The advanced LE-7A engine was in its seventh test at Japans Tanegashima Space Center test stand when higher than programmed temperatures in the engines thrust chamber were detected by computers, which ordered an automatic cutoff of the test.

Japanese engineers found 12 small holes in the nozzle skirts cooling tube when they dismantled the engine late last week.

Because of the holes engineers speculate that liquid hydrogen leaked from the cooling system, causing a much higher temperature in the resulting combustion.

The engine burns liquid hydrogen and liquid oxygen much like the U.S. Space Shuttle Main Engine and the French Ariane 5 core Vulcane engine. Engineers said Monday they are continuing the investigation into the cause of the holes and why they were not discovered earlier.

NASDA said it may be that the engines nozzle cannot withstand multiple firings before requiring replacements in such subsystems as the cooling lines. Planned for use aboard the advanced H-IIA expendable launcher, the engine along with the rocket is discarded during a single flight.

Thus reuse of the coolant system should not pose a flight issue to continued development of the rocket.