Pulsed thrust measurements using laser interferometry

36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit

Levine

et al. 2000

The Z-pinch configuration in gas-fed devices was adapted for an ablative Pulsed Plasma Thruster (PPT). The motivation stems from the promise of the Z-pinch configuration for increasing the thrustto-power ratio and mass utilization efficiency. A series of ablative Z-pinch PPTs were constructed and their performance measured using a swinging gate thrust stand and mass ablation measurements. Several iterations of the design lead to the selection of a thruster with an augmented "spike" inner electrode for more exhaustive testing. Peak performance parameters for this configuration were found to be: I ×Ô s, Ø = 7.5 %, and T/P = 28 N/W. In order to determine whether the plamsa was pinching, photographs of the discharge were acquired using a modified thruster having transparent Plexiglas propellant and mesh sidewalls. A current sheet structure leading to a plasma pinch was observed.

Section: A3 Liquid Nitrogen Cold Trapmentioning

confidence: 99%

Ablative Z-pinch pulsed plasma thruster

Markusic

36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit

Levine

et al. 2000

“…The problem is compounded when a pulsed thruster is tested, as it subjects the thrust measurement device to an unsteady force. Work by Cubbin et al, 2 Haag, 3 and Markusic et al 4 present pulsed thrust measurement results obtained using torsional thrust stands where the pulsed thruster applied an impulse bit (impulse per pulse) to a swinging-gate thrust stand arm. In all three works the thrust balance response was calibrated by imparting an impulsive force (on the time scale of thrust stand motion) to the movable thrust stand arm using a swinging mass.…”

Section: Introductionmentioning

confidence: 99%

“…We also demonstrate in this paper that the measurement of the average thrust stand deflection during repetitively-pulsed calibration or operation is almost universally appropriate for the measurement of the average thrust and impulse bit, which for repetition-rate pulsing will obviate the need in the future to measure and anaylze the time-resolved motion of the thrust stand as is presently used when performing single pulse thrust stand measurements. 2,4 The outline for the rest of this paper is as follows. In Section II we present an analytical model for thrust stand response to an arbitrary number of pulses.…”

Section: Introductionmentioning

confidence: 99%

“…[3] by calculating the momentum transfer during the impact from the measured change in velocity of the swinging mass and in Refs. [2,4] by directly measuring the imparted force using a piezoelectric force transducer. Knowing the thrust balance response to measured impulsive forces permitted the determination of a pulsed thruster's unknown impulse bit by measuring the response of the thrust balance.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Non-contact thrust stand calibration method for repetitively pulsed electric thrusters

Wong

Toftul

Review of Scientific Instruments

et al. 2012

A thrust stand calibration technique for use in testing repetitively-pulsed electric thrusters for in-space propulsion has been developed and tested using a modified hanging pendulum thrust stand. In the implementation of this technique, current pulses are applied to a solenoidal coil to produce a pulsed magnetic field that acts against the magnetic field produced by a permanent magnet mounted to the thrust stand pendulum arm. The force on the magnet is applied in this non-contact manner, with the entire pulsed force transferred to the pendulum arm through a piezoelectric force transducer to provide a time-accurate force measurement. Modeling of the pendulum arm dynamics reveals that after an initial transient in thrust stand motion the quasisteady average deflection of the thrust stand arm away from the unforced or 'zero' position can be related to the average applied force through a simple linear Hooke's law relationship. Modeling demonstrates that this technique is universally applicable except when the pulsing period is increased to the point where it approaches the period of natural thrust stand motion. Calibration data were obtained using a modified hanging pendulum thrust stand previously used for steady-state thrust measurements. Data were obtained for varying impulse bit at constant pulse frequency and for varying pulse frequency. The two data sets exhibit excellent quantitative agreement with each other as the constant relating average deflection and average thrust match within the errors on the linear regression curve fit of the data. Quantitatively, the error on the calibration coefficient is roughly 1% of the coefficient value.

“…Consequently, torsional pendulum thrust stands possess the highest sensitivity of any of the thrust stand configurations. [15][16][17][18][19][20][21] Torsional thrust stands have been recently used in the evaluation of microthruster performance, 5,[22][23][24] and they have been effective in measuring the performance of pulsed thrusters. In general, present thrust stands for EP are designed for use in vacuum facilities where the thrust axis is aligned parallel with the horizontal.…”

Section: Introductionmentioning

confidence: 99%

Thrust stand for vertically oriented electric propulsion performance evaluation

Moeller

Review of Scientific Instruments

2010

A variation of a hanging pendulum thrust stand capable of measuring the performance of an electric thruster operating in the vertical orientation is presented. The vertical orientation of the thruster dictates that the thruster must be horizontally offset from the pendulum pivot arm, necessitating the use of a counterweight system to provide a neutrally-stable system. Motion of the pendulum arm is transferred through a balance mechanism to a secondary arm on which deflection is measured. A non-contact light-based transducer is used to measure displacement of the secondary beam. The members experience very little friction, rotating on twisting torsional pivots with oscillatory motion attenuated by a passive, eddy current damper. Displacement is calibrated using an in situ thrust calibration system. Thermal management and self-leveling systems are incorporated to mitigate thermal and mechanical drifts. Gravitational restoring force and torsional spring constants associated with flexure pivots provide restoring moments. An analysis of the design indicates that the thrust measurement range spans roughly four decades, with the stand capable of measuring thrust up to 12 N for a 200 kg thruster and up to approximately 800 mN for a 10 kg thruster. Data obtained from calibration tests performed using a 26.8 lbm simulated thruster indicated a resolution of 1 mN on 100 mN-level thrusts, while those tests conducted on 200 lbm thruster yielded a resolution of roughly 2.5 mN at thrust levels of 0.5 N and greater.