Japan moves to build a signals intelligence satellite to find targets for its counterstrike missiles

Japan's Defence Ministry has decided to start developing a satellite that collects and analyses radio signals from space, with the aim of pinpointing targets for the long-range missiles at the heart of its new counterstrike capability. The Yomiuri Shimbun reported the plan on Monday, 9 November, citing several government and ruling-party officials.

According to the paper, the ministry will begin the work in the next fiscal year, which starts in April 2027. The direction is due to be written into Japan's three core security documents, which the government intends to revise before the end of this year. The ministry has already included related costs in its budget request for fiscal 2027 as an item without a stated amount, the Yomiuri said.

Leaving items unpriced is a broader feature of that request. The ministry's summary of the fiscal 2027 request, published at the end of August, said projects whose shape depends on the revision of the three documents would be listed without figures and settled during the budget process, while spending under the existing buildup plan was put at about 9 trillion yen on an expenditure basis.

The first step, as the Yomiuri described it, is research on sensors that capture and analyse radio emissions, starting next year. By studying the wireless communications and radar signals that travel around the Earth, such sensors are meant to work out where ships, vehicles and military units are and how many there are. The ministry aims to launch a demonstration satellite by fiscal 2031.

The new satellite is intended to fill a gap in the constellation the ministry is already building. That network pairs high-resolution optical satellites with synthetic aperture radar satellites that observe the ground. Images allow detailed identification of a target, but each satellite can watch only a limited area. A signals satellite that covers a wide region would help narrow down where to look, which the ministry hopes will improve its ability to identify targets, according to the report.

Space already features heavily in the fiscal 2027 request. It includes a second space domain awareness satellite designed to track how radio waves are being used in orbit so that threats can be spotted early, research on high-definition infrared sensors to detect and follow hypersonic glide weapons from space, research on a tactical satellite that would use artificial intelligence, and a new satellite development office inside the Acquisition, Technology and Logistics Agency.

Some members of the governing coalition want the intercepted signals used for more than targeting. The Yomiuri reported that there are calls inside the ruling bloc to analyse the content of the radio traffic and feed it into intelligence work. In March, the Liberal Democratic Party's intelligence strategy headquarters asked Prime Minister Sanae Takaichi in a proposal to introduce and strengthen tools for collecting and analysing signals intelligence.

Japan would be catching up with its larger neighbours. The paper said the United States, China and Russia already operate satellites of this kind and are believed to use them both to fix the location of targets and to intercept the content of transmissions. China's Yaogan series, which has been described as a reconnaissance constellation for the Chinese military, is said to include signals collection satellites as well as optical and radar imaging types.

The report did not give a cost, an orbit or the number of satellites Japan eventually plans to field, and the ministry has not announced the programme itself. Those details are likely to depend on the revised security documents and on how the government fills in the unpriced items in its budget plan for the year ahead.