Analysis of artificial gravity paradigms using a mathematical model of spatial orientation

Artificial gravity (AG) is a promising approach to reduce the physiological deconditioning experienced by astronauts. Here we propose the linear sled hybrid AG system as an alternative to the typical centrifuge approach to creating AG. In this paradigm, the rider is briefly linearly accelerated towards their head, then rotated 180 around, then decelerated. This sequence is repeated creating footward loading during the linear acceleration and deceleration phases, replicating standing upright on Earth, without any gravity gradient or Coriolis forces. The 180 rotation also produces gradient centripetal acceleration, for a "hybrid" approach. We simulated the well validated observer model to predict the rider's orientation perception and potential disorientation in response to these two AG paradigms. Particularly, we simulated head tilts to investigate the cross-coupled illusion. For the centrifuge, as expected, we found head tilts caused the cross-coupled illusion and an illusory sense of tilt. As a novel prediction, we found the head tilt angle and centrifuge spin rate to interact non-linearly, producing an inflection point in the peak perceived tilt of the cross-coupled illusion. We found the linear sled paradigm to be well perceived and, as expected, head tilts did not produce the cross-coupled illusion. While the observer model predicted the linear sled paradigm to not be disorienting, future experimental work is necessary for validation. Comfort and motion sickness feasibility, as well as countermeasure efficacy, should be studied experimentally.