I'm searching for any design file or deep-info on the MT-135 rocket, the fuel used, engines, engines info, any thing really. I have deep-searched on tons of sites but I just find few missions that used this rocket; I would like all the possible info. Thanks and regards.
According to the JAXA page about the rocket, it's a solid-fuel motor:
The propellant, a pre-formed grain, polyurethane composite with a low burning rate...
By polyurethane composite I assume they mean HTBP plus ammonium perchlorate and aluminum powder, since that's what JAXA generally uses for solid rockets. Since it's a solid rocket stage, the motor itself doesn't have its own name or an identity outside of the MT-135.
The page gives quite a bit of information about the construction as well:
The [combustion] chamber is built up by welding tubes made of chromium-molybden steel, and the outer edge of the nozzle is welded to it. The throat insert material is graphite, and the exit cone is made of ablative silica-phenolic FRP [fiber-reinforced phenolic, i.e. fiberglass]
The motor casing in the later MT-135P is recoverable by parachute, but the nozzle materials are ablative, so would be replaced after each flight.