal High Altitude Area Defense (THAAD) RADAR is a terminal tracking system designed to track close-in threats. The U.S. recently deployed THAAD systems to South Korea, and THAAD systems are currently deployed in Guam protecting U.S. civilian and military assets in the region.
Combatting Ballistic Missile Threats
The U.S. has four options for addressing missile threats in the midcourse and terminal phase. Defeating a ballistic missile threat is akin to shooting a bullet travelling at 15,000 miles per hour with another bullet. Typically, decoys are released along with the warhead to confuse the tracking RADAR or interceptor systems. Warheads can also use infrared countermeasures. These tactics used by adversaries make the job of the BMD even more complicated.
The most reliable defense against ballistic missile attack is the U.S.’s Aegis Ballistic Defense (Fig. 2). The Aegis RADAR is manufactured by Lockheed Martin and integrated with the broader Command and Control and weapon systems aboard Aegis Class destroyers. The Aegis system is also available in land-based systems. The Aegis system is designed to combat short- and medium-range ballistic missiles through use of RADAR tracking and interceptor launch. The Aegis system has an approximately 80% intercept success rate.
The Ground-Based Midcourse Defense (GMD) system can be utilized during the midcourse phase of flight. The GMD system tracks initial and projected trajectory of the missile with RADAR data and then launches interceptor missiles from locations in Alaska or California. These interceptor missiles reach space and collide with the warhead. The GMD system has approximately a 50% success rate during operational testing.
The Terminal High Altitude Area Defense (THAAD) system is used to combat missile threats in the terminal phase. The THAAD system consists of a RADAR, interceptors, launchers, and a fire control system that is truck deployable. The THAAD system is designed to combat short- and medium-range ballistic missiles. The THAAD is the newest BMD system in the U.S. arsenal and currently has a 100% success rate during flight testing.
The Patriot Advanced Capability-3 (PAC-3) system is the final BMD system in that arsenal. The PAC-3 is used to combat missile threats in the terminal phase. You may be familiar with the original Patriot missile system used during the first Persian Gulf War. The Patriot system is the most mature BMD system in the arsenal. The PAC-3 system is designed to combat short- and medium-range ballistic missiles. The PAC-3 can also intercept missiles at lower altitudes than the THAAD systems.
Let’s hope we never have to make use of this technology. However, as you can see, the U.S. has put in a great amount of thought and effort into keeping us safe if a threat does approach. Thank you engineering and radars! Consider learning how to find and eliminate phase noise in RADAR and communication systems.