Performance and flow characteristics of a conical microthruster operated in cold thruster mode are presented. Nitrogen, Argon and Carbon dioxide were used as the medium. The performance parameters (specific impulse, impulse efficiency, thrust coefficient and characteristic velocity) are measured. The chamber pressure was varied from 2.8 bar to 12 bar. It is found that the high viscous loss severely degrades the performance of the thruster at a pressure below 5 bar. However, the mass flow remains unaffected even at a low pressure. The computed Mach number shows that at low pressures flow separates earlier. The schlieren photographs show the flow development inside the thruster at different pressures. Interestingly, a highly asymmetric flow field exists in the nozzle expansion section. Row perturbation effects cause the flow to separate from the upper wall and to remain attached with lower wall.

Dynamic instability induced by the initiation and development of mechanical faults in a rotary element is known to have a large negative impact on the reliability and operation safety of an entire system. This type of nonlinear system response is generally perturbed by shock impulses of extremely short time scale and amplitude. Thus difficulty presents itself in identifying and isolating features indicative of the presence and progression of faults possibly leading to mechanical deterioration. The perturbed and deteriorated states of a bearing-shaft system subjected to the actions of various types of commonly seen mechanical faults are investigated using the Numerical Hilbert Transform. The presented approach characterizes and realizes temporal events of both short and long time scales as instantaneous frequencies in the joint time-frequency domain. Examples are given to demonstrate the feasibility of applying the approach to the characterization of various deteriorating bearing states and the identification of parameters associated with several failure modes.