Russia on Friday blamed a one-off production fault in a rocket engine for the crash of an unmanned spaceship last month but nevertheless ordered checks of all similar rocket motors.
The Russian space agency Roskosmos said in a statement that the motor of the third-stage rocket blasting the craft into orbit failed because a blocked duct cut fuel supply to its gas generator.
The Progress spaceship, an unmanned cargo vessel carrying supplies for the International Space Station (ISS), crashed into Siberia last month instead of reaching orbit.
The engine defect in the Soyuz-U rocket led to a "lowering of the performance of the engine and its emergency shutdown," Roskosmos said, reporting the findings of a commission of experts.
"The commission came to the conclusion that the identified production defect was by chance, but a decision can only be taken that it was a one-off after repeat checks ... of all the stock of engines, " it said.
Russia earlier responded to the crash by grounding all Soyuz rockets, the backbone of the national space programme, which are also used to send manned capsules to the ISS.
Roskosmos did not specify when the next Soyuz launches could be, saying it first needed to draw up a schedule for checks and fine-tuning.
Russia said late last month that a launch taking astronauts to the ISS initially scheduled for September 22 would be postponed at least until late October.
The failed Progress launch was a humiliating blow for Russia, which is now the sole nation capable of taking humans to the ISS after the July withdrawal of the US space shuttle.
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