Kepler planned to test his theory from Mysterium Cosmographicum based on the Mars data .
Kepler estimated that the work would take up to two years ( since Kepler was not allowed to simply copy the data for Kepler 's own use ) .
Kepler planned to test his theory from Mysterium Cosmographicum based on the Mars data , but he estimated that the work would take up to two years ( since he was not allowed to simply copy the data for his own use ) .