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.

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Re = viscous forces= VD (3)
inertial forces v
In this expression, V is the velocity of the projectile, D is its effective diameter, and v is the
kinematic viscosity of the fluid. As flow passes over the projectile in Figure 1, viscous forces
are especially strong near the surface where the velocity changes from zero at the surface of
the projectile to the free stream velocity.
Direction of Flow
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<- ________ Velocity D ibution within
Boundary Layer -- - - - - - the Bounda ayer
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Figure 1. Boundary Layer Development in Subsonic Flow About a Projectile.
The region where this transition in velocity occurs is called a "boundary layer," which grows
in thickness as flow moves along the surface from the nose to the rear of the projectile.
The boundary layer forms around the surface of the projectile and "separates" from the
surface at the back end of the projectile. Pockets of fluid spill off of the back end of the
projectile and form rotating pockets of fluid called Strauhal eddies or vortices. These eddies
"shed" from the surface at a rate that is strongly dependent upon the Reynolds number in
the flow. Figure 2 demonstrates that these eddies form a "wake" downstream of the
projectile that can extend far into the flu id.
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