Comparison of clinostat control strategies to achieve simulated microgravity with uniform gravity vector distribution

Experiments conducted onboard the International Space Station help investigate the physiological changes that living organisms undergo in microgravity. On Earth, the two-axis clinostat serves as an alternative that can continuously change the direction of gravity and simulate microgravity conditions by time-averaging the gravity vector. However, its structural characteristics inevitably produce poles where gravity is unevenly concentrated. This study conducted a quantitative analysis and comparison of pole formation across four representative clinostat control strategies. To evaluate the poles, two quantitative indicators were defined. The commonly used control strategies, maintaining a constant angular velocity or following a random distribution, were found to induce severe poles. In contrast, when the angular velocity of the external motor followed a specifically designed reciprocal sinusoidal profile, pole formation could be significantly reduced by adjusting the ratio between the minimum and maximum angular velocities. These trends, identified through simulations, were further validated through experiments using an inertial measurement unit.