Thrust Stand:

With the original thrust stand, thruster performance measurements are made with an inverted pendulum type thrust stand based on the NASA LeRC/GRC design, the industry standard. The thruster is mounted to an aluminum plate that is connected to the core of a Lucas Schaevitz model 100-HR Linear Variable Differential Transformer (LVDT). The core resides within a LVDT coil that is mounted to the base of the thrust stand. Thus, the thrust stand measures the displacement of the aluminum plate due to engine thrust. The output from the LVDT is routed to a Lucas Schaevitz DTR-451 Digital Transducer Readout (DTR) and to the data acquisition system. Thruster/thrust-stand leveling is performed manually before chamber pump-down so that the LVDT core is in its null position within the coil. A remotely controlled stepper motor driven pulley system is employed to provide in-situ thrust stand calibration by loading and off-loading small weights to simulate thrust. A linear curve-fit of LVDT displacement vs. thrust is then obtained and used for performance measurements. Soon after the thruster is turned off, a post-test calibration is performed. The springs of the stand are made with extra stiffness to minimize thruster deflection, thus allowing plume measurements to be made concurrently with performance measurements.

Thrust data, based on the predetermined curve fit, are displayed and simultaneously stored on the hard disk by the DAQ system. The DAQ system also reads mass flow rate, current, and voltage, enabling it to calculate thrust efficiency and specific impulse in real-time.