TOKYO — Japan’s Ministry of Defense (MoD) intends to invest in new missile warning and other surveillance-related capabilities to counter what it sees as a growing threat from North Korea and China, according to budget documents.

In part because of pressure from the United States to contribute more to their military alliance, Japan also plans to make a modest investment in space situational awareness capabilities next year, according to the MoD.

Missile warning has been identified as a priority for Japan since the passage of a law that gives the MoD more leeway to develop space-based capabilities, which had been strongly discouraged by a longstanding policy. The MoD has been studying missile warning satellites since 2009, but in the wake of North Korea’s latest missile test in April, aerial sensors are being looked at as well, documents show.

The MoD’s budget request for the upcoming fiscal year, which begins in April, includes 3 billion yen ($37 million) to examine airborne missile warning options, the documents say.

Both the space-based and airborne sensor programs are aimed at detecting ballistic missiles with ranges of about 1,000 kilometers, the MoD said Nov. 6 in an emailed response to SpaceNews questions. The MoD declined to say when it might test an aerial missile warning sensor but said it plans to fly an experimental space-based sensor, possibly as a piggyback payload.

The addition of the aerial program reflects increased anxiety about North Korea in particular, said space analyst Norihiro Sakamoto, a research fellow at the Tokyo Foundation.

The North Korean missile test brought Japan’s deficiencies in missile warning into stark relief. The MoD failed to track the missile, which broke up shortly after launch, despite placing three naval ships equipped with the U.S.-supplied Aegis Ballistic Missile Defense system directly under the rocket’s expected flight path.

Japan continues to rely on the United States for early warning, and the failure to demonstrate the independent tracking capability has forced the MoD to look at other options, Sakamoto said.

In addition to concerns over North Korea, Japan has a territorial dispute with China over a tiny group of islands — called Senkaku by Japan and Diaoyu by China — that has flared up in recent years.

The aerial sensor program could have maritime surveillance applications as well.

“In Japan, we feel real or potential threats from not only North Korea but also China and Russia,” Sakamoto said Nov. 5. Independent communications, surveillance and reconnaissance capabilities are a high priority for Japan, he said.

“Missiles from the neighborhood come within 10 minutes; therefore we need to detect them in minutes. Unmanned planes [or even airships] could be useful not only for missiles but also to watch areas like the Senkaku Islands continuously,” Sakamoto said.

Meanwhile, the MoD plans to invest 140 million yen next year to develop an independent space situational awareness capability, an effort that entails modifying an existing FPS-5 phased array radar to track space objects, according to its budget request. The MoD did not give further details about the program.

The move is mainly in response to the Japan-U.S. Security Consultative Committee meeting this past April, in which the U.S. government asked the MoD to develop such a capability, the MoD said in its email.

“There is a strong political pressure for MoD to take this program because of American demand for a military-to-military program,” said Kazuto Suzuki, an expert on Japanese space policy and an associate professor at the Hokkaido University in Japan. “I believe that it is largely because of the information sharing issue with U.S. military, which is understandable given the sensitivity of [space situational awareness] data.”

Suzuki said the relatively modest investment in the radar modifications reflects the fact that space situational awareness is a lower priority than communications, intelligence, surveillance and reconnaissance capabilities. “The MoD has found that the best way of dealing this issue is to use existing FPS-5 for [space situational awareness], so that the investment is minimized to the cost of testing,” he said.

A graduate of the Columbia Graduate School of Journalism, where he won the Horgan Prize for Excellence in Science Writing, Paul Kallender-Umezu is co-author of “In Defense of Japan: From the Market to the Military in Space Policy” (Stanford University...