The Belgian User Support and Operations Centre (B.USOC) was responsible for the preparations and in-flight operations of the PCDF PROTEIN Mission that took place in ISS during four months in the first half of 2009. The Protein Crystallisation Diagnostics Facility (PCDF) allowed in-situ observation of nucleation and crystal growth behaviour of protein crystallisation experiments in microgravity. Therefore, incoming data could be analysed on-the-fly which permitted to modify the experiment in near-real-time. To achieve this experimental and operational flexibility, extensive preparation was needed. This paper reports on the various preparation and in-flight activities performed by the B.USOC operators and the PCDF science team that led to the successful PCDF PROTEIN Mission accomplishment.