LAUSR

Abstract The random positioning machine (RPM), which continuously changes the gravity direction acting on a subject, can provide the simulated microgravity and planet hypogravity environments to the bioreactor on Earth. In this study, a theoretical analysis of the microgravity and planet hypogravity fields generated by the RPM motion was attempted. The simulated microgravity fields around the subject were quantitatively analyzed by the newly defined degree of gravity dispersion (DGD) parameter, and the simulated planet hypogravity fields were analyzed by the gravity ratio between the RPM simulation and a real planet, corresponding to the normalized DGD. The motion of the gravity vector tip (GVT) on an imaginary sphere attached to a rotational subject was traced and the cause of the GVT trajectory repetitions, which occur in certain combinations of constant (C) angular velocities of the inner and outer frames in the RPM, was identified. A countermeasure for the trajectory repetition was also developed. The linear sawtooth (LS) and parabolic sawtooth (PS) time-varying angular velocity profiles for the outer rotational frame were suggested to prevent concentration of the GVT trajectory, and their effectiveness was numerically verified using an in-house program. Furthermore, appropriate RPM operating conditions for simulating the hypogravity fields were proposed for the Moon and Mars. The mathematical theory presented for the first time in this study can be extended as an important theoretical background in research on the bioreactor, which can be applied to enhanced three-dimensional cell culturing conditions using the RPM.