With the rapid progress in technological innovation, the nature of war has been drastically changing as new realms such as outer space, cyberspace and electromagnetic waves emerge.
How will the current Japan-U.S. alliance forged 60 years ago deal with these changes?
"We're going to work with the U.S. military and have satellites expose everything," Prime Minister Shinzo Abe told officials in mid-June shortly after the government decided to suspend procedures to deploy the Aegis Ashore land-based missile interception system.
After Abe made his remarks, a missile interception system using the Hypersonic and Ballistic Tracking Space Sensor (HBTSS) -- a space surveillance network that the U.S. military is planning to introduce -- has surfaced as a prime candidate during discussions led by Japan's National Security Council on relevant matters including an alternative missile defense system, according to sources.
According to a senior official of the U.S. Missile Defense Agency, HBTSS is designed to monitor the entire world and track enemy missiles from the boost phase through the terminal phase. To do so, more than 200 small satellites will be launched into low orbits at altitudes of several hundred kilometers to 2,000 kilometers to create a satellite constellation where all the satellites work together in a system.
Small satellites weigh about 100 kilograms to 500 kilograms. The smallest ones can be a little as 10 centimeters square. With the private sector taking part in the industry, more small satellites have been launched, accelerating studies on their use for security purposes.
Under the scenario of using the satellite constellation, sensors installed on each satellite track enemy missiles and share the information in real time with ground- and sea-based missile control systems for launching interceptor missiles. Then an interceptor missile will be fired from the most suitably located Aegis-equipped destroyer or other launch pad.
Ground- and sea-based radars, which the current missile defense system relies on, are designed to detect ballistic missiles flying on a high trajectory. Therefore, it is difficult to track China's hypersonic glide vehicles, which can fly at relatively low altitudes in the atmosphere at more than five times the speed of sound while avoiding enemy radar networks, and North Korea's new missiles.
To deal with this situation, HBTSS is expected to be able to fully track these missiles through its commanding view from outer space.
The U.S. military aims to establish an initial satellite constellation in fiscal 2022 (October 2021 to September 2022), before starting first-stage operations in fiscal 2024.
To realize the plan, however, Washington needs to overcome a huge financial burden estimated at more than 1 trillion yen, in addition to such technical problems as connecting the sensors and missile control systems.
"Tokyo has begun discussions on the [HBTSS] plan with Washington, following the report last year that North Korea developed a new missile that can fly at low altitudes on an irregular trajectory," said a senior Japanese government official.
Japan is considering partially joining the satellite constellation to have the U.S. military share information, sources said.
This satellite constellation will go beyond defensive purposes.
A senior Pentagon official said on June 4 at a seminar for U.S. congressional officials that the second purpose of introducing HBTSS is for sighting of moving targets on land and sea, stressing its use for offense.
If the plan is realized, and Japan-U.S. cooperation proceeds, the satellite constellation could possibly serve as the eyes of Japan when the country tries to strike an enemy base that is firing missiles.
In fact, Abe's remarks to "have satellites expose everything" also implied that the system would enable Japan to identify targets to attack.
According to sources, the prime minister continued by saying, "If we will be able to launch missiles precisely, that will be our deterrent."
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