Experimental Method for Determining Ball Bearing Lubricant Quantity Factor  Yoshimi R. Takeuchi*, Peter P. Frantz * and T im  P. Woodard*  Abstract  Ball bearing temperature prediction methods for spacecraft applications require, in part, a knowledge of the  lubricant contribution to bearing drag torque. This  can be estimated using a model derived by Palmgren  and Snare. When implemented in bearing analysis software, the viscous drag torque model depends on a  variable known as the Lubricant Quantity Factor (LQF ). This value is critical to understanding spacecraft  ball bearing temperatures for cases where motion is involved. In this paper, we describe the results of  experiments that were conducted on a bearing test fixture that is capable of measuring bearing thermal  parameters including heat generation of an operating bearing . The heat generation and speed  measurements are used to determine bearing drag  torque, which is then used to determine LQF . We show  that the LQF depends on operating conditions, and that this variability should be considered when  calculating bearing drag and operational temperature.   Introduction  There are two main bearing parameters that contribute to the final bearing temperatures in a spacecraft  bearing: bearing thermal conductance and heat generation . Bearing thermal conductance has been written  about in the past by this research group [1]. Heat generation caused by energy lost to bearing drag is  used  in this paper to deduce changes in viscous component of drag torque.   Heat generation can be calculated as  the product of torque and speed . Speed is often easily experimentally  measured. T orque can be estimated using a  computational  bearing analysis program , discriminat ing  between  the two main contributors t o total energy loss: mechanical and lubricant torque. The mechanical  contribution is due to the resistance to motion from the Coulombic friction forces at the rolling and sliding  interfaces between the ball, races, and cage . By contrast, the lubricant is due to resistance from the viscous  friction caused by the ball “plowing through” the lubricant . The mechanical torque is often better known,  because  the parameters needed for its calculation are easily  obtainable . These include the bearing  geometry, materials properties, and loading configuration.   Some of the same properties are necessary to calculate the viscous drag torque due to the lubricant .  However, one required value that is not easily determined in the des ign phase is the lubricant quantity factor  (LQF). In bearing models of viscous drag, the LQF is a multiplication factor that scales the torque output of  a bearing due to the energy lost to plowing through the lubricant . It is a dimensionless parameter that  is  intended to be directly related to the quantity of oil in the ball, race, and cage interfaces that contributes to  the viscous drag of the system . Only a small fraction of the lubricant in a typical bearing contributes to these  losses at the critical in terfaces in the ball path. The rest of the lubricant is held in reserve elsewhere in the  bearing,  where it does not interfere with motion. Since the fraction of oil in the ball path is not easily  measured or controlled, the LQF cannot be deduced a- priori.   To find an explicit value for the LQF, one typically must conduct an actual bearing test, measure the total  bearing drag, subtract from this the mechanical drag, and solve for the LQF . Torque data is collected after  run-in conditions have been met , upon w hich the bulk quantity of bearing lubricant is often assumed to be  fixed throughout the range of operating conditions that are expected for the mission requirements . When  calculated this way, all of the drag torque that is not caused by the nominal mechanical drag is ascribed to  the lubricant, and the calculated LQF value depends linearly on this residual torque.   *The Aerospace Corporation, El Segundo, CA Proceedings of the 44th Aerospace Mechanisms Symposium, NASA Glenn Space Flight Center, May 16-18 , 2018 NASA/CP—2018-219887 543