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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/fFOR. QFFIEl.t.L: Uii QD:I! X Chapter 2: Hypersonic Compressible Flow Theory Hypersonic flow is typically assumed to apply to objects traveling at M > 5. Figure 6 shows that, for Mach numbers above 5, the ratio of Mach numbers across the shock approaches a constant va lue of 0.378, although temperature and pressure ratios contin ue to increase. In hypersonic flow, the bow shock, or Mach angle, /3, approaches the half-angle, 0, of slender airfoils and the drag coefficient reaches a constant value that does not change with Mach number. The drag coefficient actually becomes a simple function of the half-angle of the airfoil, and the boundary layer is squeezed between the shockwave and the airfoil surface. 150 •I • - ' - -~..-+---+----+-----ie-----+---+----+----+--'---l- ' - .. • ..... - ·-- .. , ·-···-·•--1111--- .. .. • •• • • "' • • • • • • • • • .- - :::::::::l:±::t::c J- - OL J d 09 0.8 0.7100 06 T nllio( M ) 0.5 M z( M ) P,mio( M ) ... 0.4 50 03 0.2 .-~-. -;;;-·· -~· --~----~· -··· ·-,~· o.JI 2 3 4 5 6 7 9 1S M Figure 6. Ratios of Mach Number, Temperature, and Pressure Across a Normal Shock In hyperson ic flow, the Rankine-Hugoniot equations, which are based on the perfect gas law (p = pRT), fail to predict the real behavior of air at extremely high temperatures. Equation 12, for example, predicts a temperature of 29, 787° C in the air near the surface of a blunt obj ect traveling at the reentry Mach number of 26.5, wh ile the actual temperature on ly reaches 7,600° C. The reason for this discrepancy is due to ionization of molecu les of air as electrons are stripped away by the high temperatures tha t exist across the shock. Some energy is used to produce this ionization, and above temperatures of 550° C, equation 15 does not accurately predict air temperatures due to shocks. Ionization is responsible for the glowing wake that follows reentry vehicles and meteors as electrons rush to recombine with ions releasing x-rays and visible light. The ionization also interferes with radio transmissions, but provides a convenient way to identify hypersonic objects due to the emitted light. A "rule of thumb" is that the peak shock layer temperature in degrees kelvin is 1,000 times larger than the aircraft speed in km/s. By this standard, a reentry veh icle at 8 km/s (Mach 26.5) would have a maximum shock layer temperature of 8,000 K. At temperatures above 2,000 K, nitrogen and oxygen gas in the form of 02 and N2 will disassociate into individual ions, consuming more energy from the flow. UNCLASSIFIED//EQA: QlililEl.t.L: W&&: O,.L'l 10
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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.