The other was a demonstration satellite to collect data for research and development. The H-IIA rocket blasted off from the southern island of Tanegashima around 1:40 pm (0440 GMT) and released the satellites as planned, according to the Japan Aerospace Exploration Agency (JAXA).
“The rocket flew as planned and released both satellites,” JAXA said in a statement, confirming its success.
From an altitude of several hundred kilometres, the radar satellite will be able to detect objects on the ground as small as a square metre, including at night and through cloud cover.
Prime Minister Shinzo Abe, who has taken a hardline stance on North Korea, hailed the successful launch.
“The government will make the most use out of the system… in order to enhance our country’s national security and crisis management,” he said in a statement, according to national broadcaster NHK.