Bubbles in fuel caused crash of H-II rocket, experts claim

Government investigators looking into the crash of an H-II rocket last November said Friday they have determined that the crash was caused by stress caused to a critical engine pump by bubbles in the rocket’s fuel.

Officials of the Space Activities Commission’s technical assessment panel say they are compiling a report on the crash and will present it shortly to the government-appointed commission.

The panel has found that the blades in the turbo engine pump in the H-II rocket were damaged as a result of forces generated by bubbles that built up inside the liquid-hydrogen fuel tank during the rocket’s brief ascent from its launch pad.

The bubbles, combined with what experts believe were shoddy production process in the construction of the rocket, led to the rupture of the blades in the fuel pump, the panel said.

Investigators say they have found tiny cracks in the fuel-pump blades which they believe occurred during the production process.

The National Space Development Agency said it will carry out experiments to ensure that new H-IIA rockets, presently being developed, do not have the same problem.

Space Activities Commission experts said they reached their conclusions after examining the salvaged wreckage of the rocket engine and carrying out tests on bubble formation in fuel.

As the outside atmospheric pressure declined during the rocket’s ascent, launch controllers reduced the pressure inside the fuel tank. This process led to an increase in bubbles inside the fuel pump, triggering a fluctuation in internal pressure that put stress on the engine. This phenomenon was not widely known when the rocket was being developed, but the experts said the problem should have been dealt with in 1998, when a Japanese expert raised the issue.

The H-II rocket crashed after the main engine in the first stage stalled four minutes after it lifted off from Tanegashima Space Center in Kagoshima Prefecture on Nov. 15.

The rocket was carrying a multipurpose government satellite.