Pulsed thrust measurements using laser interferometry

An optical interferometric proximeter system (IFS) for measuring thrust and impulse bit of pulsed electric thrusters was developed; Unlike existing thrust stands, the IFS-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 mu N s to above 10 N s) covering the impulse range of all known pulsed plasma thrusters. In addition to pulsed thrusters, the IFS is theoretically shown to be capable of measuring steady-state thrust values as Tow as 20 mu N for microthrusters such as the field emission electric propulsion thruster. The IFS-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. (C) 1997 American Institute of Physics.