The Standard Missile-3 (SM-3) is an exo-atmospheric missile defense interceptor used for theater ballistic missile defense. Part of the the Aegis Weapon System, it uses a hit-to-kill kinetic kill vehicle to intercept ballistic missiles during the midcourse of their flight path. The first Aegis BMD ships fielded SM-3 Block I interceptors in 2005, and the first Block IA interceptors deployed in 2006.1 The Navy also currently deploys a subsequent SM-3 variant, the Block IB, and is currently testing the Block IIA for future deployment. The Pentagon cancelled plans for an additional Block IIB version in 2013. 2 All of the current SM-3 variants fire from Mk 41 Vertical Launching System (VLS) cells on both Aegis-equipped ships and Aegis Ashore sites.
SM-3 missiles have three-stage missiles, sharing the first two stages of the SM-2 Block IV (Mk 72 Booster and Mark 104 Dual Thrust Rocket Motor) along with a third stage solid-propellant rocket (Mk 136 Third Stage Rocket Motor) to increase velocity at atmospheric exit. The kill vehicle for the SM-3 is derived from the Lightweight Exo-Atmospheric Projectile or LEAP. It combines a kinetic warhead with a longwave infrared seeker for target discrimination as well as a divert and attitude control thruster to maneuver the kill vehicle in response to the information collected by the seeker.3 The Block IA improved upon the discrimination capability of the first deployed SM-3s by enhancing the on-board infrared seeker, and has an improved divert control system.4 The interceptors are fired using the Mark 41 VLS.
SM-3 Block IA and IB
The Block IA and IB interceptors both have a 21-inch-diameter booster stage and then a 13.5-inch diameter across the rest of their length.5 The Block IB interceptor improves upon the seeker technology on the Block IA with a two-color version and an advanced signal processor to more accurately discriminate between threatening and non-threatening objects.6 The IB also incorporates an improved Throttling Divert and Attitude Control System (TDACS), which gives the kill vehicle better ability to maneuver as it closes in on the target.7 The Block IB finished testing and was declared operationally ready after FTM-22 in 2013. The Missile Defense Agency began procurement in FY 2014.8 The Block IB interceptor is the primary interceptor for the Aegis Ashore site in Romania, fielded as part of Phase 2 of the European Phased Adaptive Approach.
SM-3 Block IIA
The Block IIA, the result of a cooperative development project of the United States and Japan, has a uniform 21-inch diameter to accommodate more rocket fuel, which allows for a higher burnout velocity, allowing the interceptor to travel farther and intercept missiles travelling at faster speeds. This expands the range of the system and the number of targets it can engage. 9 The Block IIA also incorporates a more sensitive sensor seeker, more divert capability, and longer operating time for its upgraded kill vehicle.10 The Block IIA conducted its first two flight tests in 2015, and the Japan and the United States conducted the SM-3 IIA’s first successful intercept test on February 3, 2017.11
The cancelled Block IIB interceptor would have consisted of a wider booster rocket, requiring modifications to the existing Aegis launcher systems, to create even higher burnout velocities to potentially intercept intercontinental-range ballistic missiles. This interceptor was intended for deployment in Phase 4 of the European Phased Adaptive Approach, but was cancelled in March 2013. The IIB program was then eliminate in favor of research and development into the Common Kill Vehicle (CKV), a project to develop technologies for both Standard Missiles and Ground-based Interceptors. 12
According to the MDA FY 2016 budget request, at the end of FY 2015, 210 SM-3 interceptors will have been delivered with MDA holding an inventory of 165. 13 The budget for FY 2016 would push those numbers to 257 and 193 respectively, consisting of 150 delivered and 101 inventoried Block I/A interceptors and 107 delivered and 92 inventoried Block IB interceptors, and the FY 2017 budget would increase those numbers to 296 delivered interceptors consisting of 150 Block I/A and 146 Block IB, with 213 in the inventory consisting of 85 Block I/A and 128 Block IB interceptors. 14 As a result of the Bipartisan Budget Act of 2015, the FY 2016 procurement of SM-3 Block IB interceptors was cut by $30 million, likely cutting three interceptors at the estimated $10 million cost each.15 In December 2015, the Pentagon issued a contract to procure 52 SM-3 Block IB interceptors with FY 2015 funds with the option to procure up to that many interceptors every fiscal year until 2018.16 After the successful second flight test of the Block IIA in December 2015, MDA contracted to purchase 17 interceptors, which are scheduled for delivery by FY 2019.17
SM-3 Anti-Satellite Role
The 2008 Operation Burnt Frost intercept of a non-functional reconnaissance satellite demonstrated that SM-3 interceptors could be used to conduct anti-satellite missions if required. The expanded range of the Block IIA interceptors would allow them to reach even higher orbit satellites should they be used for such a mission. Concerns about the amount of debris in low earth orbit created by a kinetic collision with a satellite wold limit the utility of this application, however, as it could also affect the functioning of U.S. satellites.18