What is a “debris footprint?”
Debris that survives reentry will impact within a “debris” or “impact” footprint, the area on the ground which contains all of the debris pieces. It is possible to estimate the size of the footprint, but very difficult to predict where the footprint will be on Earth’s surface or where specific pieces of debris will land.
The size of the footprint is determined by estimating the breakup altitude of the satellite or space hardware and then estimating the mass and aerodynamic properties of surviving debris. The heavy debris will generally travel farther downrange to the toe of the footprint; lighter material will generally be near the heel. Footprint lengths can vary from 185 km to perhaps 2,000 km, depending on the characteristics and complexity of the object.
The footprint width is generally determined by the effects of wind on the falling debris objects, with heavy objects affected less, and lightest the most. The width of the footprint may also be affected by the breakup process itself. For example, if the object should explode during reentry, fragments will be spread out across the footprint. A footprint width of perhaps 20-40 km is typical, with the most pronounced effects near the heel of the footprint.
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