ballistic limit—either the combination of geometry and material properties of a target (such as a debris shield) that is necessary to prevent a given impacting particle from perforating it at a specified velocity, or the minimum size of a particle that perforates a given target at a specified velocity, or the velocity beyond which a given particle will perforate a given target.

ballistic limit equation (BLE)—equation defining a curve (often referred to as a ballistic limit curve, or BLC) that is typically plotted in projectile diameter-impact velocity space and is a line of demarcation between those diameter-velocity combinations that result in target perforation and those combinations that do not.

breakup—destructive fragmentation of a space object. Breakups may be either accidental or intentional.

BUMPER—a NASA semi-empirical computer code that calculates the probability of system failure (e.g., spacecraft wall penetration) in light of specific design features.

cataloging—process of detecting, identifying, and determining the discrete orbit of a space object.

characteristic length—the arithmetic mean of the three major mutually perpendicular dimensions of an object.

cis-martian region—the region of space between the orbit of Earth and Mars.

confidence interval—the probability that the true number lies in a set of values.

conjunction—the point of closest approach of two objects.

conjunction (assessment risk) analysis—the process performed for mitigating the risk of an operational satellite colliding with a cataloged object. Known as Conjunction Assessment Risk Analysis (CARA) at NASA/GSFC for robotic spacecraft and conjunction analysis (CA) at JSC for the International Space Station and future U.S. human spacecraft operations.

cross-tagged—indicating a situation in which the observations for two (or more) closely separated objects are associated with the tracks of the other object(s).

damage predictor equation (DPE)—an equation that predicts damage (e.g., hole diameter, crater depth) to system components in terms of an impacting particle’s density, velocity, and angle of impact and the geometric and material properties of the target.

debris—see “orbital debris.”

Debris Assessment Software (DAS)—suite of tools (ORDEM, orbit propagators, and ballistic limit equations) that produces a first-order assessment of the risk of human casualty associated with uncontrolled space vehicle reentries.

decay—natural loss of altitude of a space object, culminating in reentry into Earth’s atmosphere.

deorbit—deliberate, forced reentry of a space object into Earth’s atmosphere by applying a retarding force, usually via a propulsion system.

destructive scattering—for electromagnetic waves that interact, the interference that produces a net decrease in the amplitude of the resultant waves.

electromagnetic pulse (EMP)—a short but intense burst of electromagnetic energy.

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