In this work we aim to address the challenges of fusing motion parameters measured using different sensing modalities, as temporal resolutions differ widely between navigator and external motion tracking techniques. A model is presented in which head motion is characterised as simple rolling motion. The resulting equations describe subject motion to within 2 mm when applied in an open loop manner. A filter, with feedback, is then implemented where navigator data is used to estimate model parameters. The filtered translation output is smooth without the cost of increased latency due to the fast orientation estimates.