People familiar with the plans tell The Associated Press the trip will happen as early as this month.
Last month, North Korea shot a satellite into space on the back of a three-stage rocket in defiance of a U.N. ban. Washington and others decried it as a covert test of ballistic missile technology and are seeking U.N. Security Council action against Pyongyang.
Nuland said Schmidt and Richardson were "well aware" of the U.S. government's views. She said they would be traveling as private citizens and carrying no messages from Washington.