Satellite networks have the potentiality to guarantee ubiquitous access to the Internet. Yet, their transmission delay and errors represent still a challenge for researchers and practitioners, especially when considering TCP-based flows. Having efficient means to estimate important channel channel features such as, for instance, the available bandwidth and the total capacity has been proven to be proficient in improving the performance in this context. To this aim we discuss SBE (shareable bandwidth estimator), a solution able to provide a simple and effective estimation of the bottleneck link capacity minus the simultaneously present uniformly distributed traffic. Simulative experiments prove that our scheme is effective since the very beginning of a connection. Furthermore, SBE can be easily implemented as it requires only sender-side modifications and is based on regular TCP functioning.