The J-I launch vehicle is a three-stage solid fuel rocket with the ability to launch an approximately one-ton satellite into low-earth orbit. It was developed in response to expected demands for the launch of smaller satellites. The J-I is the first rocket in Japan to be developed by combining existing rockets. It combines the solid rocket booster (SRB) of the H-II developed by NASDA with the upper stage of the M-3SII rocket developed by the Institute of Space and Astronautical Science (ISAS) of the Ministry of Education. This has enabled rapid development at low cost. Also compared to a large-scale liquid rocket, a solid rocket makes it possible to greatly reduce launch site operations.
The development of the second J-I launch vehicle has been suspended, according to a reexamination in the Space Development plan of space Activities Commission.