Spacecraft jitter prediction using 6-DOF disturbance measurements

Recent trends in spacecraft development favor optical payloads with good resolution on low mass platforms with agile pointing capability. For a payload with good resolution, pointing stability is a key performance metric. However, as spacecraft inertia decreases, the payload line-of-sight stability becomes increasingly susceptible to disturbance inputs. In addition, as spacecraft agility increases there is a corresponding increase in disturbances from attitude control actuators. SpaceDev has developed a 6-DOF measurement platform, known as the hexapod reaction balance, to accurately measure disturbance inputs from attitude actuators. It is based on 6 force transducers that are mapped to force and moment measurements at 10 kHz. In addition, we have created a technique for reducing the data in the frequency domain and applying it to spacecraft structural models to predict system jitter. This paper discusses the system wide issues of creating a jitter prediction in the context of the SpaceDev Trailblazer satellite, which includes 4 reaction wheels as disturbance inputs and a finite element model of the structure. Data collection, data reduction, system modeling, and typical results are presented.