The high-speed bearings and rotating-shaft seals of turbopumps which supply extremely low temperature propellants such as liquid oxygen (LO2) and liquid hydrogen (LH2) to liquid rocket engines are very important parts. However, the operating conditions of turbopump bearings and shaft seals are characterized by poor lubrication because of the low viscosity due to oxidation (LO2) or reduction (LH2). Therefore, turbopump bearings and shaft seals must be highly durable and reliable under extreme operating conditions in LO2 and LH2 environment. As a means of reducing launch costs, reusable rocket engines are required for future space transportation systems, and the durability of bearings and shaft seals in reusable turbopumps must be much greater than that of currently expendable turbopump bearings and shaft seals. For example, the required life of the reusable turbopump bearings and shaft seals of the space shuttle main engine (SSME) is 7.5 hours, which is 15 times longer than that required for the expendable LE-7 engine of the Japanese H-II rocket. However, a serious wear problem has been reported for the turbopump bearings of the SSME and hybrid ceramic bearings are now used in an attempt to reduce serious bearing wear. In order to develop turbopump bearings and shaft seals, many tribological problems for extremely low tomperatures and high rotating speeds must be solved. The cryogenic tribological problems experienced in the development of the turbopump bearings and shaft seals of the LE-5 engine for the H-I rocket and the LE-7 engine for the H-II rocket are introduced in this report. Additionally, the performance of a self-lubricating hybrid ceramic bearing developed to increase bearing life is described.
The degradation of the inter-laminar shear strength (ILSS) of GFRPs was evaluated after electron irradiation at 77K and reactor irradiation at 20K. The GFRPs used in this study were prepared by varying matrix resins. Optical microscopic observation of the fracture surface was carried out to reveal the degradation behavior of the ILSS. The exposed fiber area of the fracture surface was found to depend on the absorbed dose. This suggests that a change in ILSS is induced by the interface failure between fiber and matrix as a result of the change in matrix resin.
Cable-in-conduit conductors (CICCs), composed of multi-strand superconducting cables cooled with supercritical helium, are essential to superconducting magnets that require large current capacities, low AC losses and high rigidity for fusion machines. A conductor cabled by several hundreds of superconducting strands with superficial chrome plating, oxide or CuNi result in the problem of unbalanced current distribution among the strands. This is caused by small differences in the self-inductance of each strand as well as an electrical resistance difference several times larger at the portion of electrical contacts between each strand and the current leads. This unbalanced current decreases the minimum quench energy (MQE) under the case of uniform current distribution. The MQE of CIC multi-strand cables under unbalanced current distribution is greatly affected by the electrical resistance among the strands. This means that the stability is influenced by the current-sharing process among strands. A higher margin of stability is induced by increasing current sharing and more rapid current transfer to the neighboring strands rather than thermal diffusion to helium. The most suitable parameter to govern this process is the impedance between strands. A simplified electrical circuit model simulating the current-sharing process among strands was proposed to estimate stability. The circuit parameters, that is the impedance, governing the sharing process were measured easily using short samples of CIC cables at 4.2K. The experimental results of stability tests show that the CIC has an extensive stability margin according to lower impedance between strands. We also confirm that the proposed method is applicable to estimate the stability of CIC.