A booster-nozzle hole was to blame for the failed launch of an H-IIA rocket in November, the nation's space agency said Friday.
A hole in the nozzle's outer wall, made up of reinforced carbon fiber, caused a leak of fuel gas that prevented a wire from functioning normally and separating the booster from the H-IIA, the Japan Aerospace Exploration Agency told the government's Space Activities Commission.
The agency encountered similar problems in developing the booster in question, and had strengthened the outer part of the booster nozzle in response.
The nozzle is a rocket engine part that accelerates the exhaust gases from the combustion chamber to a high velocity.
JAXA is now trying to reduce fuel-gas emission pressure, especially on the nozzle, in developing a new booster.
The H-IIA is central to Japan's space program. The agency launched the domestically developed rocket on Nov. 29 from the Tanegashima Space Center in Kagoshima Prefecture, seeking to send two satellites to spy on North Korea.
The mission failed when the launch vehicle was deliberately destroyed by the ground crew shortly after liftoff, with one of the two boosters having failed to disengage after burning off its fuel.