We present a characterization of the performance of a recently developed gas-fed pulsed plasma thruster (GF-PPT) at low discharge energies (≤5 J). The impulsive thrust measurements were made using EPPDyL's high-accuracy interferometric microthrust stand. The thruster is best suited for small satellite applications and is operated in an unsteady pulsed mode (3 µs/pulse). It is the result of a series of design iterations aimed at achieving the highest thrust efficiencies for unsteady electromagnetic acceleration at low discharge energies. The use of advanced nonlinear magnetic switching technology, which insured a total system inductance of 3-4 nH, combined with an electrode geometry and radial gas injection that favor low profile losses, yielded a total efficiency of 50% at 5 J with argon (at an impulse bit of 32 µNs and a mass bit of .2 µg/shot). This is the highest measured efficiency ever reported for a PPT at this low energy level. Moreover, the low mass utilization efficiency problem that plagued previous gas-fed pulsed

An optical interferometric proximeter system (IPS) for measuring thrust and impulse bit of pulsed electric thrusters was developed. Unlike existing thrust stands, the IPS-based thrust stand offers the advantage of a single system that can yield electromagnetic interference-free, high accuracy (<2% error) thrust measurements within a very wide range of impulses (100 μN s to above 10 N s) covering the impulse range of all known pulsed plasma thrusters. In addition to pulsed thrusters, the IPS is theoretically shown to be capable of measuring steady-state thrust values as low as 20 μN for microthrusters such as the field emission electric propulsion thruster. The IPS-based thrust stand relies on measuring the dynamic response of a swinging arm using a two-sensor laser interferometer with 10 nm position accuracy. The wide application of the thrust stand is demonstrated with thrust measurements of an ablative pulsed plasma thruster and a quasi-steady magnetoplasmadynamic thruster.

The final design of an optical Interferometric Proximeter System (IPS) for measuring the thrust of pulsed thrusters, in particular pulsed plasma thrusters, has been completed. This paper reports the recent improvements of the IPS and reviews the basic principles. Unlike existing thrust stands, the IPS-based thrust stand offers the advantage of a single system that can yield EMI-free, high accuracy (< 2% error) thrust measurements within a very wide range of impulses (100 µN-s to above 10 N-s) covering the impulse range of all known pulsed plasma thrusters. At very low thrust levels the IPS becomes ideally suited for measuring the performance of steady state thrusters such as the FEEP thruster. The IPS is capable of measuring steady state thrust values as low as 10 µN-s. The IPS-based thrust stand relies on measuring the dynamic response of a swinging arm using a two-sensor laser interferometer with 10 nm position accuracy. The wide application of the thrust stand is demonstrated with thrust measurements of an ablative pulsed plasma thruster (APPT) and a gas-fed Magnetoplasmadynamic (MPD) thruster. The LES 8/9 APPT average mass bit and efficiency are presented. Lastly, a power spectrum method is presented for maximizing the signal to noise ratio of the experiment.

Pre-launch characterization and preparation of a Lincoln Experimental Satellite (LES 8/9) ablative pulsed plasma thruster (APPT) module for the COMPASS P 3 OINT Mission are described. COMPASS P 3 OINT is a joint project between the Electric Propulsion and Plasma Dynamics Lab (EPPDyL) of Princeton University and the Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Science (IZMIRAN) to carry inorbit investigations with an ablative pulsed plasma thruster onboard COMPASS, an IZMIRAN scientific microsatellite to be launched in October, 1996. The unmodified LES 8/9 APPT module produces impulse bits of 285 µN-s at an I sp of 836 s using 25 W of power on average. The APPT module will be used to conduct in-orbit investigations of pulsed plasma propulsion as well as to provide attitude control of the satellite and a source of plasma for active space experiments. Details of the power, command, and telemetry signals required to operate the device on the COMPASS satellite are presented. Thermal control and various operational modes are also outlined.