The Japanese Aerospace Exploration Agency said Wednesday that the largest moon mission since the U.S. Apollo program is on track to launch on Sept. 13 following repairs to a problematic lunar probe.

The Selenological and Engineering Explorer (SELENE) probe was originally scheduled to be carried aboard an H-IIA rocket on Friday to orbit the moon. But the agency discovered improperly installed condensers last month during an inspection of two smaller satellites that accompany the main orbiter.

"Testing showed the parts were functioning normally, but we decided it was better to be safe than sorry," JAXA spokesman Tatsuo Oshima said. "We have every confidence that the mission is now on track."

The probe would have been unable to carry out one of its 14 projects — measuring the moon's gravity field — if the the condensers malfunctioned, Oshima said.

The ¥32 billion probe's mission is already four years behind schedule. Japan's last lunar project was a flyby mission in 1990.

The LUNAR-A moon shot was to have been launched in 2004 but was canceled after repeated delays caused by mechanical and fiscal problems.

The SELENE project is the largest lunar mission since the U.S. Apollo program in terms of overall scope and ambition, outpacing the former Soviet Union's Luna program and NASA's Clementine and Lunar Prospector projects, Oshima said.

The mission involves placing the main satellite in orbit at an altitude of about 100 km and deploying the two smaller satellites in polar orbits.