Japan claims its project is the biggest since the Apollo missions put the first humans on the moon. China, hoping to pave the way for its own manned missions, says its probes will study the lunar surface to help plan a landing.
But the big question right now is not about science — it's who will get there first.
Japan's space agency said last week its SELENE lunar satellite is on track for a Sept. 13 launch, following years of delay as engineers struggled to fix a slew of mechanical problems. China, meanwhile, was rumored to be planning a September launch for its Chang'e 1 probe, but is being coy as to the exact date.
Both sides say all systems are "go."
The Chinese satellite and its Changzheng 3 rocket carrier have passed all tests and construction of the launch site is finished, according to the National Space Administration's Web site. Last month, China's minister of defense technology told CCTV that all was ready for a launch "by the end of the year."
Officials have tried to play down the importance of beating each other off the pad, but their regional rivalry is never far below the surface.
"I don't want to make this an issue of win or lose. But I believe whoever launches first, Japan's mission is technologically superior," said Yasunori Motogawa, an executive at JAXA, Japan's space agency. "We'll see which mission leads to the scientific breakthroughs."
China's military-run space program has taken a great leap forward in recent years, and Beijing sent shock waves through the region in 2003 when it became the first Asian country to put its own astronauts into space.
China also raised eyebrows when it blasted an old satellite into oblivion with a land-based anti-satellite missile, the first such test ever conducted by any nation, including the United States and Russia.
But Japan has stayed close on China's heels.
After a decade of work, Tokyo in February completed a network of four spy satellites that can monitor any spot on the globe, every day — a program spurred by the 1998 North Korean test of a Taepodong ballistic missile that flew over Japan's main island and into the Pacific.
One of the spy satellites has since failed, however, throwing the network's effectiveness into doubt. Still, Tokyo spends about $500 million a year on its spy satellites.
Regional powers India, South Korea, Malaysia and Taiwan all have satellites in orbit. North Korea claims to have sent one up with its 1998 ballistic missile launch and to have used it to broadcast hymns about its leader, Kim Jong Il. The claim has never been substantiated.
But the planned lunar missions by China and Japan are among the most ambitious space programs yet.
Japanese space officials have said their 32 billion yen ($276 million) 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.
SELENE involves placing a main satellite in orbit around the moon and deploying the two smaller satellites in polar orbits to study the moon's origin and evolution. Japan launched a lunar probe in 1990, but that was a flyby mission — unlike SELENE, which is intended to orbit the moon.
China's Chang'e 1 orbiter will use stereo cameras and X-ray spectrometers to map three-dimensional images of the lunar surface and to study its dust. The country has already spent 1.4 billion yuan ($185 million) on the undertaking, according to the official Xinhua News Agency.
Beijing hopes to retrieve samples from the moon in later missions, according to the project's Web page, and Xinhua has reported that a manned probe could come within 15 years. Japan is also considering a manned mission by 2025.
"It's the race for the South Pole, all over again," said Hideo Nagasu, former research head of JAXA's predecessor organization, the National Aerospace Laboratory.
"In the interest of furthering Asia's space technology, cooperating would be the best option. But I don't think either side wants to do that just yet."