This paper presents the planning concept that the Rosetta Science Operations Centre (RSOC) employs to coordinate the payload activities before arrival at the target comet 67P/Churyumov-Gerasimenko (C-G). The Deep Impact (DI) observations scenario is used as an example to illustrate the planning strategy. All the scenarios executed during the cruise to C-G have some characteristics in common that clearly distinguish them from the main mission at the target comet. The pre-comet scenarios have a limited duration of payload operations between several days and several weeks. They can be planned far ahead so that a duration of the planning cycle between 6 months and 1 year is acceptable. Results obtained during the execution of a pre-comet scenario usually do not feed back to updates of the remaining operations of the ongoing scenario, except very minor changes of e.g. measurement parameters. The planning concept defines the interfaces and schedules for the planning process involving the experiment teams, the Flight Control Team, the Flight Dynamics Team, and the RSOC. The following planning steps are identified: iteration of the top-level payload and spacecraft operations, iteration of the detailed operations with emphasis on pointing, iteration of the instrument timelines, lead time to execution, execution on the spacecraft, and reporting. The planning process is supported by software tools for manipulating command files, analyzing resources, checking constraints and analyzing the observation geometry.