“If your estimate of the velocity is off, then [the object] is moving faster or slower than you think, so over time it ends up moving more or less than you think,” says Sedwick. At an orbital velocity of, say, 7,500 meters per second, an error of only a few centimeters per second might sound low, but it will cascade over time. After just a single day, the object could be several kilometers away from where you would expect it to be. Compounding this process are factors like atmospheric drag and object orientation. And not all objects are measured every single day. As a result, you can hardly ever know the exact whereabouts of an object at a given moment—you have to rely on broad estimations.