Spin axis tilt in the Geostationary Meteorological Satellite of Japan

Conclusions reached in analyses of the causes of a large spin-axis tilt on the GMS-1 spacecraft are reported. An oscillatory component of the 1.5-3.2 deg tilt is attributed to convection currents of the propellant in the reaction control system lines. The problem arose when the outer manifold became significantly warmer than the inner manifold, and was solved by shutting off the propellant line heaters and lowering the manifold temperature. Changes were introduced into the loop nutation damper design of the GMS-2 spacecraft to eliminate the 1.75 deg displacement of the spin axis from its design point. An increase in damper offset was introduced to compensate for the elimination of propellant migration.