DOW-UAP-D148: Detection and High-Resolution Tracking of Vehicles at Hypersonic Velocities

Source file: DOW-UAP-D148_AAWSAP-DIRD-Detection-and-High-Resolution-Tracking-of-Vehicles-at-Hypersonic-Velocities-November-20-2010.pdf Originating agency: Defense Intelligence Agency (DIA), Defense Warning Office, under the AAWSA Program Document type: Defense Intelligence Reference Document (DIRD), "Defense Futures" series; control number printed as "-08-1012-001" (the prefix is not visible on the scanned cover) Date: 20 November 2010 (information cutoff date, ICOD: 30 August 2010) Classification: UNCLASSIFIED//FOR OFFICIAL USE ONLY, with the FOUO caveat struck through on every page; publicly released in 2026 Page count: 46 VIRIN: 260918-D-D0360-1137 PURSUE Release: 6

Summary

This DIRD addresses a sensing problem rather than a vehicle: how to detect, and then track with high resolution, anything that crosses the atmosphere faster than about Mach 5. The cover carries the DIA seal, the "Defense Futures" banner, the date 20 November 2010 and an information cutoff date of 30 August 2010. The title page names the preparing office as the Technology Warning Division (DWO-4) of the Defense Warning Office, Directorate for Analysis, gives a single author, "AAP Person 83," and states that the paper is "one of a series of advanced technology reports produced in FY 2010" under the AAWSA Program, with comments to go to AAP Person 1, the AAWSA Program Manager.

The central idea is that a hypersonic object cannot pass quietly. It drives a bow shock ahead of it, heats and ionizes the air, glows, and leaves a turbulent wake that can persist long after it has gone; each of these effects is a potential signature. The paper surveys eight families of sensors that exploit them, rates them in a comparison matrix, and ends with four research recommendations for the next 30 years.

The paper does not mention UAP or UFOs. It is about meteors, reentry vehicles, missiles and aircraft, and its forward-looking chapter is aimed at foreign hypersonic aircraft and cruise missiles. Among the technical areas of the AAWSAP Statement of Objectives (DOW-UAP-D110) it serves signature reduction from the opposite direction, as a study of how signatures are exploited, together with the program's supporting topics.

Research Article

Structure and provenance

After an introduction, the 32-page body has four chapters: Theory Governing Objects in Flight, Hypersonic Compressible Flow Theory, Detection Technologies (electromagnetic, optical, and acoustic and seismic methods), and Vision of Progress Over the Next 30 Years. There are 19 figures and one table. An eight-page Appendix A reproduces a MathCad worksheet that computes conditions behind the bow shock of a vehicle flying at 3,300 mph at 10 km altitude (Mach 4.929, a post-shock temperature of 1,263 K and a peak emission wavelength of 2.295 microns), together with a U.S. Standard Atmosphere table up to 100 km. The 32 endnotes mix aerodynamics textbooks, journal papers, a 1961 Naval Research Laboratory report, conference papers and web pages accessed in July 2010, including amateur radio-astronomy sites. The released copy carries yellow highlighting on several passages, among them the definition of the hypersonic threshold (page 5), the four recommendation headings and values in the appendix.

The introduction sets the scale. The traditional hypersonic threshold is "about Mach 5 (1.7 km/sec)"; "low hypersonic" runs to about Mach 10, "high hypersonic" from Mach 10 to 30 or more. Four classes of object reach these speeds: meteors (up to 48 km/s, above Mach 150 in the upper atmosphere), reentry vehicles from low Earth orbit (8 km/s, above Mach 26.5), ICBM payloads (above 7 km/s, Mach 23 or more) and rockets and aircraft. The examples run from the X-15 and SR-71 to the X-51, the DARPA HTV-2, HyperSoar, Skylon, the Russian "Leninetz Ayaks" and "the alleged Aurora SR-91 (Mach 4 to 6)" (page 5).

The physics of a hypersonic signature

Chapter 1 is a compact aerodynamics lesson. It introduces the Mach and Reynolds numbers, the boundary layer and the eddies shed into the wake, whose frequency is described by the Strouhal number; "By measuring the Strauhal frequency, the velocity of the projectile can be determined with moderate accuracy" (page 9). Table 1 (page 13) works through a normal shock at Mach 3 at sea level: the flow behind the shock drops to Mach 0.475, pressure rises by a factor of 10.333 and temperature from 20°C to 512°C.

Chapter 2 explains why the textbook equations fail at higher speeds. The Rankine-Hugoniot relations predict 29,787°C near the nose of a blunt body at the reentry speed of Mach 26.5, "while the actual temperature only reaches 7,600° C," because energy is absorbed in ionizing and dissociating the air (page 14). That ionization produces the glowing trail behind meteors and reentry vehicles and interferes with radio, but "provides a convenient way to identify hypersonic objects." The paper's working "rule of thumb" is that peak shock-layer temperature in kelvin is about 1,000 times the speed in km/s, so a reentry vehicle at 8 km/s reaches about 8,000 K.

