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1 [1] (March 19, 2024)

handle is hein.crs/goveorl0001 and id is 1 raw text is: Congressional Research Service Informing the Iegislative debate since 1914 0 Updated March 19, 2024 Defense Primer: LGM-35A Sentinel Intercontinental Ballistic Missile The LGM-35A Sentinel is an intercontinental ballistic missile (ICBM) system that is expected to replace the Minuteman III (MMIII) ICBM in the U.S. nuclear force structure. MMIII has served as the ground-based leg of the U.S. nuclear triad-land-based ICBMs, submarine- launched ballistic missiles, and nuclear-capable bombers- part of the U.S. nuclear deterrent since 1970. The Sentinel program encompasses the missile and its associated infrastructure, including silos, communication equipment, and facilities for launch control, maintenance, and weapons storage. The Department of Energy's National Nuclear Security Administration (NNSA) is also developing a W87-1 warhead for the missile. The Biden Administration endorsed the program in its 2022 Nuclear Posture Review (NPR), which says Sentinel will replace the MMIII missiles one-for-one to maintain 400 ICBMs on alert. Since the FY2017 NDAA, Congress has required that no less than 400 on-alert U.S. ICBMs be deployed. The Administration included $3.7 billion for the program in its FY2025 Department of Defense (DOD) budget request. The NNSA FY2025 budget request included $1.1 billion for the W87-1 program. What Is an IC BMI The United States began deploying nuclear-armed ICBMs in 1959, and has maintained these systems on alert, or able to launch promptly, since that time. The Air Force has tested MMIII missiles to a range greater than 6,000 miles, or 5,000 nautical miles. Although some countries use road or rail mobile launchers for their ICBMs, the United States bases its ICBMs in hardened concrete silos, known as launch facilities, located in North Dakota, Montana, Wyoming, Colorado, and Nebraska. An ICBM can reach targets around the globe in approximately 30 minutes after launch. During the first three minutes, three solid fuel rocket motors power the missile's flight. After the powered portion of flight, the missile follows a parabolic trajectory toward its target. It releases its warhead during the mid-course portion of its flight, and the warhead continues to the target. Once the President authorizes the launch of any U.S. nuclear-armed missile, it cannot be recalled or destroyed in flight. The same is true for nuclear missiles launched from U.S. submarines. In contrast, U.S. bombers can return to their bases after launch, without releasing their weapons, although the weapons cannot be recalled after their release from the bomber. The Transition from Minuteman :11 The U.S. Air Force first deployed Minuteman ICBMs in the 1960s. MMIII, the first of the class to carry multiple warheads, entered the force in the early 1970s. The Air Force has replaced and updated many of the component systems on the missile-a process known as life- extension-several times over the past 50 years. The most recent life-extension program included, among other things, a replacement booster and a new missile guidance computer. The Air Force has noted that both of these components may face reliability concerns as they reach the end of their intended lifespans over the next decade. After conducting a comprehensive Analysis of Alternatives in 2014, the Air Force determined that it would replace MMIII with a new missile system. The Air Force argued that when compared with a life-extended MMIII, the new missile would meet current and expected threats, maintain the industrial base, insert more reliable technology, produce a modular weapon system concept, and reduce life cycle cost. Air Force officials have stated that the Sentinel would have numerous advantages to MMIII. These include the following: The use of a modular design and open architecture that would reduce cost and provide flexibility for improvements throughout the life of the weapon system. Open systems architectures would allow the Air Force to control the intellectual property of the system, including the system's source code, enabling the Air Force to complete future upgrades and improvements. The modular design, in turn, would also allow maintenance in ways that mitigate security risks and potentially enabled a reduction in the number of required security forces. The increased throw weight of the Sentinel compared to the MMIII, due to the use of much lighter composite material, would allow the new missile to carry different payloads. As adversaries develop ballistic missile defenses in the future, the increased throw weight, which is a measure of the weight of the payload that the missile can deliver to a particular range, could potentially allow the Air Force to develop countermeasures that would help the missile overcome the defenses. The Air Force planned for the Sentinel (originally Ground Based Strategic Deterrent, or GBSD) to begin replacing MMIII in 2029 and to complete the deployment in 2036.