Does a mathematical expression exist that puts the duration of a satellite in terrestrial orbit as a function of both major and minor axis, solar activity (measured in mean sunspot numbers, perhaps), global density of the satellite (to account for extreme cases such as the Echo balloons)...? If there isn't, I would like to derive an approximate interpolation polynomial of several variables; at least four, but perhaps as much as six or seven. In that case, I would need a database of decayed satellites and thus build the polynomial. Please advise Regards and thanks in advance Javier Susaeta <javier.susaeta@nexo.es>