An investigation lasted a month and found that the part that failed had been tested 8,000 times previously without failing, and the Soyuz engine had fired some 2,000 times since 1967, also without a single failure. But the engine was modified for the next flight, and a vacant Soyuz with the newly modified engine, Soyuz 34, was sent to the orbiting Salyut for the crew there to return with.[2]