Mitsubishi Heavy Industries has won its first commercial order to launch a satellite on an H-IIA rocket, a deal that officials hope will grow into a business that could support Japan’s cash-strapped space program.

The agreement with a South Korean entity to launch sometime after April 2011 comes less than two weeks before the Japan Aerospace Exploration Agency plans to put eight satellites into orbit to show that the homegrown H-IIA can compete with rivals in Russia, the United States and Asia’s new space powerhouse, China.

Japan’s space program has long been focused entirely on carrying government-sponsored, unmanned payloads — mainly scientific, telecommunications and spy satellites, which it first launched 10 years ago — into orbit.

But officials are hoping that commercial use will help fund Japan’s long-term space program, which the government believes is an essential part of national security.

The primary mission of the Jan. 21 launch from Tanegashima Island in Kagoshima Prefecture is to send into orbit a greenhouse-gas monitoring satellite called Ibuki (Breath). But along with the main payload, the rocket will carry seven “baby satellites” — one developed by JAXA and six created by university research centers and private industry.

JAXA decided to open the payload up to the private sector because it had extra launching power and wanted to display its capabilities for commercial use.

“If we can successfully launch the seven mini satellites, this could be an excellent precedent for commercial use in the future,” said Asaka Hagiwara, spokeswoman for JAXA.

In a promising sign, Mitsubishi Heavy Industries Ltd., which makes the H-IIA, signed an agreement Monday with the Korea Aerospace Research Institute to carry its multipurpose Arirang 3 satellite into space. It was the first commercial order for use of a Japanese-made rocket. The price was not disclosed.

The H-IIA was initially designed and built as a government project in which Mitsubishi Heavy took part. The rocket project has since been privatized as a business of MHI, now considered a vital part of Japan’s space program.

Japan has long been one of the world’s leading space-faring nations — having launched its first satellite in 1970 — but it has been struggling to get out from under China’s shadow in recent years and gain a niche in the global rocket-launching business, which is dominated by Russia, the U.S. and Europe’s Arianespace.

Becoming a commercial space power would help Japan keep pace in the intensifying Asian space race.

Struggling under a relatively small budget — ¥188 billion in 2008 — Japan has watched China march ahead with high-profile manned flights and is now seeing a growing rival in India, which has set its sights on reaching the moon.

China has already built up lucrative commercial satellite launching services. It launched a communications satellite for Nigeria in 2007 and another for Venezuela last year.

Japan is keenly aware its space program has crucial implications for national security.

Lance Gatling, an independent space and defense expert, said that while commercial success would be nice, Japan believes it needs to keep its rocket program in good shape for defensive reasons.

“They want to be able to launch a satellite and not tell anybody where it’s going. There are many reasons to do that,” he said, referring to North Korea and other regional concerns. “If it was a commercial business, it would have been shut down years ago.”

Underscoring the military realities, the Diet last year voted to allow the space programs to be used for defense for the first time. The law, one of several recent moves to give greater freedom to the armed forces, allows the military to develop advanced spy satellites for intelligence and a missile defense shield being built jointly with the United States.

Japan’s current spy satellite program is run by a civilian agency.

JAXA official Takao Eto, who is in charge of coordinating the piggybacks, said the agency has already selected four other piggybacks for a launch in 2011. They will be launched for free, but JAXA is considering charging a launch fee in the future.

Takeshi Maemura, head of space systems for Mitsubishi Heavy, said Japan’s launch cost has come down to a competitive level.

He said the standard for a competitive launch — largely set by Russia’s Proton rocket — used to be around ¥7 billion but has now risen to around ¥9 billion.

JAXA said this month’s launch will cost about ¥8.5 billion — the lowest ever.

“The cost has reached a level where we can be quite competitive,” Maemura said.