H-I

The H-I was a Japanese medium-lift launch vehicle that flew nine times between 1986 and 1992. Its first stage was a licence-built version of the Thor-ELT, originally constructed for the American Delta 1000 rocket and already produced under licence in Japan for the N-I and N-II rockets, while the second stage was entirely Japanese and used the LE-5 engine, the first Japanese rocket engine to burn a cryogenic fuel. The H in the name stood for the liquid hydrogen fuel of that second stage. Flights to geosynchronous transfer orbit added a Nissan-built UM-69A solid motor as a third stage, and six or nine American Castor 2 solid boosters were fitted depending on the mass of the payload. Announced in 1986 for Japanese payloads only, at two launches a year and in a four-month window chosen to keep falling boosters away from fishing fleets, it replaced the N-II and was succeeded by the H-II, which kept its upper stages and gained a Japanese first stage.