The Satellite Path
The path to be followed by satellite (dotted line) does not change due to the fact that the satellite is falling and can be used to assess the trajectory of the object before and after possible fall. In the graph, each point marks the range of 1 minute.
Solar Flux and Other Variables
As much as the institutes and space agencies strive to provide correct data of the point where the space debris will fall, several factors may interfere with the accuracy of the prediction. Among the most important, the solar flux is the most critical because it determines the conditions of the upper atmosphere, increasing or decreasing the drag on the object.
Besides the solar flux acting on the aerodynamic characteristics, another variable rather difficult to be computed is the resistance of materials used in the construction of the object and the shape of the structure. Combined, these factors may determine different altitudes for the moment of rupture, causing errors of more than 30 km in altitude reentry provided.
Other variables that affect the calculation of reentry, although less important, are the gravitational perturbations of the Sun and Moon and also those exercised by large mountain ranges, above or below sea level.
The modeling used by Satview to compute the time of reentry uses solar flux data obtained at the time of modeling, and prediction of the behavior of the sun for the next 5 days. With this, the margin of error of prediction is + / - 3 revolutions for satellites or debris in uncontrolled reentry.
Altitude of Reentry
Spacecraft reentering the atmosphere without control usually break between 72 and 84 km altitude due to temperature and aerodynamic forces acting on the structure.
The nominal breakup altitude is 78 km, but big satellites that have larger and denser structures survive longer and break down at lower altitudes. Usually, solar panels are destroyed before any component, at altitudes between 90 and 95 km.