The primary object of the TanDEM-X mission is to generate a highly accurate digital elevation model (DEM) with never achieved accuracy on global scale . But in addition to this DEM acquisition realized by a helix constellation of two satellites, nominal TerraSAR-X operation shall be available anymore, i.e. the bistatic TanDEM-X mission and the monostatic TerraSAR-X mission have to be operated in parallel with both satellites. Consequently the second satellite TDX, scheduled for launch in the first half of 2010, has to achieve the same accuracy and performance as those of the first satellite TSX, already in-flight since 2007. For this purpose a defined number of acquisitions over precise reference targets deployed within the DLR Calibration Field in Southern Germany and across the DLR test area in the Amazon Rainforest will be executed. Consequently, SAR instrument calibration is the main driver for the duration of the commissioning phase. But, the TanDEM-X commissioning phase has to be performed as fast as possible, because only then a maximal overlap of the lifetime of both satellites can be ensured. Hence, an efficient calibration strategy will be applied based on innovative and exact calibration techniques and successfully demonstrated with TSX .