The M-V rocket, which was retired in 2006, was the highest-performance solid rocket system with all solid motor stages in the world. It was even capable of launching planetary exploration satellites. Know-how accumulated over 50 years of research in indigeneous Japanese solid rockets was embedded in every subsystem design in the rocket. It is no exaggeration to say that the entire rocket was like a brilliant crystal formed by a combination of all marvelous technologies.
However, the M-V rocket had its weak points: high cost because of rocket optimization focused on performance only and outdated concepts for launch operation and ground systems in rocket assembly and checkup. The latter factor was a result of the limited development fund spent mostly on the vehicle development. Preparation for launch at the Uchinoura Space Center required considerable manpower and time. Consequently, it was physically difficult to launch the M-V rocket at an interval of less than six months. Due to these weaknesses, the M-V rocket did not demonstrate that solid rockets are much easier to launch than liquid-type rockets.
On the other hand, new requirements are emerging from the science side. In the past, scientific satellites launched by the M-V rockets have successfully obtained many world-leading observational results. Because these are large-scale satellites, high costs and long development lead-time were unavoidable. Launch opportunities are also limited. The new policy of the science side is, “We want to launch satellites more frequently even if downsizing of satellites is requested.” Of course, large missions will continue to be necessary in the future as before. However, the science side intends to conduct more flexible small satellite missions at lower cost.
With this as background, the goal of the next solid rocket is to realize not only high performance but also low cost and good operability, i.e., a rocket system in the new era (Fig. 1).