Radar and passive radio

Chapter 3 opens with a taxonomy (Figure 7) and a laboratory benchmark, the laser chronograph, which times an object between two beams to a fraction of a nanosecond but works only if the object flies through the beams on an instrumented range. The paper then states its main judgement: "Currently, the best devices for the detection of hypersonic vehicles are based on the reflection of radio and microwave radiation through RADAR and upon the detection of infrared energy emitted by the ionized gases surrounding high-speed vehicles and in their wake" (page 16).

The radar section covers the physics (the radar equation, under which "energy received in reflected energy decreases by 94% every time the distance to the target is doubled"), Doppler velocity measurement and stealth, then lists real systems (page 19): a Naval Research Laboratory over-the-horizon radar at the Chesapeake Bay Annex that tracked a Mercury/Atlas launch on 9 September 1961; Cobra Dane in Alaska and the ship-borne Cobra Judy, used against reentry vehicles above 35 km; the early-warning radars in Alaska, Great Britain and Greenland; a 100-kW millimetre-wave radar on Kwajalein Atoll that tracks reentry vehicles out to 2,500 km; and TRADEX, built in 1963, tracking at up to 1,400 km. The summary adds that AWACS can see objects at up to 370 km with 0.5-metre resolution and that TRADEX can follow six objects at 1,400 km with 3-metre accuracy and a velocity resolution of 0.01 m/s (page 35).

The most original idea in this part is passive "radio reflection detection" (pages 19-20, Figure 11). A receiver over the horizon from a radio or television transmitter normally hears only hiss; when a meteor's ionized shock and wake pass between them, it hears "pings and whistles." Citing hobbyist recordings of the 2007 Aurigid meteor shower at 61 and 217 MHz, the author says shock and wake reflections can be told apart, that a network of such receivers could triangulate a hypersonic object, and that the wake "whistles" might reveal the eddy frequency and hence the speed. The paper concedes the technique "is not fully developed and appears to be employed only by hobbyists," and concludes that it "should be further developed" (page 20).

Cameras, satellites and infrared

Optical methods start with meteor science: all-sky cameras, the 1959 Příbram meteorite, the Neuschwanstein meteorite recovered with the help of the European Fireball Network (stations about 100 km apart covering about 1,000,000 km²), and asteroid 2008 TC3, which entered over Sudan on 7 October 2008 and yielded 280 fragments weighing 11 pounds (pages 20-21). The author's point is that the same camera networks could follow any hypersonic aircraft whose wake glows, though only at night. Reconnaissance satellites are listed with orbits and resolutions: KH-11 (2-3 metres), "Big-Bird," "Close-Look" and Landsat.

Infrared gets the longest treatment. Using the Stefan-Boltzmann, Planck and Wien laws, the author computes that a sphere at Mach 3 at 10 km altitude heats the shocked air to 597 K, with peak emission at 4.85 microns, shifting to 3.92 microns at Mach 3.5, a difference detectable by "an infrared camera or FLIR" (page 24). Satellite sensors watching the 2.5-5 micron band "could detect aircraft with speeds as low as Mach 3" (page 25); a real missile must be confirmed in both the 2.6-3.2 micron water-vapour band and the 4.1-4.8 micron band to reject clutter and sunlight "glint." A historical section (page 27) traces satellite infrared warning from RAND's 1955 study and the WS-117L "ICBM Attack Alarm System" through MIDAS (MIDAS 9 detected nine launches in 1963) to the Defense Support Program, whose satellites carry 6,000 infrared detectors working at 2.7-4.3 microns and whose 23rd and last satellite was launched in November 2007. DSP detected a large meteor over the western states in 1972 and 88 Iraqi SCUD launches in 1991; "The current operational inventory is classified."

LIDAR, infrasound and seismic networks

LIDAR is presented as the tool for the wake itself. Pulsed lasers with Raman and scattering analysis can measure particle density, gas species, temperature and air velocity along the beam, so "LIDAR can also detect the presence of a hypersonic vehicle by measuring the air velocities in the long turbulent wakes that they leave in the atmosphere" (page 29). The precedent offered is a U.S. Army LIDAR that measured nose-cone erosion products from Athena-H reentry missions at White Sands Missile Range in 1973, at 9.3 and 14.3 km altitude.

Acoustic methods exploit the Mach cone. Two microphones make a chronograph; the Mach angle gives altitude. The paper recounts the Air Force's 1960s infrasound network for nuclear-test detection, four Los Alamos stations installed in 1983 that tracked large bolides in 2000 and 2001 (one exploding near Baja California with the energy of 6,000 tons of TNT), and the 321-station International Monitoring System, whose value for nuclear monitoring it calls "dubious" because in November 1999 it could not tell a meteor from a nuclear explosion over northern Germany (page 30). Seismometers also register sonic booms: Southern California's 200-station TERRAscope network recorded an SR-71 at Mach 3.2 over Edwards Air Force Base on 9 December 1993 and the reentry of the shuttle Discovery (STS-42) on 30 January 1992, and 66 stations in Washington and Oregon followed another Discovery landing for 500 km, fixing its speed at Mach 14 at 55 km altitude. The one "mystery" in the paper belongs here: booms heard over Southern California in 1991 and 1992 were traced, with TERRAscope data, "to two F-4 Phantom aircraft flying over Edwards Air Force Base at speeds near Mach 1" (page 31).

