Inter-satellite calibration and cross-comparison of different instruments on different platforms provide a unique way to complement to the cal/val activities through independent verification. In this poster, preparation for NPOESS/NPP early on orbit inter-satellite calibration and cross-comparison are discussed. NPP, based on the assumed orbit, will over fly A-Train satellites; thus providing good opportunities to compare NPOESS/NPP SDRs and EDRs to those from well understood instruments, such as MODIS, AIRS, as well as experimental instruments, such as, CloudSat and CALIPSO. In this paper, we will discuss opportunities and frequencies for NPP instruments to match-up with A-Train instruments based on our simulations. We will also discuss the possibility to compare not only the nadir footprints, but also off nadir to some extend. SNO method (Simultaneous Nadir Overpass) will also be discussed. This method is very useful for inter-calibration and long term monitoring of instrument performance. We will discuss cross-comparison methodology and preliminary results with both current instruments on-orbit and simulated NPP data.