TOKYO: A power system problem seems to be behind last week’s shocking failure of a Japanese flagship H3 rocket launch.

The launch of the No. 1 unit of the H3 rocket failed on Tuesday as its second-stage engine did not ignite, disappointing the Japan Aerospace Exploration Agency (JAXA), Mitsubishi Heavy Industries Ltd. and others concerned.

The development marked the sixth failure of Japan’s flagship rocket since the late 1990s.

The previous five failures were all caused by mechanical problems such as pump or nozzle damage.

But this time, abnormality in the power system was found from data transmitted during the flight. If it was caused by an electric or computer-based automatic control system, that would be the first such case.

Of the five previous failures, three involved liquid-fueled rockets like the H3 rocket, namely the H-2 No. 5 and No. 8 units and the H-2A No. 6 unit. The remaining two cases were solid-fueled rockets, namely the M-5 No. 4 unit and the Epsilon No. 6 unit.

Nagoya University designated professor Koichi Matsuyama was stunned to learn that the second-stage engine of the H3 No. 1 unit did not ignite.

“I never thought that the second stage, which has a proven track record, would fail,” said Matsuyama, former head of the liquid-fueled rocket engine design division at Mitsubishi Heavy. He was involved in the development of the H-2 and H-2A rockets.

The LE-5B-3 second-stage engine used in the H3 No. 1 unit burns liquid hydrogen and liquid oxygen to eject gas. Its first version was developed for the H-1 rocket, whose No. 1 unit flew in 1986.

The current version is the fifth generation, incorporating a series of improvements. The engine, used in the second stage of H-2, H-2A and H-2B rockets, has high performance and extremely high reliability.

The engine had caused a launch failure only once, at the time of the H-2 No. 5 unit in 1998. At that time, a crack opened in the combustion chamber due to a manufacturing error, causing hot combustion gas to leak and burn off electric power wiring.

The LE-5B-3 engine has undergone improvements such as extended combustion time.

Matsuyama wonders whether there was a problem with electronic components, an error in the assembly process for electronic equipment, or a problem with the circuit design that could not be found during tests.

If potential causes can be narrowed down through detailed data analysis, it may be possible to identify the real one by examining the second stage for the H3 No. 2 unit.

If it takes time to identify the cause and fix the problem, the launches of the No. 2 and later rockets will be delayed. The impact would be significant if such delays affect the launches of a probe to retrieve samples from Phobos, a moon of Mars, and a new spacecraft that transports supplies to the International Space Station.

JIJI Press