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UpdatedJune 11, 2021
Hypersonic Missile Defense: Issues for Congress
The Missile Defense Agency (MDA) and Space
Development Agency (SDA) are currently developing
elements of a hypersonic missile defense systemto defend
against hypersonic weapons and otheremerging missile
threats. These elements include the tracking and transport
layers of the National Defense Space Architecture (NDSA)
and various interceptor programs. As MDA andSDA
continue to develop these systems, Congress may consider
implications for oversight and defense authorizations and
appropriations.
Background
Hypersonic weapons, like ballistic missiles, fly at speeds of
at least Mach 5, orroughly 1 mile per second. Unlike
b allis tic mis s iles, hypersonic weapons do not follow a
b allis tic trajectory and can maneuver en route to their
target. Rus sia reportedly fielded its first hypersonic
weapons in December 2019, while some experts believe
that China fielded hypersonic weapons as early as 2020.
The United States is notexpected to field hypersonic
weapons before 2023. (For an overview ofhyp ersonic
weapons programs in Russia, China, and theUnited States,
see CRS Report R45811, Hypersonic Weapons:
Background andissues for Congress, by Kelley M. Sayler.)
The maneuverability and low flight altitude ofhypersonic
weapons could challenge existing detection and defense
systems. For example, most terrestrial-basedradars cannot
detect hypersonic weapons until late in the weapon's flight
due to line-of-sight limitations ofradar detection. This
leaves minimal time for a defender to launch interceptors
that could neutralize an inbound weapon. Figure 1 depicts
the differences in terres trial-based radar detection timelines
for ballistic missiles versus hypersonic weapons.
Figure I. Terrestrial-Based Detection of Ballistic
Missiles vs. Hypersonic 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,
https://www.economist.conVscience-an d-tec hn ology/201 9/04/06/
glid ing-missiles-that-fly-faster-than-mac h-5 -are-coming.
U.S. defense officials have stated that both existing
terrestrial- and space-based sensor architectures are
insufficient to detect and trackhypersonic weapons; former
Under Secretary of Defense for Research and Engineering
Mike Griffin has noted that hypersonic targets are 10to 20
times dimmer than what the U.S. normally tracks by
satellites in geostationary orbit.
National Defense Space Architecture
SDA developed the NationalDefense Space Architecture to
unify and integrate next generation capabilities across [the
Department of Defense (DOD)] and industry. The NDSA
aims to be a single, coherent proliferated space
architecture with seven lay ers, which include the data
tracking and transport layers depicted in Figure 2 and
discussedbelow. Otherlayers includethe custody layer to
support the targeting of mobile ground assets; the battle
management layer to provide space-based command and
control; thenavigation layerto provide alternate
positioning, navigation, and timing for potential GPS-
denied environments; the deterrence layer to detect
potentially hostile actions in deep space; and the support
layer to facilitate satellite operations for the other NDSA
layers. Once fully fielded, as is planned by 2025, the NDSA
would encompass 550 s atellites andprovide full global
coverage.
Tracking Layer
SDA began theprocess of building the tracking layer-
which is to provide global indications, warning, tracking,
and targeting of advanced missile threats, including
hypersonic mis sile systems-through the Tracking
Phenomenology Experiment (TPE). The TPE objective is to
develop a missile sensor algorithmcapable of tracking
hypersonic weapons. In parallel, SDA plans to develop
eight s atellites as part of a Wide Field of View (WFOV)
architecture. SDA then intends to expand this architecture
to provide global coverage. SDA requested $287.1 million
for WFOV and related capabilities in FY2022.
Working in tandemwith the SDA's tracking s atellites will
be the Hypersonic andBallistic Tracking Space Sensor
(HBTSS), previously known as the Space Sensor Layer,
which is being developed by MDA in collaboration with
SDA and the U.S. Space Force. HBTSS is to provide more
sensitive, but more limited (or MediumField of View
[MFOV]) coverage, comparedto WFOV.Forthis reason,
WFOV is intended to provide cueing data to HBTSS, which
could then provide more specific, target quality data to a
ground-based interceptor. By 2023 SDA plans to expand
the tracking layer to include70 WFOV and MFOV
s atellites, which, according to SDA director Dr. Derek
Tournear, willgive us enough coverage in low-Earth orbit
so that we can have essentially regionalpersistence. MDA
requested $256.2 million for HBTSS in FY2022.
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