The June 21 failure of a Volna rocket that destroyed the Planetary Society‘s solar sail experiment was caused by premature shut-down of the first-stage engine.

In its report to the Russian space agency Roskosmos, the failure review board convened by the Makeev Rocket Design Bureau, manufacturers of the Volna, said the shutdown was caused by a “critical degradation in operational capability of the engine turbo-pump.”

The engine shut down after firing for 82.86 seconds, instead of the expected burn of approximately 100 seconds. The first and second stages never separated and, as a result, the spacecraft propulsion system did not fire. Hence, the Cosmos 1 solar sail did not separate from the third stage.

The review board included members from Makeev, the Lavochkin Association, which built Cosmos 1, and Tsniimash, a lead engineering center of the Russian space agency. The Planetary Society was not invited to be part of the board.