S-Series is a fleet of sounding rockets funded by the Japan Aerospace Exploration Agency (JAXA) that have been in service since the late 1960s. Manufactured by IHI Aerospace and operated by the Institute of Space and Astronautical Science (ISAS). The nomenclature of the S-Series rockets is the number of "S"s indicates the number of stages, and the following number details the diameter of the craft in millimeters.
On January 14, 2017, the SS-520-4 rocket (modified sounding rocket) attempted to become the lightest and smallest launch vehicle to send a payload to orbit, however, the rocket failed to reach orbit. A second attempt was made on February 3, 2018. This time, the rocket reached orbit and successfully deployed TRICOM-1R (Tasuki), a 3U CubeSat. Its 2019 launch made it the smallest orbital rocket both in mass and height.