A government committee approved the date for the final launch in Japan's 250 billion yen (2.1 billion US dollar) project to put four spy satellites into full operation this year, officials said.
"There is no knowing about what will evolve in the international situation surrounding Japan," Chief Cabinet Secretary Yasuo Fukuda said in a speech before the committee on development of intelligence-gathering satellites. "I wish that you will continue to tackle the project by bracing up your spirits."
North Korea denounced the March 28 deployment of the first two satellites as a "hostile act" which could trigger a renewed arms race.
The project is intended as a response to North Korea's firing of a suspected Taepodong ballistic missile over Japan and into the Pacific in August 1998, a move which sent shockwaves around the region.
The new satellites, one with optical sensors and another with all-weather radar imaging capabilities, are identical to those already in orbit.
The first two satellites pass over North Korea twice a day, at morning and night. The two new satellites will also enable Japan to photograph North Korea during the afternoon.
These satellites can identify objects as small as one metre (yard) in length, matching the technology of current commercial imaging satellites, but they are not as good as US military satellite hardware.
The second pair of satellites will also be launched from the Tanegashima Space Center on the isle of Tanegashia lying south from the southern Japan island of Kyushu.
The radar imaging satellite can take pictures even at night and in cloudy conditions. Researchers expect it will be able to distinguish camouflaged vehicles and facilities.