Reusable sounding rocket engine and its tribological subjects

A fully reusable sounding rocket has been proposed by JAXA/ISAS to provide frequent opportunities for high altitude atmospheric observation missions at low cost and with short turnaround time, and also to improve technology readiness levels for reusable space transportation systems. This rocket will take off vertically, reach an altitude of more than 100 km, land on the launch site vertically, and be launched again within 24 hours. The main propulsion system will consist of clustered LOX/LH2 engines with full-time abort capability in case of the failure of one engine. In order to realize the reusable sounding rocket, the main propulsion system should have advanced features of high reliability, reusability, maintainability, and survivability. To fulfill those requirements, the following points were considered and reflected in the engine system design, i.e., optimization of design margins among components for high reliability and reusability, deep throttling capability for vertical landing, and health monitoring capability for abort operation, easy inspection and maintenance for short turnaround time. Those functions and performance have been verified and demonstrated through ground tests at Kakuda Space Center/JAXA in 2014. This paper shows the design considerations, the design of the engine system and its major components, and the tribological properties of bearings and seals of turbopumps.