A year ago Japan's satellite program suffered a setback, when the launch of the third bird was delayed for six months because of hardware problems. Japan had long refrained from launching military satellites, but this changed when North Korea fired a ballistic missile over Japan in 1998. Japan promptly set out to get eight surveillance satellites in orbit by 2006, in order to keep an eye on North Korean nuclear weapons and ballistic missile efforts. While two Japanese satellites were launched in early 2003, another two more were destroyed during late 2003, when the rocket malfunctioned.
Japan has long relied on commercial photo satellites, and whatever they could get from the Americans. But for high resolution shots, on demand, of North Korea, and electronic eavesdropping from space, they need their own spy satellites. It is believed that the Japanese spy satellites are also being used to watch military developments in China and Russia.
The Japanese program has cost about two billion dollars. The optical satellites weigh about a ton, while the radar ones weigh about a third more. The United States provided a lot of technical assistance on the design and construction of the satellites. Japan built its own rockets to launch them. Like most spy satellite users, Japan does not report on how effective they are. So it's not known if the Japanese had accurate information on this past years North Korean ballistic missile launches.
Japan recently launched the third of four planned spy satellites. The first two were launched in 2003, the last one will go up next year. The one recently launched was the second of two optical reconnaissance satellites. The cameras on board can make out objects as small as one meter in diameter. The best U.S. spy satellites can make out much smaller objects, but for Japan's needs, one meter is adequate. The other two birds carry radar, providing all weather coverage. Technically, the satellites are in violation of a 1969 Japanese law, which mandated Japan to only use space for non-military purposes. To get around this, these birds are technically non-military, and are not controlled by the military.