Abstract. This paper discusses the schedulability analysis of a PulseWidth Modulation (PWM) control algorithm of an on-board spacecraft software system. The UPMSat-2 case study is used to discuss the scheduling approach of the task set of the Attitude Determination and Control System (ADCS). The Ravenscar profile is a key element of the project in order to ensure temporal predictatibilty and analysability. However, the task population must be maintained low as available computational resources are limited. As a result, the PWM task has not a single activation point, which prevents a traditional schedulability analysis. The approach used by the authors to carry out the scheduling analysis is presented in the paper.