AAWSAP DIRD, Detection and High-Resolution Tracking of Vehicles at Hypersonic Velocities, November 2010

This Defense Intelligence Reference Document was prepared by the Defense Intelligence Agency's Defense Warning Office in fiscal year 2010 as part of the Advanced Aerospace Weapons System Applications program. It reviews how air flows around objects at subsonic, supersonic and hypersonic speeds, covering shock waves, wakes and ionization. It then compares ways to detect and track hypersonic vehicles, including radar, optical, infrared, LIDAR, infrasound and seismic methods. The report makes four recommendations, among them building a database of aircraft wake signatures and developing novel detectors.

From the source: Release of 2026-09-18 Incident: 11/20/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys how hypersonic vehicles may be detected and tracked by exploiting the physical effects they create in flight, especially shock waves, ionized gas, hot surfaces, and turbulent atmospheric wakes. The report reviews a broad set of detection methods, including radar, infrared sensing, optical imaging, LIDAR, passive radio reflection, infrasound, and seismic techniques, and argues that the most effective systems will likely combine multiple sensor types, because each captures different features of a high-speed vehicle’s passage through the atmosphere. It presents radar and infrared sensing as the strongest existing tools for operational detection, while giving particular attention to wake-based methods such as LIDAR and passive radio techniques for improving tracking, identification, and discrimination of future hypersonic aircraft. The paper identifies hypersonic vehicles as an evolving surveillance problem in which future progress will depend on better multi-sensor integration, improved wake characterization, and novel signature-exploitation techniques.

UNCLASSIFIED/fFOR. QFFIEl.t.L: Uii QD:I! X
St= 10/V
0 -~~----+--~............f--~~-~f--..........-~~-+---~~......
1.E+0l 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.H07
Re 0 =VD/v
Figure 3. Strouhal Frequency as a Function of Reynolds Number for
Flow Over a Circular Cylinder.
The high velocities present in the wake generate low pressures on the downstream side of
the projectile that pull the projectile backwards into the wake. Th is is defined as "wake" or
"form" drag and is a predominant cause of drag forces on aircraft or on any obj ect moving
through the atmosphere. The viscous forces that create the boundary layers on the surface
of a projectile also contribu t e a small amount of drag, usually referred to as "skin friction."
Boundary layers and wakes also affect supersonic flow, but the effect of shock waves tends
to be the predominant mechan ism affecting flow around supersonic projecti les. Total drag
force, Fo, exerted on projectiles or aircraft is usually summarized by th is equation:
(4)
The drag force is dependent upon the density of the air, p, the frontal area of the aircraft, Ar,
the aircraft velocity, V, and the drag coefficient, Co. The drag coefficient is a function of the
geometry of the aircraft and the two "dimensionless" groups, Mach number, M, and Reynolds
number, Reo, that relate inertial, viscous, and elastic forces in the flow:
C0 = f (Re 0 , M , geoniet ry) (5)
Drag coefficients for various types of aircraft and projectiles are obtained from theory, from
computational fluid mechanics, or, most commonly, from experiments in wind tunnels.
These coefficients are usually presented in tables or in graphical form. 5, 6, 7
SUPERSONIC FLOW
Air is predominantly made up of molecules of nitrogen (78%) and oxygen (21 %). At room
temperature, air behaves as an ideal gas where the density, p, the pressure, p, and the
temperature, T, are related through a gas constant, R, which is a property of the air. The
ideal gas law gives the relationship between these values. The gas constant for air is
R = 287 J/kg-K.
UNCLASSIFIED//FOR QlililEl.t.L: W&li ONL'l
6