The design of efficient communication mechanisms for small satellite networks is a challenging task, requiring the definition and implementations of specific protocols and architectures appropriate to space's critical conditions. In this paper, we have proposed a specific nanosatellite mission and we have evaluated various nanosatellite constellations, using SaVi simulator, in order to identify the best constellation which satisfies mission requirements in terms of coverage and minimal number of nanosatellites. Next, XSTP (eXtended Satellite Transport Protocol) has been identified as candidate protocol for nanosatellite networks. Foremost, we implement XSTP in NS-2 simulator. The simulations were done for LEO traditional satellite network and nanosatellite constellation respectively. Finally, through analysis and simulations in NS2, we evaluated the performance of XSTP over traditional satellite networks and nanosatellite networks. Also, we were interested to compare XSTP performance to some TCP clones, in case of a high BER environment. The specific scenarios, implementations aspects and simulation approaches are presented in detail along with the respective results.