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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/,SFOR. QFFIElal L: 1!ii 011! X p = pRT (6) It is possible to statistically model the motion of the molecules of oxygen and nitrogen in air, and their kinetic energy, KE, can be determined based on the mass, m, of each molecule and the temperature of the gas. KE =_!.mV 2 ='i kT 2 2 (7) In this equation, k is the Boltzmann constant (1.3807 x 10-23 J/K). We can ca lculate the velocity of air molecules based on the temperature of the ai r . (8) Or, for the average velocity of a molecule: V= ✓ 8=T (9) For air near sea level (p = 101,320 Pa, T = 293 K) the average velocity of molecules in air is 463 m/s or 1,035 MPH. This value is just a little higher than the speed of sound in air (343 m/s or 767 MPH) as computed earlier. These molecules only travel a short distance before they collide with each other. This distance is defined as the "mean free path " given by the symbol A. (10) In this expression, d is the diameter of a molecul e, which is approximately 0.3 nanometers. For air at 20° C and 101,325 Pa, the mean free path (A) is approximately 100 nanometers or about 333 molecular diameters. When the supersonic projectile in Figure 4 moves through the air, molecules of nitrogen and oxygen in the air bounce off the vehicle's surface and collide with other molecules of air a short distance away. At the speed of sound, these molecules are not moving fast enough to get out of the way and a large number of molecules pil e up along a straight line that emanates from the nose or leading edge of the projectile as a "shock wave." Supersonic flow in the atmosphere labeled as region 1 passes through the shock and moves para llel to the surface of the body. The flow "expands" through a Prandtl-Meyer expansion fan at the end of the airfoil and speeds back up to its original Mach number. Flow in the boundary layer separates from the end of the airfoil and forms a highly turbulent wake downstream of the airfoil. The wake is also composed of Strouhal eddies that ca n subsist in the air long after the airfoil has passed by. The flow density, pressure, and temperature increases dramatically across the bow shockwave and returns to the original Mach number downstream of the airfoil. For a blunt-nosed object, as shown in Figure 5, the magnitude of the impact that the shockwave has on the flow is easier to explain. For a blunt object, the shock detaches from the surface of the object into the freestream in front of the object. Since the orig inal flow moving at M1 is traveling at 90° with respect to the shock near the nose of the object, the shock in this reg ion is referred to as a "normal" shock. The properties across a normal shock UNCLASSIFIED//FOR 0661El.t.L: W&&: OttLY 7
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Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 46 pages are in the text index: search them above, or from the library's search.