A COMPACT THRUST STAND FOR PULSED PLASMA THRUSTERS

A compact thrust stand has been developed for performance measurements on pulsed plasma thrusters in the l-100 joule energy range, and used to determine the single-pulse impulse bit and efftciency of a coaxial PPT. The thrust stand, which can support a thruster mass of up to 50 kg on a 20x39 cm platform, is based on a long-period pendulum design which uses the Watt straight-line mechanism, and achieves periods of over 20 seconds by adjusting the center of gravity. A period of 10 seconds is typical for thrust measurements. Platform motion is de&c&d by a linear variable differential transformer, and both DC and impact calibration are employed to achieve an accuracy of 25% at 150 pN. Single-pulse measurements show the impulse bit of a coaxial Teflon PPT to be linear with energy at 60 pN-s/J, at an efficiency of 12 - 17% at 600 seconds specific impulse.