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In a report released yesterday China finally revealed that a turbo pump design issue in one of Long March 5’s two first stage engines caused that rocket’s launch failure in July.
The State Administration for Science, Technology and Industry for National Defense (SASTIND), which oversees China’s space activities, released a report April 16 attributing the failure to a turbopump on one of two liquid-oxygen and hydrogen YF-77 engines powering the rocket’s first stage. The turbopump’s exhaust structure, according to SASTIND, failed while under “complex thermal conditions.”
Redesigned YF-77 engines have already been through hot fire testing at a site in a ravine near Xi’an in north China. The tests have verified the effectiveness of the measures taken, according to the report.
Unfortunately, the report is in Chinese, so I can’t read it. It does appear that the problem was a difficult one that required an engine redesign. That they have solved it is demonstrated by the release of this report. China’s space program functions like the old Soviet Union’s. Details about serious problems were only released, if at all, once the program had successfully overcome them