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). It used a Long Tank Thor first stage, a Mitsubishi Heavy Industries-designed LE-3 engine on the second stage, and three Castor SRMs. Seven were launched between 1975 and 1982, before it was replaced by the N-II. Six of the seven launches were successful, however on the fifth flight, there was recontact between the satellite and the third stage, which caused the satellite to fail.
Mock up of N-1
Castor is a family of solid-fuel rocket stages and boosters built by Thiokol and used on a variety of launch vehicles. They were initially developed as the second-stage motor of the Scout rocket. The design was based on the MGM-29 Sergeant, a surface-to-surface missile developed for the United States Army at the Jet Propulsion Laboratory.
Castor 30 rocket motor being ground-tested
A Castor 120 that will be used as Stage 0 of a Minotaur-C rocket