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1 [1] (June 8, 2021)

handle is hein.crs/govedpc0001 and id is 1 raw text is: C s I Aesesroh Serwco kd arnir~j lb ~ I ~jkbt ~ d~tate i~ri~ W 14 Updated June 8, 2021 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 travelto hypersonic speeds. This In Focus addresses only thefirst of these technologies. The Pentagon's FY2022 budgetrequest for hypersonic- related research is $3.8 billion-up from $3.2 billion in the FY2021 request. This increased funding and statements from Pentagon officials demonstrate growing support for weapons that could attackpriority targets promptly and with improved accuracy withoutfacing defeatby an adversary's air or missile defense systems. Pentagon officials have also expres sed concerns about advances in hypersonic weapons technologies in Rus sia and China, and on the potential threats to U.S. forces, allies, and territory. Characteristics of Hypersonic Glide Vehicles Hypersonic glide vehicles (HGVs), like all weapons delivered by medium- and longer-range rocket boosteis, can travel at speeds of at least Mach 5, or about 1 mile per second. The key difference between mis siles armed with HGVs and missiles armed with ballis tic reentry vehicles (i.e., thosethat travelon a ballistic trajectory throughout their flight) is not their speed, but their ability to maneuver and change course after they are released fromtheir 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 standardballistic missiles, and willrelease theirglideis 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, 201 9. Taken together, the HGVs' noveltrajectory and maneuverability in flight would complicate a U.S. effort to detect, track, and defend against an attack. The United States wouldlikely detect the booster's launch, as it would for the launch of any ballis tic missile, but it would notbe able to predict the HGV's flight path. In addition, although an HGV launched by a rocket booster would reach its taiget far more quickly than a warhead delivered by an aircraft or subsonic cruise missile (in minutes instead ofhours), it would not travel faster than a ballistic reentry vehicle. However, it would be more difficult to predict the intended target and to direct mis sile defense interceptors toward the attacking HGV. Hypersonic Boost-Glide Programs United States When theUnited Statesbeganto assess themilitary utility of hypersonic boost-glide weapons in the early 2000s, it soughtto develop longer-range systems that couldreach deep into an adversary's territory to attack defended, hardened, and time-urgent targets. (For an overview of the history ofU.S. programs, see CRS Report R41464, ConventionalPrompt Global Strike and Long-Range Ballistic Missiles: BackgroundandIssues, by Amy F. Woolf.) More recently, the Pentagon has increased funding and accelerated developmentprograms for shorter and intermediate-range boost-glide systems that could conduct prompt attacks ag ainst 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 ontheseprograms canbe found in CRS Report R45811, Hypersonic Weapons: Backgroundandlssuesfor Congress, by Kelley M. Sayler.) Unlike Russia and China, theUnited 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-amid Chinese and Russian systems. Russia Rus sia's HGV, known as Avangard, is equipped with a nuclear warhead and deployed on SS-19 long-range land- based ballistic mis siles. While SS-19 mis siles can carry six nuclear warheads on a b allis tic trajectory, reports indicate that they will deploy with only one Avangard HGV. Avangardreportedly features onboard countermeasures and will be able to maneuver in flight so that it can evade U.S. ballis tic missile defenses. Rus sia conducted successful tests of Avangard in 2016 and 2018. On December 27, 2019, the Russian military announced that it had activated two SS-19 missiles equipped with Avangard. ttps://crsreports.congre&