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1 [1] (December 1, 2020)

handle is hein.crs/govdcsc0001 and id is 1 raw text is: Updated December 1, 2020 Defense Primer: Hypersonic Boost-Glide Weapons The U.S. Department of Defense is pursuing two types of hypersonic weapons technologies: boost-glide systems that place a maneuverable glide vehicle atop a ballistic missile or rocket booster, and cruise missiles that would use high- speed, air-breathing engines known as scramjets to travel to hypersonic speeds. This In Focus addresses only the first of these technologies. The Pentagon's FY2021 budget request for hypersonic- related research is $3.2 billion up from $2.6 billion in the FY2020 request including $206.8 million for hypersonic defense programs. This increased funding and statements from Pentagon officials demonstrate growing support for weapons that could attack priority targets promptly and with improved accuracy without facing defeat by an adversary's air or missile defense systems. Pentagon officials have also expressed concerns about advances in hypersonic weapons technologies in Russia and China, and on the potential threats to U.S. forces, allies, and territory. Hypersonic glide vehicles (HGVs), like all weapons delivered by medium- and longer-range rocket boosters, can travel at speeds of at least Mach 5, or about 1 mile per second. The key difference between missiles armed with HGVs and missiles armed with ballistic reentry vehicles (i.e., those that travel on a ballistic trajectory throughout their flight) is not their speed, but their ability to maneuver and change course after they are released from their rocket boosters. In addition, although it is not necessary, many concepts for the delivery of HGVs presume that the boosters will launch along a flatter, or depressed, trajectory than standard ballistic missiles, and will release their gliders at a lower altitude of flight (see Figure 1). Figure I. Flight Trajectory of Ballistic Missiles vs. Hypersonic Boost-Glide Weapons Source: CRS image based on an image in Gliding missiles that fly faster than Mach 5 are coming, The Economist, April 6, 2019. Taken together, the HGVs' novel trajectory and maneuverability in flight would complicate a U. S. effort to detect, track, and defend against an attack. The United States would likely detect the booster's launch, as it would for the launch of any ballistic missile, but it would not be able to predict the HGV's flight path. In addition, although an HGV launched by a rocket booster would reach its target far more quickly than a warhead delivered by an aircraft or subsonic cruise missile (in minutes instead of hours), it would not travel faster than a ballistic reentry vehicle. However, it would be more difficult to predict the intended target and to direct missile defense interceptors toward the attacking HGV. When the United States began to assess the military utility of hypersonic boost-glide weapons in the early 2000s, it sought to develop longer-range systems that could reach deep into an adversary's territory to attack defended, hardened, and time-urgent targets. (For an overview of the history of U.S. programs, see CRS Report R41464, Conventional Prompt Global Strike and Long-Range Ballistic Missiles: Background and Issues, by Amy F. Woolf.) More recently, the Pentagon has increased funding and accelerated development programs for shorter and intermediate-range boost-glide systems that could conduct prompt attacks against heavily defended targets in regional conflicts. The Department of Defense (DOD) is developing hypersonic weapons under the Navy's Conventional Prompt Strike program, as well as through several Air Force, Army, and DARPA programs. (Details on these programs can be found in CRS Report R45811, Hypersonic Weapons: Background and Issues for Congress, by Kelley M. Sayler.) Unlike Russia and China, the United States is not developing HGVs for use with nuclear warheads. As a result, U.S. gliders may require greater accuracy and will be more technically challenging to develop than nuclear-armed Chinese and Russian systems. Russia's HGV, known as Avangard, is equipped with a nuclear warhead and deployed on SS-19 long-range land- based ballistic missiles. While SS-19 missiles can carry six nuclear warheads on a ballistic trajectory, reports indicate that they will deploy with only one Avangard HGV. Avangard reportedly features onboard countermeasures and will be able to maneuver in flight so that it can evade U. S. ballistic missile defenses. Russia conducted successful tests of Avangard 2016 and 2018. On December 27, 2019, the Russian military announced that it had activated two SS-19 missiles equipped with Avangard. F \\\\'\\ \ \N \ \I \N,\ \\ \ \ Q\\ \\\ \\\