Rheometry serves as a method for the determination of effective length vectors of short antennas by means of electrolytic tank measurements. This paper reports on the application of rheometry to the three linear monopoles mounted for the purposes of the Radio and Plasma Wave Science Experiment on the Cassini spacecraft, which will fly to planet Saturn. The voltage signals induced by incoming waves from the Saturnian radio emissions will be recorded for further evaluation. By direction-finding techniques one will trace back from the collected data to the source regions of the received radio waves and determine the wave polarization. An accurate direction finding is only possible if the effective length vectors of the antennas, which are affected by the spacecraft body, are known to a certain degree of accuracy. It is investigated how rheometry enables the determination of the effective length vectors with the help of a scale model. After a detailed discussion of the fundamentals of rheometry, the application of rheometry to the Cassini scale model is described. The results of the measurements are graphically depicted and discussed with the requirements for direction finding taken into consideration. Finally, an overview of the inflight antenna calibration is given, which will be possible by utilizing the strong Jovian radio emissions during Cassini's Jupiter flyby.