N-I (rocket)

The N-I or N-1 was a derivative of the American Thor-Delta rocket produced under license in Japan. The "N" stood for "Nippon" (Japan). The vehicle used a Long Tank Thor first stage derived from the PGM-17 Thor intermediate-range ballistic missile, a Mitsubishi Heavy Industries-designed engine on the second stage, and three Castor 2 solid rocket motors. An optional third stage, the Star-37N solid motor, was used on three of the seven launches.

Seven N-I rockets were launched between 1975 and 1982, after which the vehicle was replaced by the N-II. Six launches were successful. The fifth flight failed after the payload and third stage collided shortly after separation.

On 29 February 1976, the second N-I launch conducted the only orbital launch on a leap day, as of February 2024.