Blind Spots in Communication Infrastructure for the Defense of the Nansei Islands

The Ministry of Defense has released the contract details for the next-generation satellite communication system worth 123.5 billion yen ordered from Mitsubishi Electric. This satellite, which is set to begin operations by March 2030, will inherit the X-band communication capabilities of the "Kirameki 2" launched in 2017, while also incorporating a new feature of variable beam coverage through a digital payload.

At first glance, this appears to be a routine equipment update indicating an improvement in the Self-Defense Forces' communication capabilities. However, from the perspective of the author, who has faced the communication systems of the escort fleet in the Japan Maritime Self-Defense Force for 25 years, this contract reveals a structural problem: the vulnerability of communication infrastructure in the defense of the southwestern islands.

The currently operational "Kirameki 2" serves as an X-band satellite in geostationary orbit, primarily responsible for communication with naval vessels at sea and units on remote islands. The X-band is a frequency range suitable for military communications, being more resistant to rain attenuation compared to the commercial Ka-band, and allowing for smaller antenna sizes. However, geostationary satellites have a critical weakness: their vulnerability as a single point of failure (SPOF).

Since China's satellite destruction test in 2007, it has accelerated the development of anti-satellite (ASAT) capabilities. In addition to ground-launched kinetic energy weapons like the SC-19 and DN-3, recent reports have confirmed the presence of "killer satellites" in orbit that can interfere with operations. Communication systems that rely on a single satellite in geostationary orbit are the first to become targets in times of crisis.

Mitsubishi Electric's emphasis on "variable beam coverage" is a partial solution to this problem. In the traditional fixed beam method, radio waves could only be directed to pre-set areas. The new digital payload allows for changes in beam shape and output during operation, enabling focused coverage on Yonaguni Island and Ishigaki Island, for example. This represents a technological advancement in efficiently allocating limited communication capacity.

However, the fundamental problem remains unresolved. In a simulation exercise conducted by the author at the National Defense Medical College in 2018, the impact of losing satellite communication on the defense of the southwestern islands was examined. The results were more serious than expected. While the Japan Maritime Self-Defense Force's escort ships can switch to high-frequency (HF) communication, the Japan Ground Self-Defense Force's anti-ship missile units and the Japan Air Self-Defense Force's radar sites are highly dependent on satellite communication. In particular, the improved version of the Type 12 anti-ship guided missile (with a range of over 1,000 km) requires immediate transmission of target information, and without satellite communication, it would lose most of its capabilities.

The U.S. military is attempting to address this issue with low Earth orbit (LEO) satellite constellations. In addition to plans to militarize SpaceX's Starlink, the Department of Defense is deploying hundreds of small satellites as its own Transport Layer. LEO satellites are more susceptible to destruction due to their lower orbital altitude, but the large number of satellites can complement each other, allowing the overall communication network to be maintained even if one or two are lost.

Japan should consider a similar approach, but in reality, there are budgetary and technical constraints. The contract amount of 123.5 billion yen is reasonable for a single GEO satellite system, but constructing a LEO constellation with hundreds of satellites would require an extraordinary investment. The Ministry of Defense's budget for space-related projects is about 100 billion yen annually, making it impossible to focus investment solely on satellite communication.

A more realistic option is to ride on the U.S. military's Transport Layer. Joint use of the WGS (Wideband Global SATCOM) satellites is already progressing between Japan and the U.S., and the Self-Defense Forces are using some X-band transponders. Similarly, by deploying ground terminals that connect to the U.S. LEO military communication network, redundancy can be secured without large-scale satellite development.

However, there is another issue: the problem of communication sovereignty. Relying on U.S. systems means that the availability of communication in times of crisis would be subject to U.S. political decisions. In the scenario of a Taiwan contingency, it is uncertain whether the U.S. military would provide communication support in advance before Japan exercises its collective self-defense rights and joins the conflict.

The new satellite, scheduled to begin operations by 2030, will technically be an excellent system. The flexibility of variable beams will aid not only in efficient operations during peacetime but also in prioritization during emergencies. However, strategically, the very structure of relying on a single GEO satellite is becoming outdated.

What concerns the author most is the "deferred structure" indicated by this contract. It seems to postpone fundamental discussions about integrating LEO constellations and U.S. systems, opting instead for a conventional satellite update. While it is understandable that technical considerations take time, there is a significant possibility that by the time operations begin in 2030, this satellite will already be strategically obsolete.

Can the anti-ship missile units in the southwestern islands continue to fight after losing their "eyes and ears" due to a Chinese ASAT attack? The Ministry of Defense should prepare an answer to this question now. The establishment of alternative communication means in the event that satellites become unusable is, in the author's view, a more urgent issue than merely improving the performance of the satellites themselves.