ESRIN—The European Space Agency’s Centre for Earth Observation, located in Frascati, Italy.

flyby trajectory—A spacecraft’s flight path designed to pass in close proximity to an object but not go into orbit around or impact the object.

gamma ray—Very high energy electromagnetic radiation.

George E. Brown, Jr. Near-Earth Object Survey Act of 2005—A congressional act mandating the discovery by 2020 of 90 percent of cosmic objects 140 meters in diameter or greater.

Goldstone Solar System Radar—Located in the Mojave Desert in southern California, a steerable 70-meter-diameter antenna that transmits and receives radio waves. It is part of NASA’s Deep Space Network and is operated by the Jet Propulsion Laboratory under contract with NASA.

gravity assist—Using the gravity of a planet to change the path and/or speed of a spacecraft.

GTO—Geostationary Transfer Orbit, an intermediate orbit used to move a spacecraft from low-Earth orbit to a geostationary orbit where the spacecraft remains stable above a particular point on Earth’s equator.

Hayabusa—A Japanese spacecraft mission that rendezvoused with the subkilometer NEO Itokawa in September 2005.

heliocentric orbit—An orbit around the Sun.

heliocentric velocity—The velocity of a body relative to the Sun.

Human Space Flight Review Committee—Commissioned by President Obama in May 2009 to review current U.S. human spaceflight plans and programs. The committee concluded its review in September 2009. Also konwn as the “Augustine Committee.”

hydrodynamic simulation—A computer model created to simulate the behavior of fluids in motion.

hyperbolic approach—One orbiting body approaching another along a hyperbolic trajectory.

IAU—International Astronomical Union, the international professional society for astronomers; provides guidance for the Minor Planet Center.

imminent impactor—A space object of natural origin whose impact with Earth is imminent.

impact energy—The amount of energy delivered by one body in an impact with another. Units are often given in megatons (MT), which refers to a comparison with the chemical energy release of a million tons of TNT. Also known as kinetic yield.

impactor—A physical object that collides with a target object at a high velocity, transferring momentum (and energy) to alter the target object’s orbit. Also called a kinetic impactor.

inclination—In this report, the angle between the plane of an orbit and the ecliptic (the plane containing Earth’s orbital path).

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