Stability of the dynamics of spinning spacecraft equipped with a large flexible membrane is discussed. The spin stability of an object having a flexible structure is deteriorated from that of a rigid object with the same shape in general, which makes a significant impact on the design of such spacecraft systems. This paper provides a fully analytical solution for the stability criteria of axisymmetric spinner spacecraft equipped with a large flexible membrane. Distinct from past studies, this paper does not impose restrictions on axial offset of the membrane attachment, and provides a stability condition using energy-angular momentum analysis when the membrane is subject only to an outer-plane first-order mode deformation. These criteria can be applied to the design of such missions as spinner solar sail spacecraft, large solar power satellite and other general spacecraft with large axisymmetric structures.
We have investigated a new method of risk/reliability assessment for development and operation of space system. It is difficult to evaluate risk of spacecraft, because of long time operation, maintenance free and difficulty of test under the ground condition. Conventional methods are FMECA, FTA, ETA and miscellaneous. These are not enough to assess chronological anomaly and there is a problem to share information during R&D. A new method of risk and reliability assessment, T-TRAP (Time-tagged Risk/Reliability Assessment Program) is proposed as a management tool for the development and operation of space system. T-TRAP consisting of time-resolved Fault Tree and Criticality Analyses, upon occurrence of anomaly in the system, facilitates the responsible personnel to quickly identify the failure cause and decide corrective actions. This paper describes T-TRAP method and its availability.
A half-toroidal traction drive CVT has a feature of small spin at traction pitch in whole speed ratio range of 1:4, which suits to transmit high rotational speed with minimum temperature increase of traction surface. Research activity on traction drive CVT has commenced in 1996 for applying it to an aircraft 24,000rpm constant-speed generator instead of a hydro-static transmission. This paper shows fundamental design of 90kW traction drive integrated drive generator, ``T-IDG", and stability analysis on a sensor-less electro-hydraulic speed control servo-mechanism by bond graphs. The performance test of T-IDG mounted on a test bench and an actual jet engine proved that the control system using sensor-less servomechanism can keep the generator speed within MIL-STD-704E allowable limit against steep changes of speed and load.
A spot, generated by an artificial disturbance introduced into a laminar boundary layer, had a highly reproducibility in its velocity perturbations during the initial stage of its downstream development. Thus, we called it a ``laminar spot'' and investigated its downstream development in detail. The purpose of this study was to investigate the generation and the development of an irregularity observed in the velocity waves during the laminar-turbulent transition of the spot. The results obtained show that those irregularities appeared locally in the low-speed region away from the wall and spread wide close to the wall. In the beginning, lateral distortion of velocity profile due to the vortex-interaction caused the irregularity of the velocity-wave amplitude in the boundary between the low- and high-speed regions in the spot. In addition, the crossover of legs of the longitudinal vortices occurred incidentally in the spot and generated a local ejection of low-momentum fluid. Afterwards, some crossovers of legs were produced in a chain reaction. Consequently, the reproducibility in the velocity waves disappeared almost in the downstream and turbulent regions increased rapidly everywhere in the spot.