Thirty years ahead: four recommendations

Chapter 4 sorts future targets into space debris, reentry craft (the Apollo 10 capsule's 24,790 mph is cited as the manmade speed record), meteors, missiles and hypersonic aircraft, then turns to vehicles "capable of Mach 8 and above." Its four recommendations (pages 33-35):

1. Build a database of wake characteristics for existing aircraft. Citing University of Dayton researchers Mark Garnet and Aaron Altman, who identified F-15, F-16, F-18 and B-52 wakes, the paper notes that "although the aircraft may be designed for stealth, their wakes cannot be hidden." A hydrogen-fuelled vehicle would even betray itself by the absence of carbon in its wake.
2. Exploit the features that let hypersonic aircraft fly. Pulsed detonation engines leave periodic bulges described as "donuts on a rope"; the Russian AYAKS design, which uses lasers and RF generators to ionize the air ahead of it and an MHD engine, would emit RF, laser and electromagnetic signals. "Every new propulsion or drag reduction system under development will have some characteristic that may make it more detectable."
3. Explore the detection of vehicles "designed to be undetectable." The paper quotes a 1999 paper on the AJAX project claiming that a plasma film could make a missile impervious to radar, "thereby rendering it electronically 'invisible'," and answers that its carbon-rich wake and hotter skin should remain visible to LIDAR and infrared.
4. Develop novel detectors: ultraviolet and X-ray telescopes for recombination radiation, LIDAR for nitrogen oxides in wakes, and sensors for the "significant positive charge" a hypersonic object acquires.

Figure 19 (page 36) scores each method on what it measures, sky coverage, availability and cost. Radar measures distance, velocity and altitude at "Modest" cost; passive radio reflection is "Low" cost but marked only for meteors and reentry vehicles; the chronograph measures velocity only and is not marked useful against any class of target.

A few slips should be noted. The paper gives UHF radar as "300 to 1,000 GHz" (page 17) and gas-gun speeds as "12 km/h" (page 15), where the context requires MHz and km/s, and it dates the same X-15 speed of 7,274 km/h (4,520 mph) to 1964 in the introduction and to 1967 in Chapter 4.

Significance

D148 is one of the most practically oriented DIRDs in the AAWSAP series. Where many of its siblings examine exotic propulsion, this paper asks the counterpart question: how would one detect and track an object moving at extreme speed through the atmosphere? Its answer is layered and multi-sensor. Radar and infrared lead, wake-based methods (LIDAR, passive radio, infrasound and seismic arrays) help identify the vehicle, and the author argues repeatedly that any new propulsion or drag-reduction trick creates a new signature. The treatment of the Ayaks concept links it directly to the next paper in the series, DOW-UAP-D149, dated one day later, which examines MHD propulsion and the Ajax bypass idea in depth.

Readers interested in UAP will recognise the sensor families it discusses, from infrared early-warning satellites to infrasound and seismic networks, but the paper draws no connection to unidentified phenomena. Its only brushes with the unexplained are the "alleged" Aurora aircraft and the Southern California booms, which it reports as solved. Its recommendations are framed around foreign hypersonic aircraft and cruise missiles, and its evidence comes from open literature, including hobbyist websites, rather than from intelligence reporting.

Key People

Locations

Key Concepts

Notable Quotes

"Currently, the best devices for the detection of hypersonic vehicles are based on the reflection of radio and microwave radiation through RADAR and upon the detection of infrared energy emitted by the ionized gases surrounding high-speed vehicles and in their wake." -- page 16

"This means that energy received in reflected energy decreases by 94% every time the distance to the target is doubled." -- page 18

"This technique for detecting hypersonic meteors is not fully developed and appears to be employed only by hobbyists." -- page 20

"The energy difference between a Mach 3 and Mach 3.5 aircraft would be significant enough to detect with an infrared camera or FLIR (forward looking infrared) detector." -- page 24

"By using data from the TERRAscope array, the source of these disturbances was traced to two F-4 Phantom aircraft flying over Edwards Air Force Base at speeds near Mach 1." -- page 31

"They point out that, although the aircraft may be designed for stealth, their wakes cannot be hidden." -- page 33

"Every new propulsion or drag reduction system under development will have some characteristic that may make it more detectable from the ground or from satellite." -- page 34

"As hypersonic objects pass through the atmosphere, the object becomes ionized with a significant positive charge. Technology should be developed to sense the flight of objects with an electrostatic charge as they pass through the atmosphere." -- page 35