https://crsreports.congress.gov
Updated August 20, 2024
Defense Primer: Hypersonic Boost-Glide Weapons
The U.S. Department of Defense (DOD) 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 FY2025 budget request for hypersonic
weapons was $6.9 billion (of a total $9.8 billion request for
long-range fires), up from $4.7 billion in FY2023. The
Pentagon declined to provide a breakout of funding for
hypersonic weapons in FY2024, but it requested a total of
$11 billion for long-range fires. Pentagon officials have
stated that hypersonic weapons 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, as
well as about 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 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 1. 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 HGV’s 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.
Hypersonic Boost-Glide Programs
United States
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 Navy and Army are known to maintain
hypersonic boost-glide 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
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 in 2016 and 2018. On December 27, 2019, the
Russian military announced that it had activated two SS-19
missiles equipped with Avangard.
Russia views the Avangard system as a part of its nuclear
retaliatory capability, ensuring that Russian missiles could
penetrate U.S. ballistic missile defenses. According to the
Pentagon’s 2022 Missile Defense Review, the United States
