Evaluation of durability for cryogenic high-speed ball bearings of LE-7 rocket turbopumps(c)

The durability of the cryogenic high-speed ball beatings of liquid oxygen (LO(2))/liquid hydrogen (LH(2)) turbopumps used in the LE-7 rocket engine was evaluated based on findings of wear inspection, X-ray photoelectron spectroscopy (XPS) analysis of PTFE (polytetra-fluoroethylene transfer-film as a lubricant, and the bearing temperatures detected during engine firing. The turbopump bearings inspected were used in a series of engine firing tests. The wear inspection results indicated that excellent lubricating conditions without severe wear were obtained for both LO(2) and LH(2) turbopump bearings. The LO(2) turbopump bearings showed relatively higher wear than that of the LH(2) turbopump bearings operated at high speeds. Results of XPS analysis suggested that, particularly in a reduction environment of LH(2), metal fluoride was able to form at the transfer film/bearing steel interface, resulting in an increase in the durability of the PTFE transfer film and a consequent reduction of wear in comparison with the case in LO(2).