Computes the total debris flux of all particulates. The debris model is valid only for near-circular orbits at altitudes between roughly 300 km and 2250 km. Because the model was created using averages over long time periods (e.g., many months or a few years), it is not appropriate to output a flux value at any given time - there really is no information in different evaluations of the model over short time spans. Hence, the debris flux is evaluated at just 1 sample per requested time interval, at the midpoint of the interval. Valid for vehicles whose central body is earth.