characterization—The determining of various characteristics of a celestial object, including but not limited to orbit, rotation, size, composition, and albedo.

chemical energy—The energy released in a chemical reaction, measured here in terms of the energy released when TNT (trinitrotoluene) is detonated.

Chicxulub Crater—An approximately 200-kilometer-diameter impact crater formed 65 million years ago in the Yucatan Peninsula and associated with the extinction of the dinosaurs.

civil defense—A mitigation option, civil defense entails protecting the population by taking precautions on the ground, such as advanced warning, evacuations, and the provision of protective shelter. It is already used for natural disasters such as hurricanes.

contact forces—A force exerted through physical contact with an object.

CSS—Catalina Sky Survey, a system of three telescopes located at the Mount Lemmon Observatory in Arizona, the Mount Bigelow Observatory in Arizona, and the Siding Spring Observatory in Australia (funded by NASA). CSS currently discovers NEOs at the highest rate of any operational telescope system.

CSS+—Catalina Sky Survey Binocular Telescopes, a proposed series of three binocular telescopes fully dedicated to discovering NEOs, based on using six existing 1.8-meter-diameter primary telescope mirrors. CSS+ is currently not funded.

ΔV“Delta-V”: Change in velocity.

Deep Impact—A NASA mission during which a spacecraft collided with comet Tempel-1 in July 2006; an example of a kinetic impact (see impactor).

Deep Space Network—A network of three deep-space communications facilities placed approximately 120 degrees apart around the world that supports interplanetary spacecraft missions and radio astronomy observations as well as selected Earth-orbiting missions. Facilities are located at Goldstone in California’s Mojave Desert; near Madrid, Spain; and near Canberra, Australia.

Discovery Channel Telescope (DCT)—A telescope with a 4.2-meter-diameter mirror under construction in Arizona. A collaborative effort between Lowell Observatory and Discovery Communications, the telescope is designed to contribute to multiple astronomical projects, including searches for NEOs. Its approximately $14 million camera is not yet funded.

dissipative surface—In the context of this report, a low-density, porous surface (e.g., of an asteroid) on which the energy from an impact or explosion is dissipated across the surface rather than transferring to the interior of the body.

Don Quijote—European Space Agency mission that is not funded. The proposed mission involved an NEO impactor and an observation spacecraft.

Eccentricity (e)—A measure of how much an orbit’s shape deviates from a circle. For circular orbits, e = 0. As e becomes greater, the orbit’s shape becomes increasingly elongated.

electric propulsion—A method of spacecraft propulsion using charged ions for thrust.

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