A method for determining the onset of a thermally induced convective mixing motion in a model of a cylindrical space-storage tank subjected to a constant heat flux at its outer boundary. The model simulates a completely filled liquid cryogen tank with shear-free ends rotating in a low-gravity environment. The governing disturbance equations reduce to a self-adjoint eigenvalue problem for the critical Rayleigh number (the stability criterion). Using the Rayleigh-Ritz technique of approximating eigenvalues with an equivalent variational principle, the critical Rayleigh number is calculated as a function of the Taylor number (ratio of Coriolis forces to viscous forces) and the aspect ratio (length-to-diameter ratio) of the cylindrical tank. Results indicate that the critical Rayleigh number is a monotonically increasing function of the Taylor number and a monotonically decreasing function of the aspect ratio. It is found that relatively small rotational speeds will initiate and maintain a thermally destratifying convective motion within a vessel filled with liquid hydrogen. This method of mixing has the advantage of having no moving parts within the tank. It also provides a means for thermal control of space-storables. 31 pp. Refs.