TOKYO (AP) -- Japan's latest rocket was readied on the launch pad Monday night, the eve of a scheduled blast off aimed at taking two probes into space.

The rocket shot suffered two earlier setbacks when glitches forced Japan's space agency to replace its main engine and twice call off test countdowns.

But Tuesday's early morning launch was expected to go ahead as planned from Japan's launching site on the remote southwestern island of Tanegashima, said Shintaro Nishihira, a spokesman for the National Space Development Agency.

The H-2A rocket program is the centerpiece of Japan's attempt to break into the commercial satellite launching business and compete with the United States and Europe. But the two-stage, black-and-orange rockets have been plagued by problems, including a February launch that left one of its probes lost in space.

Test countdowns for the current rocket were called off twice late last month when engineers detected problems with a fuel valve and a gauge that monitors the flow of liquid oxygen to the engines.

In July, NASDA had to completely replace an engine on the 10.2 billion yen ($5.7 million) rocket because of flaws in valves and the sealant used between rocket stages.