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This Defense Intelligence Reference Document, dated 2 March 2010, was prepared by the Defense Intelligence Agency's Defense Warning Office under the Advanced Aerospace Weapon System Applications program. It reviews invisibility through camouflage, transparency, and cloaking, covering metamaterials, transformation optics, and non-Euclidean broadband cloaking designs. It concludes that perfect cloaking is impossible, but imperfect devices could be made. Microwave cloaking is within reach of present technology, while visible-light invisibility remains uncertain and depends mainly on new theoretical research.
From the source:Release of 2026-09-18 Incident: 3/2/10, 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 the theory and early experiments behind invisibility cloaking, describing several ways an object might be hidden from visual or sensor detection, including camouflage, transparency effects, and optical cloaking that bends light around an object. It focuses mainly on metamaterials, negative refraction, and transformation optics, and reviews experiments that had already demonstrated limited cloaking at microwave frequencies. The report argues that “imperfect” cloaking is physically achievable in some parts of the electromagnetic spectrum, especially for microwaves, but that “perfect” cloaking is not practical because it would require material properties that conflict with the underlying physics. Its overall conclusion is that cloaking is a scientific field with plausible narrow applications, but that useful visible-light cloaking depends more on future theoretical breakthroughs than on conventional advances in materials science.
UNCLASSIFIED/ /POK OFFICIAL USE Oilti dimensional plane, one can use the stereographic projection, the central ingredient of the Mercator projection in cartography that is used to map the surface of a round object, the Earth, onto a flat sheet of paper. A line drawn from the North Pole of the sphere through a point on the surface intersects the equatorial plane at one point. This point is the stereographic projection of the point on the sphere. Figure 19 shows that the stereographic projection of a circle on the sphere is a circle on the plane with a different radius. The stereographic projection distorts the measure of space, but the distortion around any given point is the same in all directions, because otherwise circles would be deformed. Therefore, an optical material that implements the geometry of the sphere via the stereographic projection must be isotropic. One can read off the required refractive index from the drawing as follows: in virtual space, on the sphere, light propagates at the speed of light in vacuum from a point to its infinitesimally close neighbor; in physical space the distance between the two infinitesimal neighbors is modified-the speed of light is changed by the refractive index that is given by the ratio between infinitesimal distances in virtual space and the corresponding distances in physical space. For the stereographic projection, the refractive index is smaller than 1 for points on the northern hemisphere and larger than 1 on the southern hemisphere. This device is known as Maxwell's fish eye lens. 33 In this lens, light follows the great circles, light goes around in circles, and light rays meet at antipodal points; the fish-eye makes a perfect lens (although a fairly near-sighted one). It is possible to extend these ideas to three-dimensional curved spaces. For example, the surface of the four-dimensional sphere is a three-dimensional curved space, and the device implementing this hyperspace object is just a three dimensional fish-eye. Hyperspace is not out of this world; it can be built, and it turns out to be practically useful for invisibility. 34 Figure 19. Stereographic Projection UNCLASSIFIED/ /FOR 8ffl@IAI:: 1:JSi 8PtLY 18
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Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 29 pages are in the text index: search them above, or from the library's search.