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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.
“Anderson”2 pages
UNCLASSIFIED/fFOR. QFFIEl.t.L: Uii QD:I! X Introduction An object is supersonic when its speed through the atmosphere is greater than the local speed of sound . The Mach number is defined as the speed of the object divided by the local speed of sound . For Mach numbers greater than 1 (supersonic flow), shock waves develop in the flowfield and near the surface of the object due to the air's compressibility. Traditionally, the lower Mach number limit for the so-called hypersonic speed regime is about Mach 5 (1. 7 km/sec). "Low hypersonic" values range between Mach 5 to about Mach 10, while "high hypersonic" values range between approximately Mach 10 to Mach 30 or above. Mach 30 (10 km/s), for example, is close to Space Shuttle reentry velocity . Few objects can travel at hypersonic velocities. The most common object that we see movin g at these speeds are meteors entering the Earth's atmosphere. As meteors fall to the Earth's surface, their velocities may reach 30 miles per second (48 km/s), 1 and their corresponding Mach number as they enter the upper layers of the atmosphere will exceed 150. Meteors are preceded by a bow shockwave as they compress the air immediately in their path. Temperatures and pressures increase dramatically across the shockwave to a point where the gases in air ionize and disassociate, leading to the emission of visible light and radio waves. These conditions also lead to rapid heating of the meteor surface causing them to fracture and break up as they enter the atmosphere. Optical and RADAR-based surveillance systems are now used to scan outer space to detect asteroids and other objects with orbits that may lead them to collide with Earth. A second class of hypersonic objects includes reentry vehicles moving into the Earth's atmosphere from orbit. In the case of a reentry vehicle returning from low-Earth orbit at 100 km altitude, the velocity of the vehicle will reach 8 km/s (about 5 miles per second). The Mach number of this vehicle will exceed 26 .5 in the upper atmosphere. As the vehicle moves through the atmosphere, flow-induced drag forces will slow down the vehicle; if the vehicle has sufficient thermal protection, it can survive reentry and be recovered. A third class of hypersonic vehicles includes the reentry payload used in ICBMs (intercontinental ballistic missiles). The payload in these missiles is launched using a rocket that boosts them above the atmosphere to a suborbital velocity. The payload velocity may exceed 7 km/s as they reenter the atmosphere, equating to M > 23. The coupled high velocity and high kinetic energy of these objects creates an ionized wake and shock wave that can be used to detect their position and to determine their velocity. This information, along with their ballistic trajectory, is used to locate their target and the time to impact. A fourth class of hypersonic vehicles includes manned and unmanned rockets and aircraft. The North American X-15, for example, exceeded a speed of 7,274 km/hr in 1964, equating to about M = 6.5. This aircraft also exceeded 100 km in altitude on two occasions, qualifying the X-15 as a spacecraft. The SR-71 Blackbird, an air-breathing strategic reconnaissance aircraft, has exceeded Mach 3.2 at 80,000-ft altitude, and its actual maximum speed may have reached into the hypersonic flow regime. Other real and conceptual aircraft capable of reaching hypersonic speeds include the alleged Aurora SR-91 (Mach 4 to 6), the Boeing X- 51, an unmanned Mach 6 scramjet, the HTV-2 from the DARPA Falcon project (designed for M=20 flight to low-Earth orbit), the HyperSoar (M = 12), the Russian Leninetz Ayaks, and the Skylon (designed for single-stage-to-orbit flights). Certain rockets are also designed to travel at hypersonic speeds. The Patriot missile, for example, travels at Mach 5, a high speed necessary for it to be able to intercept and destroy other missiles while they are in flight. UNCLASSIFIED//EQA: QlililEl.t.L: W&&: O,.L'l 1
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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.